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We demonstrate the scanning and control of the carrier-envelope phases (CEPs) of two adjacent spectral components totally spanning more than one-octave in the short-wave infrared (SWIR) wavelength region by operating two individual acousto-optic programmable dispersive filters (AOPDFs) applied to each of the two spectral components. The total CEP shift of the synthesized sub-cycle pulse composed of the two spectral components is controlled with simultaneous scans of the two CEPs. The resultant error of the controlled CEP was 642 mrad, so that this technique is useful for searching zero CEP of the synthesized pulse with the maximum field amplitude. In addition, we conduct a closed feedback loop to compensate for the CEP fluctuation by using the two AOPDFs together. As a result, we succeed to reduce the rms error of the CEP from 399 mrad to 237 mrad.

Fully coherent, soft X-ray attosecond pulses are now available through high-order harmonic generation (HHG); however, the output energy is insufficient for various applications, such as attosecond-scale soft X-ray nonlinear experiments, the seeding of soft X-ray free-electron lasers, attosecond-pump-attosecond-probe spectroscopies, and single-shot imaging. In this paper, we combine a newly developed TW class mid-infrared femtosecond laser and a loose focusing geometry for HHG. A soft X-ray harmonic beam up to the water window region is demonstrated, which is more than 100 times intense compared to previous works. We achieve a high conversion efficiency, low beam divergence and a significantly reduced medium gas pressure. As the first application, we demonstrate near edge X-ray absorption fine structure experiments with clear fine absorption spectra near the K- and L-edges observed. The robust energy scaling method on HHG opens the door for demonstrating single-shot absorption spectrum and live-cell imaging with a femtosecond time resolution. While high harmonic x-ray sources are well established sources for ultrafast spectroscopy, the decrease in efficiency towards higher energies limits their application. Here, a loose-focused, TW mid-IR laser is used to generate high harmonic soft x-rays with pulse energies of a few nJ in the water window and easy energy scaling.

By combining the dual-chirped optical parametric amplification and two kinds of nonlinear crystal (type-I BiBO and type-I MgO), a one-octave bandwidth (1.45 μm – 3 μm), carrier-to-envelope phase (CEP) stable infrared (IR) laser pulses have been achieved. Our approach will generate several tens of millijoule, single-cycle MIR pulse by taking advantage of a few hundred mJ pump energy and a bulk compressor.

Based on the dual-chirped optical parametric amplification and type-I BiB$_3$O$_6$(BiBO) crystals, the generation of $>$100 mJ, 10.4 fs, 10 Hz, carrier-to-envelope phase (CEP)-stable laser pulses, which are centered at 1.7 $μ$m, is demonstrated; it produces a peak power of 10 TW. CEP-dependent high harmonic generation is implemented to confirm the sub-two-cycle pulse duration and CEP stabilization of infrared (IR) laser pulses. As far as we know, the obtained pulse energy and peak power represent the highest values for sub-two-cycle CEP-stable IR optical parametric amplification. Additionally, the prospects of achieving high-energy water window isolated attosecond pulses via our developed laser source are discussed., 4 pages, 4 figures

By employing the dual-chirped optical parametric amplification and type-I BiBO crystals, an over 100 mJ, 10.4 fs, 10 Hz, carrier-to-envelope phase (CEP) stable laser pulses centered at 1.7 μm is achieved, which results in a peak power of 10 TW. In addition, the sub-two-cycle pulse duration and CEP stabilization are identified by the CEP-dependent high harmonic generation via a loosely focused geometry.

By using a dual-chirped optical parametric amplification (DC-OPA) method and employing type-I BiBO crystal, we obtained 102 mJ infrared pulses with spectrum centered at 1.7 µm and pulse duration 10.7 fs after compression.

An intense isolated attosecond pulse (226-as 0.24-μJ) is generated and characterized by waveform synthesizer and attosecond streaking measurement. High power waveform synthesis and streaking measurement under a low laser repetition rate is groundbreakingly implemented.

We found that tropone dications (C7H7O2+) created by the carbon KLL normal Auger decay undergo nonradiative decays via 10-102 dicationic states in the time scale of 102 fs using surface hopping nonadiabatic reaction dynamics simulations.

