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Width-increased dual-pump enhanced coherent anti-Stokes Raman spectroscopy (WIDECARS) measurements were used to determine the temperature and major species mole fractions in laminar, premixed, ethylene–air flames operating at atmospheric pressure. Conventional ultrabroadband dye lasers for WIDECARS, which use Pyrromethene dyes, have historically suffered from day-to-day wavelength shifting. To overcome this problem, a new ultrabroadband dye laser was developed in this study to provide a stable wavelength and power generation. A new dye laser pumping scheme and a mixture of Sulforhodamine 640, Kiton Red 620, and Rhodamine 640, was used to generate the desired FWHM ${\sim}{15}\;{\rm nm}$∼15nm (${410}\;{{\rm cm}^{ - 1}}$410cm^−1) bandwidth. The WIDECARS measured mole fraction ratios of ${{\rm CO}_2}$CO_2, CO, and ${{\rm H}_2}$H_2 with ${{\rm N}_2}$N_2 agreed well with chemical equilibrium calculations.

A multispectral imaging system, based on a modified plenoptic camera, is presented. By adding a color filter in the aperture plane of the imaging system, it is possible to simultaneously image multiple discrete colors of light—seven in this design. To develop a measurement system that does not rely on in situ calibrations, each of the optical elements was characterized a priori. For the camera sensor, measurements of the exposure linearity, exposure duration, and quantum efficiency were measured. Additionally, the transmission of the optical filters, both spectral and neutral density, as well as the signal attenuation of the filter holder itself were measured. These measurements result in an instrument that can quantitatively image the emission of seven discrete spectral bands simultaneously. An example application of pyrometry is presented where the emission of a blackbody calibration source with known temperature was imaged. It was determined that by fitting the measured emission at seven wavelengths to Planck’s law of radiation, the temperature could be determined to a mean difference of 0.65ºC across five temperatures from 600° to 1000ºC when compared to the set-point temperature.

A 100 kHz krypton (Kr) tagging velocimetry (KTV) technique was demonstrated in a Mach-6 Ludwieg tube using a burst-mode laser-pumped optical parametric oscillator system. The single-beam KTV scheme at 212 nm produced an insufficient signal in this large hypersonic wind tunnel because of its low Kr seeding (≤5%), low static pressure (∼2.5torr), and long working distance (∼1m). To overcome these issues, a new scheme using two excitation beams was developed to enhance KTV performance. A 355 nm laser beam was combined with the 212 nm beam to promote efficient two-photon Kr excitation at 212 nm, and increase the probability of 2 + 1 resonant-enhanced multiphoton ionization by adding a 355 nm beam. A signal enhancement of approximately six times was obtained. Using this two-excitation beam approach, strong long-lasting KTV was successfully demonstrated at a 100 kHz repetition rate in a Mach-6 flow.

This paper presents a new, to the best of our knowledge, technique to control the flow of electron packets employing a switchable digital metasurface in the terahertz region. The proposed structure can act as a device that converts an electromagnetic (EM) wave into electron packets that can be represented in the form of digital bit sequences at the output. The top layer of the structure controls the intensity of the electron packets while the bottom layer involves the spatial distribution of the information with the help of electrical switching. The electrical switching is achieved with the application of suitable biasing across a vanadium dioxide (VO_2) patch. This approach to the distribution of information helps feed the circuitry of an electronic system as per the requirement using electrical tuning, which is not possible in a conventional antenna system.

A conceptual study has been carried out on laser station networks to enhance Space Situational Awareness and contribute to collision avoidance in the low Earth orbit by high-precision laser tracking of debris objects and momentum transfer via photon pressure from ground-based high-power lasers. Depending on the network size, geographical distribution of stations, orbit parameters, and remaining time to conjunction, multipass irradiation enhances the efficiency of photon momentum coupling by 1–2 orders of magnitude and has the potential to eventually yield a promisingly significant reduction of the collision rate in low Earth orbit.

As the use of X-ray computed tomography (CT) grows in medical diagnosis, so does the concern for the harm a radiation dose can cause and the biological risks it represents. StaticCodeCT is a new low-dose imaging architecture that uses a single-static coded aperture (CA) in a CT gantry. It exploits the highly correlated data in the projection domain to estimate the unobserved measurements on the detector. We previously analyzed the StaticCodeCT system by emulating the effect of the coded mask on experimental CT data. In contrast, this manuscript presents test-bed reconstructions using an experimental cone-beam X-ray CT system with a CA holder. We analyzed the reconstruction quality using three different techniques to manufacture the CAs: metal additive manufacturing, cold casting, and ceramic additive manufacturing. Furthermore, we propose an optimization method to design the CA pattern based on the algorithm developed for the measurement estimation. The obtained results point to the possibility of the real deployment of StaticCodeCT systems in practice.

Manipulating the light scattering direction and enhancing directivity are important research areas in integrated nanophotonic devices. Herein, a novel, to the best of our knowledge, nanoantenna composed of hollow silicon nanoblocks is designed to allow directional emission manipulation. In this device, forward scattering is enhanced and backward scattering is restrained substantially in the visible region. Owing to electric dipole resonance and magnetic dipole resonance in this nanoantenna, Kerker’s type conditions are satisfied, and the directionality of forward scattering G_FB reaches 44.6 dB, indicating good characteristics in manipulating the light scattering direction.

