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We discuss the nonlinear process of optical parametric amplification inside a chiral crystal. We show that circular birefringence, induced by chirality, leads to two different nonlinear processes with different phase-matching conditions that are associated with the opposite states of circular polarizations. A single nonlinear process occurs only when the states of polarization of the incident pump and signal beams are both circular and orthogonal. When these beams are linearly polarized initially, their state of polarization evolves in an elliptical fashion because of the two competing nonlinear processes taking place in parallel. We also discuss the properties of singly and doubly resonant optical parametric oscillators made by placing a chiral nonlinear crystal inside an optical cavity. [ABSTRACT FROM AUTHOR]

We use optical–optical double-resonance spectroscopy with a continuous wave (CW) pump and a cavity-enhanced frequency comb probe to measure the energy levels of methane in the upper part of the triacontad polyad (P6) with higher rotational quantum numbers than previously assigned. A high-power CW optical parametric oscillator, tunable around 3000 cm−1, is consecutively locked to the P(7, A2), Q(7, A2), R(7, A2), and Q(6, F2) transitions in the ν3 band, and a comb covering the 5800–6100 cm−1 range probes sub-Doppler ladder-type transitions from the pumped levels with J′ = 6 to 8, respectively. We report 118 probe transitions in the 3ν3 ← ν3 spectral range with uncertainties down to 300 kHz (1 × 10−5 cm−1), reaching 84 unique final states in the 9070–9370 cm−1 range with rotational quantum numbers J between 5 and 9. We assign these states using combination differences and by comparison with theoretical predictions from a new ab initio-based effective Hamiltonian and dipole moment operator. This is the first line-by-line experimental verification of theoretical predictions for these hot-band transitions, and we find a better agreement of transition wavenumbers with the new calculations compared to the TheoReTS/HITEMP and ExoMol databases. We also compare the relative intensities and find an overall good agreement with all three sets of predictions. Finally, we report the wavenumbers of 27 transitions in the 2ν3 spectral range, observed as V-type transitions from the ground state, and compare them to the new Hamiltonian, HITRAN2020, ExoMol, and the WKMLC line lists. [ABSTRACT FROM AUTHOR]

Spectra of mixed H/D water dimers are studied in the mid-infrared region of the O–D stretch fundamental (2630–2800 cm−1) using a pulsed supersonic slit jet and a tunable optical parametric oscillator infrared source. Over 30 bands, belonging to nine of the ten possible isotopologues (only H2O–HOD is missed), are observed and analyzed. The implications for excited state tunneling splittings, lifetime effects, and vibrational shifts are discussed. These are the first significant new experimental results on (gas phase) mixed water dimers in over 25 years, and they are valuable for testing water dimer theoretical calculations, a field which continues to be of lively current interest. [ABSTRACT FROM AUTHOR]

Zinc germanium diphosphide (ZnGeP2) is a ternary semiconductor best known for its nonlinear optical properties. A primary application is optical parametric oscillators operating in the mid-infrared region. Controlled donor doping provides a method to minimize the acceptor-related absorption bands that limit the output power of these devices. In the present study, a ZnGeP2 crystal is doped with selenium during growth. Selenium substitutes for phosphorus and serves as a deep donor. Significant concentrations of native defects (zinc vacancies, germanium-on-zinc antisites, and phosphorous vacancies) are also present in the crystal. Electron paramagnetic resonance (EPR) is used to establish the atomic-level model for the neutral charge state of the selenium donor. The S = 1/2 signal from the neutral donors is produced at 6 K by illuminating with 633 nm light (electrons excited from doubly ionized Zn vacancies convert Se P + donors to Se P 0 donors). A g matrix, with principal values of 2.088, 2.203, and 1.904, is extracted from the angular dependence of the EPR spectrum. The principal-axis direction associated with the 1.904 principal value is close to a Se–Ge bond. This indicates an asymmetric distribution of unpaired spin density around the selenium ion and thus predicts the deep donor behavior. [ABSTRACT FROM AUTHOR]

Coherent Ising Machine (CIM) is a network of optical parametric oscillators that solve combinatorial optimization problems by finding the ground state of an Ising Hamiltonian. In CIMs, a problem arises when attempting to realize the Zeeman term because of the mismatch in size between interaction and Zeeman terms due to the variable amplitude of the optical parametric oscillator pulses corresponding to spins. There have been three approaches proposed so far to address this problem for CIM, including the absolute mean amplitude method, the auxiliary spin method, and the chaotic amplitude control (CAC) method. This paper focuses on the efficient implementation of Zeeman terms within the mean-field CIM model, which is a physics-inspired heuristic solver without quantum noise. With the mean-field model, computation is easier than with more physically accurate models, which makes it suitable for implementation in field programmable gate arrays and large-scale simulations. First, we examined the performance of the mean-field CIM model for realizing the Zeeman term with the CAC method, as well as their performance when compared to a more physically accurate model. Next, we compared the CAC method to other Zeeman term realization techniques on the mean-field model and a more physically accurate model. In both models, the CAC method outperformed the other methods while retaining similar performance. [ABSTRACT FROM AUTHOR]

Optical computing often employs tailor-made hardware to implement specific algorithms, trading generality for improved performance in key aspects like speed and power efficiency. An important computing approach that is still missing its corresponding optical hardware is probabilistic computing, used e.g. for solving difficult combinatorial optimization problems. In this study, we propose an experimentally viable photonic approach to solve arbitrary probabilistic computing problems. Our method relies on the insight that coherent Ising machines composed of coupled and biased optical parametric oscillators can emulate stochastic logic. We demonstrate the feasibility of our approach by using numerical simulations equivalent to the full density matrix formulation of coupled optical parametric oscillators. Optical computing often employs tailor-made hardware to implement specific algorithms, trading generality for improved performance in key aspects like speed and power efficiency. We propose an experimentally viable photonic approach to solve arbitrary probabilistic computing problems, used e.g. for solving difficult combinatorial optimization problems. [ABSTRACT FROM AUTHOR]