We report a 226-as 0.24 uJ isolated attosecond pulse generation and characterization by waveform synthesizer and attosecond streaking measurement. Pumping waveform synthesis and streaking measurement are successfully achieved under a low laser repetition rate condition.

We report on the generation of 52 mJ mid-infrared pulses at the center wavelength of 1.7 μm using a BiBO dual-chirped optical parametric amplification scheme (DC-OPA). Pulse compression down to 9.8 fs duration achieved after DC-OPA indicates a peak power of 5.3 TW, which will reach 10 TW peak power by using the whole energy of our available pump laser.

High-energy infrared (IR) femtosecond laser sources are important for applications in ultrafast and strong-field laser science; thus, considerable effort has recently been made to develop such laser systems. In this paper, we review our recent work on developing TW-class mid-infrared (MIR) femtosecond laser pulses in the 1–4 $\mu$ m region using a dual-chirped optical parametric amplification (DC-OPA) method. By employing a Ti:sapphire laser with sub-joule energy to pump the DC-OPA system, MIR femtosecond pulses with 100-mJ-class energy are demonstrated. Efficient energy scalability and flexible wavelength tunability in DC-OPA are confirmed experimentally. Different features of DC-OPA from those of conventional OPA and narrow-band pumped optical parametric chirped pulse amplification (OPCPA) are observed. By precisely optimizing the chirps of the seed and pump pulses in the DC-OPA system, bandwidth narrowing of amplified pulses can be minimized in an energy-scaling strategy. Moreover, DC-OPA can be universally employed for the energy scaling of near-IR, MIR, and far-IR pulses, regardless of the type of nonlinear crystal, and is helpful for efficiently generating few-cycle carrier-envelope phase stable IR pulses with TW-class peak power.

We analyze how optical distortions in deep imaging or dense scattering media influence three-dimensional interferometric temporal focusing (3D-ITF) imaging, and derive the distorted point spread function (PSF) and optical transfer function (OTF). Upon this, we find that 3D-ITF microscopy is less affected by optical distortions in terms of spatial resolution, artifacts and sectioning ability. Temporal focusing (TF) illumination supports a robust spatial modulation in 3D-ITF microscopy with distorted optics. As the modulation spatial frequencies are unique, they offer a redundancy in 3D-ITF microscopy. The redundancy in the spatial frequency of 3D-ITF images compensates for the loss of spatial frequency caused by the optical distortion in the emission OTF. The redundancy recovers the high spatial frequencies to prevent the degradation of spatial resolution. Moreover, the redundancy recovers the distortion in the emission OTF spectrum, which causes distorted shapes in the PSF such as side lobes and double peaks. Thus, there is a relatively lossless OTF spectrum in 3D-ITF compared to TF, and this leads to better trade-off between remaining noise artifacts and resolution after the Wiener filter correction.

The bottleneck for an attosecond science experiment is concluded to be the lack of a high-peak-power isolated attosecond pulse source. Therefore, currently, generating an intense attosecond pulse would be one of the highest priority goals. In this paper, we review a TW-class parallel three-channel waveform synthesizer for generating a gigawatt-scale soft-x-ray isolated attosecond pulse (IAP) using high-order harmonics generation (HHG). Simultaneously, using several stabilization methods, namely, the low-repetition-rate laser carrier-envelope phase stabilization, Mach-Zehnder interferometer, balanced optical cross-correlator, and beam-pointing stabilizer, we demonstrate a stable 50-mJ three-channel optical-waveform synthesizer with a peak power at the multi-TW level. This optical-waveform synthesizer is capable of creating a stable intense optical field for generating an intense continuum harmonic beam thanks to the successful stabilization of all the parameters. Furthermore, the precision control of shot-to-shot reproducible synthesized waveforms is achieved. Through the HHG process employing a loose-focusing geometry, an intense shot-to-shot stable supercontinuum (50-70 eV) is generated in an argon gas cell. This continuum spectrum supports an IAP with a transform-limited duration of 170 as and a submicrojoule pulse energy, which allows the generation of a GW-scale IAP. Another supercontinuum in the soft-x-ray region with higher photon energy of approximately 100-130 eV is also generated in neon gas from the synthesizer. The transform-limited pulse duration is 106 as. According to this work, the enhancement of HHG output through optimized waveform synthesis is experimentally proved. The high-energy multicycle pulse with 10-Hz repetition rate is proved to have the same controllability for optimized waveform synthesis for HHG as few- or subcycle pulses from a 1-kHz laser., Comment: 21 pages, 10 figures