We report on the design, performance, and qualification of the injection laser system designed to deliver joule-level chirped pulse beamlets arranged in dual rectangular beam formats into two main laser amplifier beamlines of the National Ignition Facility. The system is designed to meet the requirements of the Advanced Radiographic Capability upgrade with features that deliver performance, adjustability, and long-term reliability.

Two-dimensional (2D) Rayleigh scattering (RS) imaging at an ultrahigh repetition rate of 100 kHz is demonstrated in non-reacting flows employing a high-energy burst-mode laser system. Image sequences of flow mixture fraction were directly derived from high-speed RS images. Additionally, a 2D instantaneous flow velocity field at 100 kHz was obtained through optical-flow-based analysis of the RS images. In further analysis of both the mixture fraction and flow velocity field, the result for the centerline mixture fraction agreed well with the scaling law. The demonstrated high-speed RS technique in conjunction with optical-flow-based analysis provides non-intrusive, simultaneous measurements of the flow mixing and velocity field, extending the measurement capability of the RS technique to high-speed non-reacting and reacting flows.

In this paper, we report on surface-plasmon-resonance enhancement of the time-dependent reflection changes caused by laser-induced acoustic waves. We measure an enhancement of the reflection changes induced by several acoustical modes, such as longitudinal, quasi-normal, and surface acoustic waves, by a factor of 10–20. We show that the reflection changes induced by the longitudinal and quasi-normal modes are enhanced in the wings of the surface plasmon polariton resonance. The surface acoustic wave-induced reflection changes are enhanced on the peak of this resonance. We attribute the enhanced reflection changes to the longitudinal wave and the quasi-normal mode to a shift in the surface plasmon polariton resonance via acoustically induced electron density changes and via grating geometry changes.

This paper presents successive studies of single-, double-, and triple-layered metasurface-based bandpass filters along with their equivalent circuit modeling and mathematical analyses. A triple-layered bandpass filter operating in the THz region is reported exhibiting flattop passband response while maintaining transmission of more than 95% over the entire passband starting from the design of a single-layered bandpass filter configuration. A stepwise mathematical analysis is carried out for the single-layered structure and compared with the simulation data, where the two results have been found in good agreement. Thereafter, the study is extended for double- and triple-layer bandpass filters. The triple-layered structure offers a very steep transition between passband and stopband with noise-free background, and thereby offers a potential candidate for 6G communication.

Optical diagnostics of gas-phase pressure are relatively unusual. In this work, we demonstrate a novel, rapid, and robust method to use laser-induced grating scattering (LIGS) to derive this property in real time. Previous pressure measurements with LIGS have employed a signal fitting method, but this is relatively time-consuming and requires specialist understanding. In this paper, we directly measure a decay lifetime from a LIGS signal and then employ a calibration surface constructed using a physics-based model to convert this value to pressure. This method was applied to an optically accessible single-cylinder internal combustion engine, yielding an accuracy of better than 10% at all tested conditions above atmospheric pressure. This new approach complements the existing strength of LIGS in precisely and accurately deriving temperature with a simple analysis method, by adding pressure information with a similarly simple method.

10 kHz two-color OH planar laser-induced fluorescence (PLIF) thermometry was demonstrated in both laminar Hencken flames and turbulent premixed jet flames using two injection-seeded optical parametric oscillators (OPOs) pumped by a high-speed three-legged burst-mode laser. The two burst-mode OPOs generate ∼5mJ/pulse at 282 nm and 286 nm to excite the Q_1(5) and Q_1(14) transitions of the A^2Σ^+?X^2Π (1,0) system of OH, respectively. PLIF images were collected simultaneously from each of the two transitions and ratios of intensities from the two images were used to determine local temperatures. Analyses of flame curvature, temperature, and the correlation in time of these two quantities are also discussed. The results from this work are promising for the use of this technique in more complex flow environments and at, potentially, even higher repetition rate.

Nonintrusive three-component (3C) velocity measurements of free jet flows were conducted by stereoscopic picosecond laser electronic excitation tagging (S-PLEET) at 100 kHz. The fundamental frequency of the burst-mode laser at 1064 nm was focused to generate the PLEET signal in a free jet flow. A stereoscopic imaging system was used to capture the PLEET signals. The 3C centroids of the PLEET signal were determined by utilizing simultaneous images from two cameras placed at an angle. The temporal evolutions of the centroids were obtained and used to determine the instantaneous, time-resolved 3C velocities of the flows. The free jets with various inlet pressures of 10–40 bars exhausting into atmospheric pressure air (i.e., underexpanded free jet with large pressure ratios; Reynolds numbers from the jet ranged from 39,000 to 145,000) were measured by S-PLEET. Key 3C turbulent properties of the free jets, including instantaneous and mean velocities, were obtained with an instantaneous measurement uncertainty of about ${\rm{\pm 10}}\;{\rm{m/s}}$, which is about 2% of the highest velocities measured. Computation of higher-order statistics including covariances related to turbulent kinetic energy and the Reynolds stress component was demonstrated. The 3C nonintrusive and unseeded velocimetry technique could provide a new tool for flow property measurements in ground test facilities; the measured high-frequency turbulence properties of free jet flows could be useful for turbulence modeling and validations.