Herein, we present a picosecond-pulsed optical vortex parametric oscillator capable of generating high-power, narrow-linewidth near- and mid-infrared optical vortex outputs. The optical parametric oscillator (OPO), consisting of a KTiOAsO4 (KTA) crystal and a Z-shaped standing wave cavity formed by five mirrors, transferred the orbital angular momentum (OAM) of the pump field to the signal and idler fields. The transmission mechanism of the OAM within the signal singly resonantsingly-resonant KTA-OPO was investigated, and the OAM was controlled and selectively transferred among the pump, signal, and idler fields by adjusting the focus position of the pump beam on the KTA crystal. With an incident pump power of 17 W, the maximum average output power was 2.14 W at 1535 nm (signal vortex field) and 0.95 W at 3468 nm (idler vortex field), respectively, corresponding to optical conversion efficiencies of 20.8% and 9.2%. The spectral linewidths of the signal and idler vortex fields were 0.502 nm and 1.216 nm, respectively. To the best of our knowledge, this is the first instance of a picosecond-pulsed optical vortex parametric oscillator with a KTA crystal. [ABSTRACT FROM AUTHOR]

We report efficient generation of ultrashort laser pulses in the deep ultraviolet (DUV) from a quasi-phase-matched (QPM) optical parametric oscillator (OPO) based on a periodically poled KTP (PPKTP) crystal. Up-conversion through frequency-doubling of the signal pulses (2ωS) and sum-frequency generation between the pump and signal pulses (ωP + ωS) produces femtosecond pulses in the green and in the blue, respectively. A third-order QPM is responsible for the green-pulse generation and a fifth-order QPM for the blue. The cavity mirrors have two high-reflection bands, which support the oscillation of the OPO signal (ωS) in the near infrared and the sum-frequency generation of ωP + ωS in the blue, respectively. The interaction between the blue and green pulses enables further cascading by a sum-frequency generation process, producing the DUV pulses. Cavity-length detuning facilitates the large tuning range of the DUV generation. [ABSTRACT FROM AUTHOR]

In this paper, a high energy 3.5 μm mid-infrared (MIR) burst-mode KTA optical parametric oscillator (OPO) was demonstrated. Utilizing a quasi-continuous wave (QCW) laser diode (LD) side-pump module and electro-optic (EO) Q-switching technique, a high beam quality 1064 nm burst-mode laser was achieved as the fundamental source, generating 30 mJ high-energy pulses at burst repetition rates of 100 Hz and 200 Hz with sub-burst repetition rates of 20 kHz, 40 kHz, and 50 kHz. The KTA-OPO produced a 3.5 μm MIR burst-mode laser output with 4 to 11 sub-pulses per pulse envelope. The output energies were 2.9 mJ, 2.81 mJ, and 2.79 mJ at 100 Hz, as well as 2.8 mJ, 2.75 mJ, and 2.72 mJ at 200 Hz, with corresponding conversion efficiencies of 9.6%, 9.3%, and 9.3% at 100 Hz, as well as 9.3%, 9.2%, and 9.1% at 200 Hz, respectively. Our results pave a new way for generating burst-mode MIR lasers. [ABSTRACT FROM AUTHOR]

Soliton molecules (SMs) play a crucial role in nonlinear optical systems, enriching our understanding of nonlinear science through the study of their interaction dynamics. While passively mode-locked fiber lasers offer an efficient platform for generating diverse types of SMs, the complex internal dynamics of the laser often pose challenges in achieving predetermined temporal separations between SMs. Here, we implement a delayed optical feedback technique within a femtosecond optical parametric oscillator, enabling the generation of SMs with precise and controllable temporal separations. A theoretical model, which models the intracavity iterations of the signal with a simplified Ikeda map, is proposed to study the impact of parametric gain, intracavity feedback delay, and cavity length on the internal separations of the SMs. Our experimental results confirm that adjusting the cavity length allows for producing desired temporal separations within SMs. To reveal the evolution dynamics of the SMs, we further develop a rigorous numerical model using the carrier-resolved Forward Maxwell Equation, which is capable of modeling ultra-broadband complex dynamics based on a single equation without relying on the slowly-varying envelope approximation. The numerical model unveils the rich formation dynamics of the SMs at various separations, which confirms the critical role of the gain window provided by the pump. This work opens up new opportunities for the on-demand generation of SMs and provides valuable insights into the complex dynamics in femtosecond optical parametric oscillator systems with optical delayed feedback. [ABSTRACT FROM AUTHOR]

Within the domain of optical frequency comb systems operating in the mid-infrared region, extensive exploration has been undertaken regarding critical parameters, such as stabilization, coherence, or spectral tunability. Despite this, certain essential parameters remain inadequately addressed, particularly concerning light source stability at high average powers. This study explores stability limitations of an optical parametric oscillator system when scaling to several watts of average power of the idler. Notably, the highest average power reported in the 3–5 μm region, reaching 10.3 W for the idler output at 3.1 μm, is achieved. Additionally, we analyze the phase noise and beam quality of both idler and signal beams and identify the onset of higher order modes as limiting for stability at high-power operation. Finally, we estimate the free-running optical linewidth of our idler beam to be ∼300 kHz, undermining the high passive temporal stability of our source. These findings represent a significant advancement toward the realization of highly stable high-power optical frequency combs in the mid-infrared region, thereby facilitating applications previously constrained by light source average powers and quality limitations. [ABSTRACT FROM AUTHOR]

We report on a nanosecond-pulsed CdSiP2 (CSP) optical parametric oscillator (OPO) pumped by a Q-switched 2.06 µm Ho:LiLuF4 (Ho:LLF) laser in a compact linear cavity with a 10 mm long crystal. Utilizing a non-collinear type-I phase-matching configuration, the OPO achieved an average output power exceeding 3 W in the mid-IR region with good beam quality. The idler and signal waves can be tuned in a wide range of 3.5–4.7 µm by pump tilt and crystal rotation. [ABSTRACT FROM AUTHOR]

Note: Photoelectron imaging of MnO3- to probe its nuclear and electronic structure In this note, we revisit the MnO SB 3 sb SP - sp photoelectron spectrum using photoelectron imaging and reassess the assignment, showing that in fact, MnO SB 3 sb is planar in its ground electronic state. Using anion photoelectron spectroscopy, a previous study by Gutsev I et al. i [1] found the ground state of MnO SB 3 sb to have a trigonal pyramidal structure. A 126(22), 3495-3501 (2022). 10.1021/acs.jpca.2c02008 9 J. B. Kim, M. L. Weichman, and D. M. Neumark, "Structural isomers of Ti2O4 and Zr2O4 anions identified by slow photoelectron velocity-map imaging spectroscopy", J. Am. Chem. Soc. 136(19), 7159-7168 (2014). 10.1021/ja502713v 10 V. D. Moravec and C. C. Jarrold, "Study of the low-lying states of NiO- and NiO using anion photoelectron spectroscopy", J. Chem. Phys. [Extracted from the article]