A GW-scale isolated attosecond pulse is demonstrated by a fully stabilized 50-mJ three-channel waveform synthesizers. Isolated pulse duration with 213-as, 0.24-μJ is experimentally characterized by the FROG-CRAB method with a 10-Hz repetition rate.

Multi-photon holographic patterned illumination using temporal focusing (TF) pulses provides 10 μm multi-spots with an axial confinement of 5 μm, enabling parallel photo-stimulation of multi-target cells in three dimensions. However, interference fringes and speckles degrade the uniformity of the spots, causing spatio-temporal fluctuations in photoactivation. Here, we demonstrate fringe- and speckle-free holographic patterned illumination using multifocal time-multiplexed (TM) TF pulses even when the multi-spots overlap spatially. The uniform patterned illumination enabled the expansion of the field-of-view of TM-TF microscopy by more than fivefold and enhanced the axial resolution to 1.3 μm.

Powerful and stable attosecond pulse sources have the potential for wide application in ultrafast science. For this purpose, we have produced a soft X-ray supercontinuum with a pulse energy of 0.24 µJ using high-order harmonics from a multi-terawatt, 10 Hz, three-channel waveform synthesizer [Sci. Adv. 6, eaay2802 (2020)STAMCV1468-699610.1126/sciadv.aay2802]. Here, we report an attosecond streaking scheme that is designed to measure this isolated attosecond pulse at a low-repetition rate. We retrieved a pulse duration of 226 attoseconds (as), demonstrating the realization of 1.1 gigawatt isolated as pulses on a tabletop, which compares favorably to an X-ray free-electron laser in a large facility.

High-order harmonic generation (HHG) is currently utilized for developing compact table-top radiation sources to provide highly coherent extreme ultraviolet (XUV) and soft X-ray pulses; however, the low repetition rate of fundamental lasers, which is typically in the multi-kHz range, restricts the area of application for such HHG-based radiation sources. Here, we demonstrate a novel method for realizing a MHz-repetition-rate coherent XUV light source by utilizing intracavity HHG in a mode-locked oscillator with an Yb:YAG thin disk laser medium and a 100-m-long ring cavity. We have successfully implemented HHG by introducing two different rare gases into two separate foci and picking up each HH beam. Owing to the two different HH beams generated from one cavity, this XUV light source will open a new route to performing a time-resolved measurement with an XUV-pump and XUV-probe scheme at a MHz-repetition rate with a femtosecond resolution., Extreme ultraviolet: generating coherent pulses inside a laser A compact table-top laser system developed by researchers in Japan can generate extreme ultraviolet radiation (XUV) for ultrafast spectroscopy. Coherent XUV pulses are used to accurately measure data on electronic transitions in atoms and molecules, however they can usually only be generated via synchrotron radiation from large particle accelerators. A possible route to generating XUV on a smaller lab scale is to direct high-order harmonic pulses from a femtosecond laser onto a gas. Katsumi Midorikawa at the RIKEN Center for Advanced Photonics in Wako and co-workers have developed a novel method where the gas targets are actually placed inside the laser cavity. By using two different gases, they can simultaneously generate an XUV pump and a probe, opening a route to very accurate timing of atomic measurements, perhaps resolving events as short as a few femtoseconds.

Isolated attosecond pulses can be generated by the polarization gating method, for which the gating time window and the polarization direction are key parameters. In this work, we propose methods to characterize these parameters with an imaging polarimeter based on the division of the focal plane in a single-shot manner. The gating time window and the polarization direction can be characterized using the degree of linear polarization and the angle of linear polarization, respectively. Spatially resolved evaluation of gating parameters is important for generating high-intensity isolated attosecond pulses. The robust generation of isolated attosecond pulses by evaluating the gating parameters with the proposed method will enable us to perform the attosecond-pump and attosecond-probe of electron dynamics in atoms and molecules.