A study of short-gated 10 nanosecond (ns), 100 picosecond (ps), and 100 femtosecond (fs) laser induced breakdown spectroscopy (LIBS) was conducted for fuel-to-air ratio (FAR) measurements in an atmospheric Hencken flame. The intent of the work is to understand which emission lines are available near the optical range in each pulse width regime and which emission ratios may be favorable for generating equivalence ratio calibration curves. The emission spectra in the range of 550–800 nm for ns-LIBS and ps-LIBS are mostly similar with slightly elevated atomic oxygen lines by ps-LIBS. Spectra from fs-LIBS show the lowest continuum background and prominent individual atomic lines, though have significantly weaker ionic emission from nitrogen. A qualitative explanation based on assumed local thermodynamic equilibrium and electron temperatures calculated by the ${{\rm{N}}_{\rm{II}}}({{565}}\;{\rm{nm}})$ and ${{\rm{N}}_{\rm{II}}}({{594}}\;{\rm{nm}})$ emissions is presented. In studying line emission ratios for FAR calculation, it is found that ${{\rm{H}}_\alpha}({{656}}\;{\rm{nm}})/{{\rm{N}}_{\rm{II}}}({{568}}\;{\rm{nm}})$ is best for FAR measurements with ns-LIBS and remains viable for ps-LIBS, while ${{\rm{H}}_\alpha}({{656}}\;{\rm{nm}})/{{\rm{O}}_{\rm I}}({{777}}\;{\rm{nm}})$ is optimal for the ps-LIBS and fs-LIBS cases. Due to low continuum background and short time delay for spectra collection, fs-LIBS is very promising for high-speed FAR measurements using short-gated LIBS.

A compact fiber-coupled hyperspectral imaging sensor (HSIS) operating within the range of ultraviolet to near-infrared (UV–NIR) wavelengths is designed and developed for the remote recording of two-dimensional (2D) spectrally resolved thermal radiation and chemiluminescent emission from ultra-high-temperature ceramics (UHTCs). Using simulations, the entire system is optimized to improve the collection efficiency and minimize aberrations. The design, construction, and characterization of the HSIS sensor are discussed in detail. We present the 2D spectrally resolved measurements of the simultaneous thermal radiation and BO2∗ chemiluminescent emission from a commonly used UHTC (HfB_2-SiC) material under high-heat-flux conditions. Our results show that BO2∗ chemiluminescence corresponds directly to material ablation and can be used to track the formation of the protective heat-resistant glass/oxide layer. Furthermore, the temperature measurements demonstrate the heat distribution properties of the sample and indicate the locations at which BO2∗ chemiluminescence is possible. These results highlight the application prospects of the compact fiber-coupled HSIS for high-temperature material characterization in practical arc-jet facilities with limited optical access.

Femtosecond laser electronic excitation tagging (FLEET) velocimetry was used in the boundary layer of an ogive-cylinder model in a Mach-6 Ludwieg tube. One-dimensional velocity profiles were extracted from the FLEET signal in laminar boundary layers from pure N_2 flows at unit Reynolds numbers ranging from 3.4×10^6/m to3.9×10^6/m. The effects of model tip bluntness and the unit Reynolds number on the velocity profiles were investigated. The challenges and strategies of applying FLEET for direct boundary layer velocity measurement are discussed. The potential of utilizing FLEET velocimetry for understanding the dynamics of laminar and turbulent boundary layers in hypersonic flows is demonstrated.

Small, highly absorbing points are randomly present on the surfaces of the main interferometer optics in Advanced LIGO. The resulting nanometer scale thermo-elastic deformations and substrate lenses from these micron-scale absorbers significantly reduce the sensitivity of the interferometer directly though a reduction in the power-recycling gain and indirect interactions with the feedback control system. We review the expected surface deformation from point absorbers and provide a pedagogical description of the impact on power buildup in second generation gravitational wave detectors (dual-recycled Fabry–Perot Michelson interferometers). This analysis predicts that the power-dependent reduction in interferometer performance will significantly degrade maximum stored power by up to 50% and, hence, limit GW sensitivity, but it suggests system wide corrections that can be implemented in current and future GW detectors. This is particularly pressing given that future GW detectors call for an order of magnitude more stored power than currently used in Advanced LIGO in Observing Run 3. We briefly review strategies to mitigate the effects of point absorbers in current and future GW wave detectors to maximize the success of these enterprises.

The advanced radiographic capability (ARC) laser system, part of the National Ignition Facility (NIF) at Lawrence Livermore National Laboratory, is a short-pulse laser capability integrated into the NIF. The ARC is designed to provide adjustable pulse lengths of ∼1−38ps in four independent beamlets, each with energies up to 1 kJ (depending on pulse duration). A detailed model of the ARC lasers has been developed that predicts the time- and space-resolved focal spots on target for each shot. Measurements made to characterize static and dynamic wavefront characteristics of the ARC are important inputs to the code. Modeling has been validated with measurements of the time-integrated focal spot at the target chamber center (TCC) at low power, and the space-integrated pulse duration at high power, using currently available diagnostics. These simulations indicate that each of the four ARC beamlets achieves a peak intensity on target of up to a few 10^18W/cm^2.