Lithium niobate (LN) crystal with anti‐reflective subwavelength structures (ASSs) has great applications in high‐power tunable optical parametric oscillator (OPO) lasers. However, it is still a great challenge to 3D nanofabrication of LN ASSs. Herein, a wet‐etching‐assisted laser polarization domain inversion (WE‐LPDI) technology is proposed to fabricate periodic cone arrays with a period from 200 nm to 4 µm on LN. Based on the optimized structural parameters, large‐area LN ASSs with a period of 1.3 µm and a height of 1.7 µm were fabricated on LN, which exhibits an average transmittance of 3–5 µm increasing from 78% to 85% and a highest transmittance of 88% at 5 µm. It has been demonstrated that the LN ASSs show high stability under high‐temperature and high‐power laser irradiation, which shows potential applications for high‐power mid‐IR lasers. The results indicate that the WE‐LPDI technology provides a novel way for 3D nanofabrication of LN. [ABSTRACT FROM AUTHOR]

A dispersion-managed femtosecond optical parametric oscillator (OPO) with stable power is demonstrated in this article. The OPO, based on LiB3O5 (LBO) crystal, was synchronously pumped by a frequency-doubled, Kerr-lens mode-locked Yb: CGYA laser. The output signal had a wavelength tuning range of 680 ~ 740 nm, a maximum average power of 1.1 W, and a minimum pulse duration of 105 fs. By inserting ultraviolet fused silica (UVFS) windows into the cavity to introduce additional normal dispersion, the dual-signal-wavelength output was suppressed, and the power stability was significantly enhanced. The RMS of the one-hour power fluctuation decreased to one seventh of its original value, from 2.47% to 0.38%. This work is of particular significance for promoting the engineering application of femtosecond OPOs. [ABSTRACT FROM AUTHOR]

Optical solitons have long been of interest both from a fundamental perspective and because of their application potential. Both cubic (Kerr) and quadratic nonlinearities can lead to soliton formation, but quadratic solitons can practically benefit from stronger nonlinearity and achieve substantial wavelength conversion. However, despite their rich physics, quadratic cavity solitons have been used only for broadband frequency comb generation, especially in the mid-infrared. Here, we show that the formation dynamics of mid-infrared quadratic cavity solitons, specifically temporal simultons in optical parametric oscillators, can be effectively leveraged to enhance molecular sensing. We demonstrate significant sensitivity enhancement while circumventing constraints of traditional cavity enhancement mechanisms. We perform experiments sensing CO2 using cavity simultons around 4 μm and achieve an enhancement of 6000. Additionally, we demonstrate large sensitivity at high concentrations of CO2, beyond what can be achieved using an equivalent high-finesse linear cavity by orders of magnitude. Our results highlight a path for utilizing quadratic cavity nonlinear dynamics and solitons for molecular sensing beyond what can be achieved using linear methods. Optical molecular sensors benefit many applications from fundamental science to industry. In this work, the authors leverage the formation dynamics of cavity solitons to achieve molecular sensing in the mid-infrared spectral region. [ABSTRACT FROM AUTHOR]

Trace gas analysis is a key tool for the investigation of man-made environmental pollution as well as for early detection of respiratory diseases. To detect tiny concentrations, sensitive methods such as cavity ring down spectroscopy or plasmonic sensors have been used. Here, we demonstrate the combination of the photoacoustic effect in a classical cell with a novel, rapidly tunable, narrowband fiber-feedback optical parametric oscillator. The high sensitivity of photoacoustic cells and the extremely narrow linewidth as well as the wide and rapid tunability of the fiber-feedback optical parametric oscillator enable a high resolution of the rotational and vibrational bands of molecules in the near-infrared region. Photoacoustic spectra of methane, carbon dioxide, and water at ambient pressure are obtained in a broad spectral range and compared to high-resolution transmission molecular absorption database. In particular, scanning the entire carbon dioxide overtone around 4965 cm−1 at 2000 ppm takes 185 s with a signal-to-noise ratio of 31. This approach enables a wide tunability in the entire near- and mid-infrared spectral region suitable for many environmental and medical applications. [ABSTRACT FROM AUTHOR]

The ion temperature is an important parameter for ionospheric detection, yet there is limited research on ion temperatures at altitude range from 80 to 300 km. Currently, a single‐frequency Ca+ ion optical parametric oscillator (OPO) Lidar system can be used to obtain the Ca+ ion density in this region at Yanqing Station, Beijing (40.4°N, 116.0°E). In this study, the ion temperature can be obtained by extending our original lidar to include three‐frequency Ca+ Doppler detection. This development represents a pioneering step on measuring ion temperatures by lidar in the ionospheric E‐F region. Preliminary results in the E region show that lidar temperatures at 90–105 km under the condition of smooth changes in Ca+ ion morphology align reasonably with satellite‐based observations and model‐derived temperatures. Additionally, the exploratory ion temperatures of the F layer peak heights at 200–300 km were obtained. Furthermore, parameter optimization and temperature error analysis in the E‐F region are explored, providing valuable insights for the development of Ca+ Doppler lidar systems. The advent of Ca+ Doppler lidar has greatly expanded the lidar detection altitude range of temperature and the possibilities for in‐depth research on ion temperature and velocity in regions affected by complex electrodynamic effects. These findings lay the foundation for subsequent studies of coupling processes in the ionospheric E‐F region. Key Points: Innovatively modified Ca+ Doppler lidar achieves ion temperature measurements in the challenging E‐F regionThe temperatures detected by lidar in the E region are reasonable, and exploratory temperatures in the F region are also obtainedThe discussion on optimizing the Ca+ Doppler lidars provides valuable guidance for temperature measurements in the E‐F region up to 300 km [ABSTRACT FROM AUTHOR]