We have developed an SI-traceable narrow-band tunable radiance source based on an optical parametric oscillator (OPO) and an integrating sphere for the calibration of spectroradiometers. The source is calibrated with a reference detector over the ultraviolet/visible spectral range with an uncertainty of <1%. As a case study, a CubeSat spectroradiometer has been calibrated for radiance over its operating range from 370 nm to 480 nm. To validate the results, the instrument has also been calibrated with a traditional setup based on a diffuser and an FEL lamp. Both routes show good agreement within the combined measurement uncertainty. The OPO-based approach could be an interesting alternative to the traditional method, not only because of reduced measurement uncertainty, but also because it directly allows for wavelength calibration and characterization of the instrumental spectral response function and stray light effects, which could reduce calibration time and cost.

In this paper, the effect of jamming in a free-space optical (FSO) communication system that employs optical space shift keying (OSSK) is studied. The optical link suffers from saturated atmospheric turbulence (AT). Hence, the channel fading coefficients follow negative exponential probability density function (PDF). Along with additive Gaussian noise, the jammer, under consideration, is an additional source of noise, and jamming signals also suffer from saturated AT. Thus, the jamming channel also follows the negative exponential PDF. A multiple-input single-output (MISO) FSO system is used to mitigate the effects of jammer and channel fading. Explicitly, we employ a 2×1 MISO-OSSK system for analysis and derive a closed-form expression of bit error rate (BER) of the considered system. Moreover, the jammer’s effect is also studied numerically under the gamma-gamma (GG) fading channel.

Krypton (Kr)-based tagging velocimetry is demonstrated in a Kr/N_2 jet at 100 kHz repetition rate using a custom-built burst-mode laser and optical parametric oscillator (OPO) system. At this repetition rate, the wavelength-tunable, narrow linewidth laser platform can generate up to 7 mJ/pulse at resonant Kr two-photon-excitation wavelengths. Following a comprehensive study, we have identified the 212.56 nm two-photon-excitation transition as ideal for efficient Kr-based velocimetry, producing a long-lived (∼40µs) fluorescence signal from single-laser-pulse tagging that is readily amenable to velocity tracking without the need for a second “read” laser pulse. This long-lived fluorescence signal is found to emanate from N_2—rather than from Kr—following efficient energy transfer. Successful flow velocity tracking is demonstrated at multiple locations in a high-speed Kr/N_2 jet flow. The 100 kHz repetition rate provides the ability to perform time-resolved velocimetry measurements in high-speed and even hypersonic flow environments, where standard velocimetry approaches are insufficient to capture the relevant dynamics.

A high-sensitivity surface plasmon resonance (SPR) sensor is designed and analyzed numerically. The sensor is constructed on the eightfold U-shaped photonic quasi-crystal fiber (PQF) and coated with indium tin oxide (ITO). The coupling between the core mode and surface plasmon polariton mode is enhanced due to shortening of the distance between the core and the ITO layer, so that the PQF-SPR sensor exhibits high refractive index (RI) sensitivity in the near-infrared region. The maximum wavelength sensitivity and the corresponding resolution of this sensor are 42,000 nm/RIU and 2.38×10^−6RIU, respectively. The average wavelength sensitivity is 12,750 nm/RIU in the refractive index range of 1.306–1.386. This advanced sensor is suitable for the determination of RIs in the near-infrared region.

We describe the construction and operation of a large ring laser whose beam paths enclose an area of 6.25m^2. The gyroscopic performance of this large laser interferometer was determined using laser operation at a wavelength of 632.8 nm. The laser cavity Q was inferred to be 1.1×10^12 via a measured ring-down time of 375 µs, and the measured Sagnac frequency is 198.40 Hz due to Earth’s rotation. The measured experimental sensitivity to rotation achieved is 7.9×10^−12rad/s/Hz at an averaging interval of 512 s (being limited primarily by ambient building noise). The observation of microseismic activity in the 200 mHz region as well as local earthquakes is discussed.

In this paper, a study is made of the refractive index structure parameter Cn2, as derived from angle-of-arrival (AOA) measurements made on the beam after propagation along a 16 km slant path across the Chesapeake Bay. These measurements are compared with Cn2 estimates derived from the Navy Atmospheric Vertical Surface Layer Model (NAVSLaM), which are based upon prevailing meteorological conditions. Correlation coefficients for the reported data vary between 0.64 and 0.9. Despite the Chesapeake Bay theoretically being a difficult location for employing a Monin–Obukhov similarity theory-based model such as NAVSLaM, the agreement between the AOA Cn2 measurements and the NAVSLaM Cn2 estimates was, in many cases, good. A possible explanation of this agreement between the modeled and measured Cn2 values is that the large air–water temperature differences encountered provided such strong forcing for the NAVSLaM model that any potential violations of the Monin–Obukhov similarity theory assumptions had only a secondary influence on the Cn2 estimates.

A procedure for timely, accurate, and reproducible alignment of an optical cavity is described.

We present an experimental study in which we compare two different pump–probe setups to generate and detect high-frequency laser-induced ultrasound for the detection of gratings buried underneath optically opaque metal layers. One system is built around a high-fluence, low-repetition-rate femtosecond laser (1 kHz) and the other around a low-fluence, high-repetition-rate femtosecond laser (5.1 MHz). We find that the signal diffracted by the acoustic replica of the grating as a function of pump–probe time delay is very different for the two setups used. We attribute this difference to the presence of a constant background field due to optical scattering by interface roughness. In the low-fluence setup, the optical field diffracted by the acoustic replica is significantly weaker than the background optical field, with which it can destructively or constructively interfere. For the right phase difference between the optical fields, this can lead to a significant “amplification” of the weak field diffracted off the grating-shaped acoustic waves. For the high-fluence system, the situation is reversed because the field diffracted off the acoustic-wave-induced grating is significantly larger than the background optical field. Our measurements show that optical scattering by interface roughness must be taken into account to properly explain experiments on laser-induced ultrasound performed with high-repetition-rate laser systems and can be used to enhance signal strength.

Infrared (IR) images are basically low-contrast in nature; hence, it is essential to enhance the contrast of IR images to facilitate real-life applications. This work proposes a novel adaptive clip-limit-oriented bi-histogram equalization (bi-HE) method for enhancing IR images. HE methods are simple in implementation but often cause over-enhancement due to the presence of long spikes. To reduce long spikes, this work suggests to apply a log-power operation on the histogram, where the log operation reduces the long spikes, and power transformation regains the shape of the histogram. First, a histogram separation point is generated applying the mean of the multi-peaks of the input histogram. After that, an alteration in the input histogram is done using the log-power process. Subsequently, a clipping operation on the altered histogram followed by redistribution of the clipped portion is performed to restrict over-enhancement. Next, the modified histogram is sub-divided using the histogram separation point. Finally, the modified sub-histograms are equalized independently. Simulation results show that the suggested method effectively improves the contrast of IR images. Visual quality evaluations and quantitative assessment demonstrate that the suggested method outperforms the state-of-the-art algorithms.

Photon momentum radiometers measure the force imparted by a reflected laser beam to determine the laser’s optical power. This requires high-accuracy calibration of the force sensors using milligram and microgram mass artifacts. Calibrated test masses can therefore be used to provide traceability of these radiometers to the International System of Units, but low-noise calibration at these mass levels is difficult. Here, we present the improvement in calibration capability that we have gained from implementing a robotic mass delivery system. We quantify this in terms of the specific nuances of force measurements as implemented for laser power metrology.

We investigate microsecond pulse-mode operation of a micro-integrated high-power diode laser based on volume Bragg grating external-cavity feedback around 808 nm. The laser system contains a tapered amplifier consisting of a ridge-waveguide section and a tapered section with separated electrical contacts. Thus, the diode laser system can be pulsed by modulating the injected current either to the ridge waveguide section (I_RW) or to the tapered amplifier section (I_TA). With a trigger signal of a 50 µs pulse width and a 10 kHz repetition rate, comparing the modulation depth, peak output power, beam propagation factor, and spectral bandwidth, we conclude that the pulse-mode operation achieved by modulating the I_TA gives better results than by modulating the I_RW due to the decreased thermal effect. At a constant I_RW of 0.2 A and a modulated I_TA of 6.0 A, 4.3 W of peak output power is obtained with an emission spectral bandwidth with an upper bound of 0.2 nm, and a beam propagation factor in the slow axis, Mslow2, of 2.6 (1/e^2). The modulation depth is almost 100%. The results show that the tapered diode laser system may be a good candidate for microsecond pulse-mode solid-state lasers.

We report a full experimental comparison study on the injection of a Ti:Sa multi-terawatt amplifier chain with a standard 15 fs Ti:Sa oscillator and 35 fs frequency-doubled fiber oscillator. The study highlights that the Ti:Sa oscillator, with high performance in terms of pulse duration and spectral width, can be replaced by the frequency-doubled fiber oscillator to seed Ti:Sa amplifier chains almost without any compromise on the output pulse duration and picosecond contrast. Finally, we demonstrate for the first time to our knowledge a 30 TW and 33 fs Ti:Sa amplifier injected by a fiber oscillator.

This paper describes a novel, to the best of our knowledge, approach to build ultrastable interferometers using commercial mirror mounts anchored in an ultralow expansion (ULE) base. These components will play a critical role in any light particle search (ALPS) and will also be included in ground testing equipment for the upcoming laser interferometer space antenna (LISA) mission. Contrary to the standard ultrastable designs where mirrors are bonded to the spacers, ruling out any later modifications and alignments, our design remains flexible and allows the alignment of optical components at all stages to be optimized and changed. Here we present the dimensional stability and angular stability of two commercial mirror mounts characterized in a cavity setup. The long-term length change in the cavity did not exceed 30 nm and the relative angular stability was within 2 µrad, which meet the requirements for ALPS. We were also able to demonstrate 1pm/Hz length noise stability, which is a critical requirement for various subsystems in LISA. These results have led us to design similar opto-mechanical structures, which will be used in ground verification to test the LISA telescope.