Frequency comb spectroscopy and field-resolved broadband absorption spectroscopy are promising techniques for rapid, precise, and sensitive detection of short-lived atmospheric pollutants on-site. Enhancing detection sensitivity in absorption spectroscopy hinges on bright sources that cover molecular resonances and fast signal modulation techniques to implement lock-in detection schemes efficiently. Yb:YAG thin-disk lasers, combined with optical parametric oscillators (OPOs), present a compelling solution to fulfill these requirements. In this work, we report on a bright OPO pumped using a Yb:YAG thin-disk Kerr-lens mode-locked oscillator delivering 2.8 W, 114 fs pulses at 2.06 μm with an averaged energy of 90 nJ. The OPO cavity operates at 30.9 MHz repetition rate—twice the repetition rate of the pump laser—allowing for a broadband, efficient, and dispersion-free modulation of the OPO output pulses at a 15.45 MHz rate. With 13% optical-to-optical conversion efficiency and a high-frequency intra-cavity modulation, this scalable scheme holds promise to advance the detection sensitivity and frontiers of field-resolved spectroscopy. [ABSTRACT FROM AUTHOR]

The synthesis of 2D MoWS2 nanosheets involved the liquid-phase exfoliation technique was explored in this paper. The nonlinear optical response of MoWS2 was characterized in the 1 µm wavelength range, and its suitability as a saturable absorber (SA) was confirmed. Experimental demonstrations were conducted by using MoWS2 as an SA in an idler-resonant intracavity KTA optical parametric oscillator (OPO) driven by a dual-loss-modulated Q-switched and mode-locked (QML) YVO4/Nd:YVO4 laser with an acousto-optic modulator (AOM). By appropriately tuning the pump power and the AOM repetition rate, the Q-switched envelope pulse widths for the signal and idler waves could be significantly reduced to be shorter than the cavity round-trip transit time, i.e., the interval between two neighboring mode-locking pulses. Consequently, this enabled the generation of sub-nanosecond single mode-locking pulses with a low repetition rate, high pulse energy, and remarkable stability. With a repetition rate of 1 kHz and maximal pulse energies of 318 µJ and 169 µJ, respectively, sub-nanosecond single mode-locking pulses of the signal and idler waves were generated. The theoretical model was established using coupled rate equations with a Gaussian spatial distribution approximation. The numerical simulation results for generating sub-nanosecond single mode-locking pulses for the signal and idler waves within their respective Q-switched envelopes aligned fundamentally with the experimental results, proving that MoWS2 can be a potential nanomaterial for further optoelectronic applications. [ABSTRACT FROM AUTHOR]

The VUv Laser for Considering Astrophysical and Isolated Molecules (VULCAIMs) setup [Harper et al., Phys. Chem. Chem. Phys. 24, 2777 (2022)] integrates a narrow-bandwidth tunable vacuum ultraviolet (VUV) and extreme ultraviolet (XUV) nanosecond-pulsed laser system (6–16 eV) and a photoelectron spectrometer, designed for recording high-spectral-resolution (rotationally resolved) photoelectron spectra of gas-phase free radicals. This approach usually needs beforehand medium-resolution synchrotron data to guide the selection of specific spectral regions to be investigated at higher resolution with the VULCAIM setup. We present an upgraded version of the VUV laser system integrating an optical parametric oscillator for continuously scanned medium-resolution measurements (< 3 cm−1) across the whole VUV and XUV spectral ranges. This innovation enables broader coverage without the need to access synchrotron facilities. Furthermore, rapid mode switching allows for maintaining optimized radical production conditions from mid-resolution to high-resolution operation mode, enhancing spectroscopy capabilities significantly. The new capabilities of the VULCAIM setup are illustrated on two showcases of photoionization studies: the nitric oxide (NO) stable molecular species and the benzyl (C6H5CH2) free radical produced by pyrolysis. [ABSTRACT FROM AUTHOR]

In this paper, we demonstrate a tunable mid-infrared (mid-IR) optical parametric oscillator (OPO) using an MgO: PPLN crystal with a polarization period of 29.8 μm, which was end-pumped by a 1064 nm electro-optic cavity-dumped all-solid-state laser (1064 nm EOCD-laser) with a pulse repetition frequency range of 100 Hz to 1 kHz. Thanks to the use of 808 nm pulsed laser diode (LD) side-pumping Nd: YAG crystal, transverse electro-optic modulating (TEOM) MgO: LN crystal, and birefringent crystal (BC) filtering in the 1064 nm cavity-dumped cavity, both the 1064 nm EOCD-laser and the idler light output by the OPO exhibited high peak power and low peak-to-peak instability in both pulse width and single pulse energy. By combining temperature tuning of the MgO: PPLN crystal from 30 °C to 200 °C, wavelength tuning of the idler light from 3705.2 to 3424.3 nm was achieved. For the first time, a pulsed idler light at 3705.2 nm with a high peak power of 1.224 MW, a narrow pulse width of 4.97 ns, and an optical-to-optical (1064 nm to 3705.2 nm) conversion efficiency of 38.1% was obtained, corresponding to a tuning temperature of 30 °C and a pulse repetition frequency of 100 Hz. The peak-to-peak instability for both pulse width and single pulse energy was only ± 1.04% and ± 1.41%, respectively. [ABSTRACT FROM AUTHOR]

The linear radical cation of cyanoacetylene, HC3N+ (2Π), is not only of astrophysical interest, being the, so far undetected, cationic counterpart of the abundant cyanoaceteylene, but also of fundamental spectroscopic interest due to its strong spin–orbit and Renner–Teller interactions. Here, we present the first broadband vibrational action spectroscopic investigation of this ion through the infrared pre-dissociation (IRPD) method using a Ne tag. Experiments have been performed using the FELion cryogenic ion-trap instrument in combination with the FELIX free-electron lasers and a Laservision optical parametric oscillator/optical parametric amplifier system. The vibronic splitting patterns of the three interacting bending modes (ν5, ν6, ν7), ranging from 180 to 1600 cm−1, could be fully resolved revealing several bands that were previously unobserved. The associated Renner–Teller and intermode coupling constants have been determined by fitting an effective Hamiltonian to the experimental data, and the obtained spectroscopic constants are in reasonable agreement with previous photoelectron spectroscopy (PES) studies and ab initio calculations on the HC3N+ ion. The influence of the attached Ne atom on the infrared spectrum has been investigated by ab initio calculations at the RCCSD(T)-F12a level of theory, which strongly indicates that the discrepancies between the IRPD and PES data are a result of the effects of the Ne attachment. [ABSTRACT FROM AUTHOR]