A highly sensitive surface plasmon resonance (SPR) sensor comprising an eccentric core photonic quasi-crystal fiber (PQF) coated with indium tin oxide is designed and numerically analyzed. The novel, to the best of our knowledge, structure with an eccentric core layout and local coating not only strengthens coupling between the core mode and surface plasmon polariton mode but also provides higher refractive index sensitivity in the near-infrared region. Analysis based on the finite element method to assess the performance of the sensor and optimize the structural parameters reveals that the maximum wavelength sensitivity and resolution are 96667 nm/RIU and 1.034×10^−6RIU in the sensing range between 1.380 and 1.413, respectively. Meanwhile, the average sensitivity is enhanced to 25458 nm/RIU. The sensor is expected to have broad applications in environmental monitoring, biochemical sensing, food safety testing, and related applications due to the ultrahigh sensitivity and resolution.

The development of actinic mask metrology tools represents one of the major challenges to be addressed on the roadmap of extreme ultraviolet (EUV) lithography. Technological advancements in EUV lithography result in the possibility to print increasingly fine and highly resolved structures on a silicon wafer; however, the presence of fine-scale defects, interspersed in the printable mask layout, may lead to defective wafer prints. Hence, the development of actinic methods for review of potential defect sites becomes paramount. Here, we report on a ptychographic algorithm that makes use of prior information about the object to be retrieved, generated by means of rigorous computations, to improve the detectability of defects whose dimensions are of the order of the wavelength. The comprehensive study demonstrates that the inclusion of prior information as a regularizer in the ptychographic optimization problem results in a higher reconstruction quality and an improved robustness to noise with respect to the standard ptychographic iterative engine (PIE). We show that the proposed method decreases the number of scan positions necessary to retrieve a high-quality image and relaxes requirements in terms of signal-to-noise ratio (SNR). The results are further compared with state-of-the-art total variation-based ptychographic imaging.

Transmission of intense ultrashort laser pulses through hollow-core fibers (HCFs) is investigated for molecular-tagging velocimetry. A low-vacuumed HCF beam-delivery system is developed to transmit high-peak-power pulses. Vacuum pressure effects on transmission efficiency and nonlinear effects at the fiber output are studied for 100 ps and 100 fs laser beams. With a 0.1 bar vacuum in the fiber, transmission efficiency increases by ∼30%, while spectral broadening is reduced. A 1 m long, 1 mm core metal-dielectric-coated HCF can transmit ∼45  mJ/pulse and ∼2.9  mJ/pulse for 100 ps laser pulses (at 532 nm) and 100 fs laser pulses (at 810 nm), respectively. Proof-of-principle, single-laser-shot, fiber-coupled, ps and fs laser-based, nitrogen electronic-excitation tagging velocimetry is demonstrated in a free jet. Flow velocities are measured at 200 kHz to capture high-frequency flow events.

Developments toward the implementation of a terahertz pulse imaging system within a guided reflectometry configuration are reported. Two photoconductive antennas patterned on the same LT-GaAs active layer in association with a silica pipe hollow-core waveguide allowed us to obtain a guided optics-free imager. Besides working in a pulsed regime, the setup does not require additional optics to focus and couple the terahertz pulses into the waveguide core, simplifying the global implementation in comparison with other reported guided terahertz reflectometry systems. The system is qualified for imaging purposes by means of a 1951 USAF resolution test chart. An image resolution, after a 53 mm propagation length, by about 0.707 LP/mm over the 400–550 GHz integrated frequency band, was obtained, thus providing a promising basis to pursue efforts toward compact guided pulse imagers for sample inspection within the terahertz range.

Hyperspectral imaging for agricultural applications provides a solution for non-destructive, large-area crop monitoring. However, current products are bulky and expensive due to complicated optics and electronics. A linear variable filter was developed for implementation into a prototype hyperspectral imaging camera that demonstrates good spectral performance between 450 and 900 nm. Equipped with a feature extraction and classification algorithm, the proposed system can be used to determine potato plant health with ${\sim}{88}\% $∼88% accuracy. This algorithm was also capable of species identification and is demonstrated as being capable of differentiating between rocket, lettuce, and spinach. Results are promising for an entry-level, low-cost hyperspectral imaging solution for agriculture applications.

A novel compact micro-integrated high-power narrow-linewidth external-cavity diode laser around 808 nm is demonstrated. The laser system contains a tapered amplifier consisting of a ridge-waveguide section and a tapered section with separated electrical contacts. Thus, the injection currents to both sections can be controlled independently. An external volume Bragg grating is utilized for spectral narrowing and stabilization. The diode laser system is integrated on a ${5}\;{\rm mm}\;{\times}\;{13}\;{\rm mm}$5mm×13mm aluminum nitride micro-optical bench on a conduction cooled package mount with a footprint of ${25}\;{\rm mm}\;{\times}\;{25}\;{\rm mm}$25mm×25mm. The diode laser system is characterized by measuring the output power and spectrum with the injection currents to the ridge-waveguide section (${I_\textrm{RW}}$I_RW) and tapered amplifier section (${I_\textrm{TA}}$I_TA) changed in steps of 25 and 50 mA, respectively. At ${I_\textrm{RW}}={200}\;{\rm mA}$I_RW=200mA and ${I_\textrm{TA}}={6.0}\;{\rm A}$I_TA=6.0A, 3.5 W of output power is obtained with an emission spectral linewidth with an upper bound of 6 pm, and a beam propagation factor in the slow axis, ${M^2}$M^2, of 2.6 (${{1/e}^2}$1/e^2). The characterization of the temperature stabilization of the laser system shows an increase of the wavelength at a rate of 6.5 pm/K, typical for the applied volume Bragg grating.