The linear radical cation of cyanoacetylene, HC3N+ (2Π), is not only of astrophysical interest, being the, so far undetected, cationic counterpart of the abundant cyanoaceteylene, but also of fundamental spectroscopic interest due to its strong spin–orbit and Renner–Teller interactions. Here, we present the first broadband vibrational action spectroscopic investigation of this ion through the infrared pre-dissociation (IRPD) method using a Ne tag. Experiments have been performed using the FELion cryogenic ion-trap instrument in combination with the FELIX free-electron lasers and a Laservision optical parametric oscillator/optical parametric amplifier system. The vibronic splitting patterns of the three interacting bending modes (ν5, ν6, ν7), ranging from 180 to 1600 cm−1, could be fully resolved revealing several bands that were previously unobserved. The associated Renner–Teller and intermode coupling constants have been determined by fitting an effective Hamiltonian to the experimental data, and the obtained spectroscopic constants are in reasonable agreement with previous photoelectron spectroscopy (PES) studies and ab initio calculations on the HC3N+ ion. The influence of the attached Ne atom on the infrared spectrum has been investigated by ab initio calculations at the RCCSD(T)-F12a level of theory, which strongly indicates that the discrepancies between the IRPD and PES data are a result of the effects of the Ne attachment. [ABSTRACT FROM AUTHOR]

We demonstrate coherent anti-Stokes Raman scattering (CARS) microscopy with 1089 foci, enabled by a high repetition rate amplified oscillator and an optical parametric amplifier. We employ a camera as a multichannel detector to acquire and separate the signals from the foci, rather than using the camera image itself. This allows us to retain the insensitivity of the imaging to scattering afforded by the non-linear excitation point-spread function, which is the hallmark of point-scanning techniques. We show frame rates of 0.3 Hz for a megapixel CARS image, limited by the camera used. The laser source and corresponding CARS signal allows for at least 1000 times higher speed, and using faster cameras would allow acquiring at that speed, opening a perspective to megapixel CARS imaging with a frame rate of more than 100 Hz. [ABSTRACT FROM AUTHOR]

In this paper, we report a new model for passively Q-switched intracavity optical parametric oscillators (IC-OPOs), using Cr:YAG as a Q-switch crystal. The model considers the effects of thermalization in the Nd:YAG laser crystal, excited state absorption in the Cr:YAG saturable absorber, nonlinear loss due to pump depletion in the nonlinear crystal, the thermal lens effect and the mode overlap of the fields within the nonlinear crystal. The calculated pulse width for the 1,064 nm pump light was 6.2 ns compared to the experimental result of 6 ns, while the signal wave was calculated to have a pulse width of 1.75 ns compared to the experimental result of 2 ns. The model is shown to accurately calculate both the temporal and output power characteristics of the IC-OPO, which has not been previously reported to the best of our knowledge. [ABSTRACT FROM AUTHOR]

Coherent anti‐Stokes Raman scattering microscopy probing two independently selectable vibrational frequencies across the vibrational spectrum is demonstrated. A one‐box femtosecond laser source provides three synchronised 100–200 fs pulses of 77 MHz repetition rate, one at a fixed wavelength of 1025 nm from an Yb oscillator and two independently tuneable ones, over 680–960 nm and 960–1300 nm, respectively, from two optically synchronised parametric oscillators. Combined with spectral focusing, the source allows addressing the fingerprint, cell silent and C–H stretch vibrational regions simultaneously, avoiding the motion artefacts seen in sequential imaging. We demonstrate the microscopy method on water/heavy water/oil emulsions, plastic beads and deuterated lipids inside cells. [ABSTRACT FROM AUTHOR]

Ta2NiS5 nanosheets were fabricated and analyzed for their microstructures and nonlinear optical responses. As a saturable absorber (SA), Ta2NiS5 was integrated into an idler-resonant KTiOAsO4 (KTA)-based intracavity optical parametric oscillator (IOPO) pumped by a dual-loss-modulated Q-switched YVO4/Nd:YVO4 laser. At an incident pump power of 18.9 W and an acousto-optic modulator (AOM) modulation rate of 4 kHz, the maximum output powers of 467 mW for the signal wave and 228 mW for the idler wave were achieved, corresponding to an overall optical-to-optical conversion efficiency of 3.68%. Remarkably, the shortest measured pulse widths of 872 ps for the signal wave and 2.86 ns for the idler wave were obtained, corresponding to the highest peak powers of 392 kW and 57.6 kW for the signal and idler waves, respectively. In comparison to the IOPO pumped by a singly Q-switched YVO4/Nd:YVO4 laser (SIOPO) with an AOM, the IOPO pumped by a doubly Q-switched YVO4/Nd:YVO4 laser (DIOPO) with an AOM and a Ta2NiS5 SA can generate signal and idler waves with significantly shorter pulse widths and higher peak powers. Additionally, the coupled rate equations for the idler-resonant DIOPO were given. The numerical simulations exhibited remarkable consistency with the experimental results. [ABSTRACT FROM AUTHOR]

Non-Hermitian systems around exceptional points (EPs) demonstrate increased sensitivity as the EP order increases. We propose a protocol for constructing a reconfigurable non-Hermitian system consisting of three coupled optical parametric oscillators (OPOs) and demonstrate its enhanced sensitivity around EPs. The coupled OPO system exhibits reconfigurable high-order EPs and corresponding-order enhanced sensitivity (i.e. fourth and sixth order) when it is subjected to pump modulation. Furthermore, the coupled OPO system can synthesize directly a Floquet non-Hermitian system by introducing periodic pump modulation, and can achieve a tunable second-order Floquet EP without periodic modulation of the coupling rates. The convenient flexibility of the coupled OPO system allows it to operate at EPs of different orders and customize a Floquet EP by manipulating the pump parameters. Our protocol can thus contribute to the development of high-performance sensors and precision measurement devices by exploring the unique features of non-Hermitian systems around various EPs. [ABSTRACT FROM AUTHOR]

The ability to confine and guide wave makes topological physics a promising platform for large local field enhancement and strong scattering immunity, which enables efficient nonlinear processes. In this research, we employ a mirror-stacking approach to achieve resonance through two distinct frequency localized states (LSs) in one-dimensional topological circuits, introducing a novel method for validating topological states to facilitate harmonic enhancement. Experimental results reveal that the harmonic wave power increases significantly, by two orders of magnitude, when both the fundamental and harmonic waves are in LSs, in contrast to cases where only one wave is localized. The conversion efficiency is 15.7 times that when the fundamental wave is in a localized state and the harmonic is in a transmission mode. This method, leveraging double-resonance in topological LSs, not only advances harmonic generation in topolectrical circuits but also opens up possibilities for innovative applications in the broader field of photonic technology. This paper presents a study on topologically enhanced third harmonic generation within resonant nonlinear topolectrical circuits. The authors demonstrate that the implementation of a mirror-stacking approach in one-dimensional topological circuits enables achieving significant harmonic wave power increase, leading to efficient nonlinear processes. [ABSTRACT FROM AUTHOR]

This work is devoted to the development of a compact source of coherent radiation with frequency-energy characteristics and a spectral generation range that allows remote determination of background concentrations of greenhouse gases in the atmosphere. The aim of this work was to create a frequency parametric converter based on ZGP, pumped by Ho:YAG laser radiation. For use as a source in a mobile lidar for remote determination of the concentration of greenhouse gases in the atmosphere. In the course of the research, a layout of an Optical parametric oscillator OPO based on a ZGP crystal with Ho:YAG laser radiation pumping was developed. The system's continuous failure-free operation time was 1.5 h at a pulse repetition rate of 10 kHz and a pulse energy of the generated radiation of 0.08 mJ. The tuning range of the OPO was from 3.3 to 5 μιτι when using a Lyot filter. The losses from the average generation power when the Lyot filter was introduced into the resonator were 30%. At the same time, it was possible to achieve a linewidth of the generated radiation of 0.7 nm. The divergence of the generated radiation did not exceed 1.5 mrad.The absorption spectrum of gases CO2, CH4, N2O, CO in a gas cell was simulated for the entire generation range of the ZnGeP2-based OPO. As a result of the simulation, the most intense absorption lines of gases CO2, CH4, N2O, CO in the OPO tuning range were revealed, the central wavelengths of the absorption lines and their spectral width were determined. [ABSTRACT FROM AUTHOR]

We present the results of experimental study of nondegenerate spontaneous parametric downconversion in a single-resonance optical parametric oscillator with two PPKTP crystals. The possibility of generating narrow-band polarization-entangled photons, one of which has a wavelength of 580 nm and a spectral width of 8.0 ± 1.5 MHz, has been shown. This makes such a source of photon pairs compatible with solid-state quantum memory based on a Y2SiO5 : Eu3+ crystal, which is promising for quantum repeaters. [ABSTRACT FROM AUTHOR]

The multicomponent gas analyzer has a wide range of applications, such as environmental monitoring, chemical reaction and industrial process control, accident prevention, exploration in the oil and gas industries, and biomedicine. Laser photoacoustic spectroscopy is the universal method for analyzing gaseous impurities due to its high selectivity, sensitivity, and fast response. This paper presents an automated gas analysis system based on the combined optical parametric oscillators tuning from 2.5 to 10.8 µm. The full width at half maximum of the spectral line is approximately 5.5 ± 0.5 cm–1 in the range from 2.5 to 4.5 μm and approximately 2 ± 0.5 cm–1 in the range from 4.5 to 10.8 μm. Using software installed on the control computer, the controller performs all necessary operations, including pumping, analysis, and removal of gas samples in the measuring complex. The paper presents experimentally recorded absorption spectra of gas mixtures of CO, CO2, and CH4 obtained using a differential photoacoustic detector. [ABSTRACT FROM AUTHOR]

We analyse a system of a singly resonant optical parametric oscillator for a second order nonlinear material. First, we show that the dynamics of the resonating cavity signal mode can be expressed by a Stuart–Landau oscillator, for a certain pumping powers close to the threshold. Second, we couple two optical parametric oscillators indirectly via a cold resonator. When the condition of a weak coupling is satisfied, the limit-cycle of each oscillator is unaltered, and the system is described by a coupled phase oscillator model (Kuramoto model), where a frequency synchronization of the two oscillators occurs at a critical coupling constant. [ABSTRACT FROM AUTHOR]

While nano-crystalline diamond (NCD) is a promising engineering composite material for its unique mechanical properties, achieving the ultrahigh surface quality of NCD-based components through conventional grinding and polishing is challenging due to its exceptional hardness and brittleness. In the present work, we experimentally investigate the nanosecond laser ablation-induced graphitization characteristics of NCD, which provides a critical pretreatment method of NCD for realizing its superlative surface finish. Specifically, systematic experimental investigations of the nanosecond pulsed laser ablation of NCD are carried out, in which the characteristics of graphitization are qualitatively characterized by the Raman spectroscopy detection of the ablated area of the microhole and microgroove. Subsequently, the influence of laser processing parameters on the degree and morphological characteristics of graphitization is evaluated based on experimental data and related interpretation, from which optimized parameters for maximizing the graphitization of NCD are then identified. The findings reported in the current work provide guidance for promoting the machinability of NCD via laser irradiation-induced surface modification. [ABSTRACT FROM AUTHOR]

An overview of Optical Parametric Chirped Pulse Amplification (OPCPA) is given as the basis for the next generation of ultra-intense laser systems (> 1 × 10 23 W/cm2). The benefits and drawbacks of OPCPA are discussed to explain the choice behind the decisions for the direction of the Central Laser Facility's (CLF) upcoming Vulcan 20-20 project. A history of OPCPA use at the CLF is described to surmise the foundation of the confidence in this technology for Vulcan 20-20; a 20 PW user facility for high-intensity plasma physics. [ABSTRACT FROM AUTHOR]

Weakly bound CO2-Rg2 trimers are studied by high-resolution (0.002 cm−1) infrared spectroscopy in the region of the CO2 ν3 fundamental band (≈2350 cm−1), using a tunable optical parametric oscillator to probe a pulsed supersonic slit jet expansion with an effective rotational temperature of about 2 K. CO2–Ar2 spectra have been reported previously, but they are extended here to include Rg = Ne, Kr, and Xe as well as new combination and hot bands. For Kr and Xe, a unified scaled parameter scheme is used to account for the many possible isotopic species. Vibrational shifts of CO2-Rg2 trimers are compared to those of CO2-Rg dimers, and in all cases the trimer shifts are slightly more positive (blue-shifted) than expected on the basis of linear extrapolation from the dimer. Combination bands directly measure an intermolecular vibrational mode (the CO2 rock) and give values of about 32.2, 33.8, and 34.7 cm−1 for CO2–Ar2, –Kr2, and –Xe2. Structural parameters derived for CO2-Rg2 trimers are compared with those of CO2-Rg and Rg2 dimers. Spectra of the mixed trimers CO2-Rg-He are also reported. [ABSTRACT FROM AUTHOR]