We present an optical architecture for a scanning lidar in which a digital micromirror device (DMD) is placed at an intermediate image plane in a receiver to decouple the trade-offs between scan angle, scan speed, and aperture size of the lidar’s transmitter and receiver. In the architecture, the transmitter with a galvo mirror and the receiver with a DMD scan the horizontal and vertical fields of view, respectively, to enable an increased field of view of 50°, centimeter transmitter beam diameter, and video frame rate range finding captures. We present our optimized system and discuss the adjustable parameter trade-offs.

In the past decade, superconducting nanowire single-photon detectors (SNSPDs) have gradually become an indispensable part of any demanding quantum optics experiment. Until now, most SNSPDs have been coupled to single-mode fibers. SNSPDs coupled to multimode fibers have shown promising efficiencies but have yet to achieve high time resolution. For a number of applications ranging from quantum nano-photonics to bio-optics, high efficiency and high time resolution are desired at the same time. In this paper, we demonstrate the role of polarization on the efficiency of multimode-fiber-coupled detectors and fabricated high-performance 20 µm, 25 µm, and 50 µm diameter detectors targeted for visible, near-infrared, and telecom wavelengths. A custom-built setup was used to simulate realistic experiments with randomized modes in the fiber. We achieved over 80% system efficiency and $ {\lt} {20}\;{\rm ps}$<20ps timing jitter for 20 µm SNSPDs. Also, we realized 70% system efficiency and $ {\lt} {20}\;{\rm ps}$<20ps timing jitter for 50 µm SNSPDs. The high-efficiency multimode-fiber-coupled SNSPDs with unparalleled time resolution will benefit various quantum optics experiments and applications in the future.

Recently, titanium-based nanostructures with high nonlinear optical properties have found use in ultrafast photonic system applications. Here, we report a study of the third-order nonlinear optical property of the ${{\rm CuCo}_{0.5}}{{\rm Ti}_{0.5}}{{\rm O}_2}$CuCo_0.5Ti_0.5O_2 (CCoTO) nanostructure synthesized via a simple chemical route. The 40–70 nm CCoTO nanoparticles with centrosymmetric crystalline structure show strong absorption in the 325–850 nm wavelength range due to the presence of different crystalline phases and surface vacancies. A Z-scan technique is used to study the electronic third-order nonlinearity of the synthesized nanoparticles, where a low-repetition-rate 120 fs laser source is employed to minimize thermal agitation-related nonlinearity. The CCoTO nanoparticles possess high surface defects due to oxygen- and copper-related vacancies, which are able to enhance the exciton oscillator strength resulting from the high value of third-order optical nonlinearity. The estimated values of nonlinear refractive index (${n_2}$n_2) and nonlinear absorption coefficient ($\beta $β) of the CCoTO are $ - {1.24}\; \times \;{{10}^{ - 15}}$−1.24×10^−15 and ${3.79} \times {{10}^{ - 11}}$3.79×10^−11, respectively, under ${188}\,\,{{\rm GW/cm}^2}$188GW/cm^2 incident intensity. The intensity-dependent nonlinear optical property of the synthesized nanoparticles is also studied under different incident laser irradiation (62.7, 93, and ${188}\,\,{{\rm GW/cm}^2}$188GW/cm^2). In the two-photon absorption (TPA)-dominated third-order nonlinear optical process, the values of ${n_2}$n_2 and $\beta $β of CCoTO are increased with intensifying the incident laser irradiation. The obtained high value of third-order optical nonlinearity of the synthesized nanostructure can be exploited in optical power limiters, pulse power reshaping, and optical switching applications.

In this paper, the guiding properties and sensor performance are numerically investigated for a dual-core hexagonal lattice photonic crystal fiber sensor based on surface plasmon resonance (SPR). Gold is used as the active plasmonic material in order to create resonance, and it is placed outside the fiber structure to facilitate the fabrication process. The finite-element method is used to numerically investigate the characteristics of the sensor. By means of wavelength and amplitude interrogation methods, it is found that the proposed sensor shows maximum wavelength sensitivity of 16,000 nm/RIU with $6.25 \times {10^{ - 6}}\,\,{\rm RIU}$6.25×10^−6RIU resolution and amplitude sensitivity of $2255\,\,{{\rm RIU}^{ - 1}}$2255RIU^−1 with $4.40 \times {10^{ - 6}}\,\,{\rm RIU}$4.40×10^−6RIU resolution. The proposed SPR sensor can detect the analyte refractive index ranging from 1.33 to 1.40. This work also includes an investigation of the effect of changing the gold layer thickness, air-hole diameter, and analyte layer on the sensor performance from the optimized design. The proposed sensor could be employed to detect biological and biochemical analytes because of its simple design and promising results.