A single-pump optical parametric amplifier (OPA) is modeled using a p-toluene sulfonate (PTS) filled silicon-based slotted photonic crystal waveguide (SPCW). The PTS-SPCW has CMOS-process compatibility and offers slow-light enhanced nonlinearity of PTS due to extreme optical confinement in SPCW. The adverse effects of two-photon absorption and free carrier absorption are absent in PTS in the standard optical communication window. The coupled nonlinear Schrödinger's equations have been modified to analyze the OPA under slow-light propagation. Performances of the OPA are evaluated in both the high- and low- dispersive zones of the structure. The high dispersive zone exhibits high group indices to the operating waves, leading to a high parametric gain (≈ 31 dB) and high conversion efficiency (≈ 27 dB) utilizing a 350 μ m long PTS-SPCW and a pump power of 65 mW. However, this zone degrades the shape of a ≤ 10 ps pulse due to self-phase and cross-phase modulation. On the other hand, in the low dispersive zone, a similar parametric gain and conversion efficiency (both ≈ 29 dB) are attained utilizing a 1250 μ m long PTS-SPCW and a pump power of 150 mW. Nevertheless, this zone degrades a 5 ps pulse only after a distance of 1500 μ m. The analyses show a 30 nm bandwidth considering a gain above 30 dB. Investigation of the effect of fabrication imperfections shows excellent performance sustainability of the OPA up to a random error of 40 nm. These remarkable performances make this low-powered, small-footprint OPA suitable for achieving tunable optical amplification in photonic integrated circuits. [ABSTRACT FROM AUTHOR]

We report on a nanosecond-pulsed CdSiP2 (CSP) optical parametric oscillator (OPO) pumped by a Q-switched 2.06 µm Ho:LiLuF4 (Ho:LLF) laser in a compact linear cavity with a 10 mm long crystal. Utilizing a non-collinear type-I phase-matching configuration, the OPO achieved an average output power exceeding 3 W in the mid-IR region with good beam quality. The idler and signal waves can be tuned in a wide range of 3.5–4.7 µm by pump tilt and crystal rotation.

The rotationally resolved infrared (IR) spectrum of the He– H 3 + complex has been measured in a cryogenic ion trap experiment at a nominal temperature of 4 K. Predissociation of the stored complex has been invoked by excitation of the degenerate ν2 mode of the H 3 + sub-unit using a pulsed optical parametric oscillator system. An assignment of the experimental spectrum became possible through one-to-one correlations with bands of the spectrum theoretically predicted in Paper I [Harding et al., J. Chem. Phys. 156, 144307 (2022)]. 19 bands have been assigned and analyzed, and the energy term diagram of the lower states of this floppy molecular complex has been derived from combination differences (CDs) in the experimental spectrum. Ground state combination differences (GSCDs) reveal a large part of the energy term diagram for the He– H 3 + complex in its vibrational ground state, v = 0. Experimental and theoretical term energies agree within experimental accuracy for the rotational fine structure associated with the total angular momentum quantum number J and the parity e/f as well as for the coarse spacing of the lowest K states of the complex. This favorable comparison shows that the potential energy surface (PES) calculated in Paper I is accurate. The barriers between the three equivalent global minima in this PES are relatively low and the He– H 3 + complex is extremely floppy, with nearly unhindered internal rotation of the H 3 + sub-unit. The resulting Coriolis interactions couple the internal and end-over-end rotation of the complex and contribute significantly to the energy terms. They are observed both in experiment and theory and are, e.g., the origin of different rotational constants for states of e and f parity. Also in this respect, experiment and theory agree very well. Despite the assignment and analysis of many bands of the extremely rich IR spectrum of He– H 3 + , higher levels of excitation, including the complex stretching mode, need further attention. [ABSTRACT FROM AUTHOR]

Chirped pulse amplification (CPA) has been a commonly used methodology to obtain powerful ultrashort laser pulses ever since its first demonstration. However, wavelength-tunable CPA systems are much less common. Wavelength-tunable ultrashort and intense laser pulses are desirable in various fields such as nonlinear spectroscopy and optical parametric amplification. In this work, we report a 1720 nm–1800 nm tunable CPA system based on Tm-doped fiber. The tunable CPA system contains a seed laser, a pulse stretcher, two cascaded amplifiers and a pulse compressor. The dispersion-managed seed laser cavity emits wavelength-tunable laser pulses with pulse durations of several ps and spectral widths from 25 nm to 34 nm. After being stretched temporally to tens of ps, the laser pulses are then amplified in two-stage amplifiers and compressed in a Treacy-type compressor. At 1720 nm, the maximum average power of 126 mW is obtained with a pulse duration of 507 fs; at 1800 nm, the maximum average power of 264 mW is obtained with a pulse duration of 294 fs. The pulse repetition rates are around 22.7 MHz. We perform an analysis of the system design based on numerical simulations and go on to suggest further steps for improvement. To the best of our knowledge, this is the first demonstration of a tunable CPA system beyond 1.1 μm. Considering the specific wavelength range, this wavelength-tunable CPA system is highly desirable for biomedical imaging, sensing, and parametric amplifiers. [ABSTRACT FROM AUTHOR]

The gain factor of the optical parametric amplification (OPA) process is known to be negligible in the small scale due to low‐interaction‐medium length. Hence, in the nanoscale, OPA is deemed as infeasible. Therefore, in small‐scale‐integrated optical devices, stimulated‐emission‐based amplifiers (lasers) are employed instead of OPAs. In contrast, the major advantage of OPAs over lasers is that unlike lasers which only provide amplification over a narrow spectral band, OPAs provide high‐gain amplification over a very large, user‐controlled spectral band. In this article, it is shown that OPA can yield wideband high‐gain amplification over a nanoscale beam propagation distance through dispersion engineering. This is achieved by a proper tuning of the pump (source) wave frequency, which can maximize the effective medium nonlinearity by a few orders of magnitude, while concurrently maximizing the intracavity energy density, thereby compensating for the small co‐propagation distance for the input (signal) and pump beams. In this study, it is shown that an input wave can be amplified by a factor 108$\left(10\right)^{8}$ in a nanoscale cavity via precise dispersion engineering. Both empirical and computational formulations are used for the investigation, which display a reasonable agreement. [ABSTRACT FROM AUTHOR]

We demonstrate the generation of broadband tunable and synchronized pulses exceeding the microjoule level using the new concept of Fiber Optical Parametric Chirped-Pulse Oscillation (FOPCPO). The oscillator is based on a collapsed-ends photonic crystal fiber pumped in the normal dispersion regime by an ytterbium fiber laser delivering highly-chirped pulses. The experimental results are compared with the results of numerical simulations and highlight that the feedback ratio appears as a key parameter for optimizing the system's efficiency and dynamics. [ABSTRACT FROM AUTHOR]

We demonstrate an experimental and theoretical comparison of non-oxide LiGaS2, HgGa2S4, and AgGaS2 crystals performance for wavelength conversion into the near and mid-IR range 1.5–8 μm in optical parametric amplifier pumped by Cr:Forsterite laser, delivering 100 fs pulses at 1.24 μm. It is shown that exceptionally high total energy conversion efficiency into the idler (4–5 μm) and signal (1.65–1.8 μm) waves up to 18% can be achieved using the HGS crystal, providing high nonlinearity, while the LGS crystal is more preferable for generating few-cycle mid-IR pulses due its unique dispersive properties. Our source features high peak power in gigawatt regime (0.4–2.4 GW) with pulse duration below 80 fs and optical synchronization with high harmonic generation (HHG) and THz beamlines, which is ideal for pump-probe experiments of nonlinear and strong-field physics. [ABSTRACT FROM AUTHOR]

We describe an efficient long-wave infrared optical parametric oscillator based on ZnGeP2 crystal pumped by a diode-pumped AO Q-switched Ho:YAG laser in this paper. The wavelength of the laser pulse generated by Ho:YAG laser is 2.09- μιτι, and the maximum output average power is 25.3 W at repetition rate of 10 kHz. When pumped by such Ho:YAG laser, the maximum average output power of 0.66 W at 9.8 μ!Γ is achieved, corresponding to slope efficiency of 5.0% and optical efficiency of 2.6%. Furthermore, the beam quality factor of the longwave infrared beam is measured to be approximately 1.3. To the authors' best knowledge, this is the best performance reported for a long-wave infrared ZGP-OPO pumped by a diode-pumped AO Q-switched Ho:YAG laser. [ABSTRACT FROM AUTHOR]

This study's novel 13Ni400 maraging steel parts are additively manufactured through a selective laser melting process. The Taguchi approach is adopted to evaluate the combined influence of process variables (energy density), viz., laser power, layer thickness, hatch spacing, and scan speed, on responses like relative density, microhardness, surface roughness, and tensile strength. The powder and material characterization studies are conducted in terms of an optical microscope, scanning electron microscope (SEM), electron backscatter diffraction (EBSD), X-ray diffraction (XRD), and fractography analysis to explore the pre- and post-fabrication scenarios of the build parts. The consequences of energy density and process variables are studied through meticulous parametric studies. Finally, the optimum level of built parameters is identified and validated by a confirmative test predicting an average error of ~1.80%. This work is proficient in producing defect-free parts with maximum densification and improved mechanical properties for newly developed 13Ni-400 maraging steel by the selective laser melting (SLM) technique. [ABSTRACT FROM AUTHOR]

Precision measurements on molecules in the strong fundamental bands are of great importance. An ac curate mid-infrared light source is a key for these studies. By locking the signal and pump light to an optical frequency comb, a high-precision continu ous-wave optical parametric oscillator source is built, and the mid-infrared frequency drift is deter mined to be less than 1 kHz. As a demonstration, saturated absorption spectroscopy of the R(14) (00011)–(00001) line of 13CO2 is measured, and the transition frequency is determined to be 68786813496(29) kHz. The frequency-stabilized mid-infrared laser source provides an opportunity for precision measurements of molecules in fundamental bands. [ABSTRACT FROM AUTHOR]

In this paper, we present a picosecond pulsed, synchronously pumped optical parametric oscillator producing vortex beam output with tunable wavelengths in the near- to mid-infrared range. The system utilizes a Nd:YVO4 picosecond pulsed solid-state laser emitting at a wavelength of 1.064 µm to pump a Z-shaped, singly resonant OPO which contains a MgO:PPLN crystal with a fan-shaped grating. The wavelength tuning characteristics of the OPO output are examined both as a function of the MgO:PPLN grating period and crystal temperature. The orbital angular momentum of the pump field can be selectively transferred to either the signal or idler fields by appropriately adjusting the location of the MgO:PPLN crystal within the OPO cavity. The maximum output power of the signal and idler vortex fields are 5.12 W and 3.46 W, respectively, for an incident pump power of 19 W. [ABSTRACT FROM AUTHOR]

In this paper, we report a theoretical systematic study of continuous wave intracavity backwards optical parametric oscillators based on periodically poled lithium niobate (PPLN) for mid-infrared (mid-IR) light generation. We study the effects of varying different cavity parameters including nonlinear crystal length, cavity size, pump laser diode spot size, output coupler radius, and cavity loss values on the output power and threshold of the proposed mid-IR laser. The effects of different physical phenomena are included in the model including pump depletion due to the nonlinear conversion process, the thermal lens effect, and mode overlap between the beams in the nonlinear crystal. We show that high output powers in the mid infrared (>500 mW at 3.2 μm) can be achieved with proper cavity design and that a laser threshold with a PPLN as short as 2 cm can be reached. [ABSTRACT FROM AUTHOR]

Quantum optical technologies promise advances in sensing, computing, and communication. A key resource is squeezed light, where quantum noise is redistributed between optical quadratures. We introduce a monolithic, chip-scale platform that exploits the (2) nonlinearity of a thin-film lithium niobate (TFLN) resonator device to efficiently generate squeezed states of light. Our system integrates all essential components--except for the laser and two detectors--on a single chip with an area of one square centimeter, reducing the size, operational complexity, and power consumption associated with conventional setups. Using the balanced homodyne measurement subsystem that we implemented on the same chip, we measure a squeezing of 0.55 decibels and an anti-squeezing of 1.55 decibels. We use 20 milliwatts of input power to generate the parametric oscillator pump field by using second harmonic generation on the same chip. Our work represents a step toward compact and effficient quantum optical systems posed to leverage the rapid advances in integrated nonlinear and quantum photonics. [ABSTRACT FROM AUTHOR]