The optical properties of symmetric split-ring/ring dimer (SRRD) nanostructures composed of a small nanoring surrounded by an Ag splitting nanoring with a larger diameter are calculated theoretically. The apparent asymmetric Fano line shape in the spectra is related to fast switching of the bonding modes between the split-ring plasmon and ring dipole. The influence of the dimensions of the SRRD nanostructures on the spectral positions and intensity of Fano resonance is studied, and the asymmetric Fano line shape can be flexibly adjusted by varying the geometric parameters. In addition, relatively simple SRRD nanostructures have the same overall sensing figures of merit as conventional nanoparticles, thus rendering them suitable for high-performance optical sensors.

We demonstrate an active Sagnac ring interferometer that operates on the previously unexploited 3s_2→2p_6 (611.8 nm), 3s_2→2p_7 (604.6 nm), and 3s_2→2p_8 (593.9 nm) neon transitions, in a helium–neon gain medium. The cavity was constructed using state-of-the-art ion-beam sputtered, ultralow-loss supermirrors designed to yield greater transmission loss at lower optical frequency, which partially compensates for the gain differential across the three transitions. For an optimized cavity fill of 0.3 mbar partial pressure of neon (50% Ne20 and 50% Ne22) and a total gas pressure of 2 mbar, for laser operation at 611.8 nm, the cavity Q is 1.2×10^11, having a cold cavity ringdown time of 38 μs. The laser yielded a stable Sagnac frequency of 117.4 Hz due to the Earth’s rotation. The usable gyroscopic sensitivity is determined to be 8.8×10^−9  rad/s for a measurement time of 128 s.

Two-photon-absorption laser-induced fluorescence of Kr was explored using both nanosecond- and femtosecond-duration laser excitation sources. Fluorescence signals following two-photon excitation at two wavelengths (212.56 nm and 214.77 nm) were compared while varying laser pulse duration, energy, and excitation wavelength as well as pressure and Kr mole fraction in mixtures with nitrogen. Our findings show that stronger fluorescence was observed when the excitation wavelength was tuned to 212.56 nm, regardless of the excitation-pulse duration. Moreover, an approximate 100-fold signal enhancement from nanosecond excitation (∼3  mJ/pulse, 10 ns duration) was observed as compared to femtosecond excitation (∼6  μJ/pulse, 90 fs duration).

A sensing device composed of an eccentric core photonic quasi-crystal fiber based on surface plasmon resonance is designed using indium tin oxide (ITO) as the sensitive materials. The ITO film is deposited on the outside surface of the fiber to excite plasmonic interactions and facilitate refractive index (RI) detection. This eccentric core structure makes the evanescent field coupled effectively with analyte to achieve higher sensitivity. The influence of RI and structural parameters of different analytes on sensor performance was calculated by the finite-element method. In the analyte RI range between 1.33 and 1.39, the wavelength sensitivity reaches 21,100 nm/RIU, and the average sensitivity of 8750 nm/RIU is achieved at a resolution of 4.739×10^−6  RIU. The sensor has large potential in the detection of unknown RI analytes in the near-infrared region.

This paper demonstrated the nanosecond pulse laser operation at 1.55 and 2 μm wavelength regions using a newly develop chromium-doped fiber (CrDF) as a saturable absorber (SA) to convert efficiently continuous-wave laser operation to nanosecond pulse laser operation. The laser uses an erbium-doped fiber (EDF) and thulium-doped fiber as the gain medium. A piece of 10 cm long CrDF was integrated into both laser cavities to generate nanosecond pulse laser operation. In 1.55 region generation, an additional single-mode fiber (SMF) 100 m long was added into the EDF laser cavity. Stable pulse generation occurred at a repetition rate of 1 MHz with a pulse width of 432 ns and a signal-to-noise ratio (SNR) of 66 dB. The highest peak power of 24 mW was obtained at 142 mW pump power. In 2 μm region generation, the obtained repetition rate was 10 MHz with a pulse width and SNR of 59 ns and 41 dB, respectively. The highest peak power was only 8.3 mW. By looking into the findings, the newly developed CrDF SA has a potential to be further enhanced toward better generation of ultrashort pulse fiber lasers.

A bimetal-coated single-polarization photonic crystal fiber (PCF) filter based on surface plasmon resonance (SPR) with a liquid-filled structure is designed and calculated by the finite element method (FEM). The filter has many excellent properties. The y-polarized and x-polarized modes can simultaneously filter at 1310 nm and 1560 nm with unwanted losses 544.3 dB/cm and 147.3 dB/cm, respectively, corresponding to polarized losses as low as 12.3 dB/cm and 24.0 dB/cm. The filtering range can be tuned by adjusting the diameter of the outer air holes (d_1), the diameter of the inner air holes (d_2), and liquid refractive index n. The filtering ranges of x-polarization and y-polarization are 1550–1990 nm and 1310–1830 nm, respectively. The crosstalk (CT) values are 462.0 dB and −107.1  dB and corresponding available bandwidths are 224 nm and 504 nm at 1310 nm and 1560 nm, respectively.

We present a novel compressive spectral imaging technique that attains spatially resolved ultraspectral resolution. The technique employs a multiscale sampling technique based on the Hadamard basis for the single pixel hyperspectral imager. The proposed multiscale sampling method offers high-quality images at a low compression ratio while also facilitating a preview image at a lower resolution by using the fast Hadamard transform.