We report on the generation of 103 mJ mid-infrared pulses at 1.7 pm using a BBO dual-chirped optical parametric amplification scheme (DC-OPA) and discuss the octave-spanning DC-OPA by using the dual pumping scheme.

We developed a high power storage ring oscillator using a Yb:YAG thin-disk gain medium pumped with 969nm absorption line. The intra-cavity average and peak power of 1kW and 200MW were attained, respectively at 14MHz operation. © 2020 The Author(s)

We demonstrate a technique to stabilize a Mach Zehnder Interferometer (MZI) including an AOPDF in each interferometer arm, which is utilized for compensating for the dispersion of an over-octave shortwave-infrared spectrum ranging from 0.9 to 2.4 µm. The relative phase jitter was estimated to be 130 mrad. This scheme was adopted in the OPA system generating 4.4 fs (0.73 cycles) pulses at 1.8 µm.

Nano-joule class water-window high-order harmonic generation under a neutralmedium condition is presented. The maximum harmonic photon energy reaches 360 eV with 3.5-nJ/shot in the water-window region.

Science advances 6(16), eaay2802 - (2020). doi:10.1126/sciadv.aay2802, A stable 50-mJ three-channel optical waveform synthesizer is demonstrated and used to reproducibly generate a high-order harmonic supercontinuum in the soft x-ray region. This synthesizer is composed of pump pulses from a 10-Hz repetition-rate Ti:sapphire pump laser and signal and idler pulses from an infrared two-stage optical parametric amplifier driven by this pump laser. With full active stabilization of all relative time delays, relative phases, and the carrier-envelope phase, a shot-to-shot stable intense continuum harmonic spectrum is obtained around 60 eV with pulse energy above 0.24 μJ. The peak power of the soft x-ray continuum is evaluated to be beyond 1 GW with a 170-as transform limit duration. We found a characteristic delay dependence of the multicycle waveform synthesizer and established its control scheme. Compared with the one-color case, we experimentally observe an enhancement of the cutoff spectrum intensity by one to two orders of magnitude using three-color waveform synthesis., Published by Assoc., Washington, DC [u.a.]

An attosecond pulse train consisting of ~210 as pulses is characterized by interferometric autocorrelation measurements of dissociative ionization of C2H2. The selective C-C bond breaking of C2H2+ by the 7th harmonic is identified.

Cancer cells undergo dramatic morphology changes when migrating in confined spaces narrower than their diameter during metastasis, and thus it is necessary to understand the deformation mechanism and associated molecular events in order to study tumor progression. To this end, we propose a new biochip with three-dimensional (3D) polymer nanostructures in a closed glass microfluidic chip. "Ship-in-a-bottle" femtosecond laser processing is an exclusive technique to flexibly create 3D small details in biochips. The wavefront correction by the spatial light modulator significantly improves the fabrication resolution of this technique. The device could then accommodate defect-free 3D biomimetic nanoconfigurations for the evaluation of prostate cancer cell migration in confined spaces. Specifically, polymeric channels with widths of ∼900 nm, which is more than one order of magnitude smaller than the cell size, are integrated by femtosecond laser inside glass channels. The cells are responsive to an in-channel gradient of epidermal growth factor and can migrate a distance greater than 20 μm. After migration, the cells suffer partial cytokinesis, followed by fusion of the divided parts back into single cell bodies.

Few–cycle short–wave infrared (SWIR) pulses are useful tools for research on strong–field physics and nonlinear optics. Here we demonstrate the amplification of sub–cycle pulses in the SWIR region by using a cascaded BBO–based optical parametric amplifier (OPA) chain. By virtue of the tailored wavelength of the pump pulse of 708 nm, we successfully obtained a gain bandwidth of more than one octave for a BBO crystal. The division and synthesis of the spectral components of the pulse in a Mach–Zehnder–type interferometer set in front of the final amplifier enabled us to control the dispersion of each spectral component using an acousto–optic programmable dispersive filter inserted in each arm of the interferometer. As a result, we successfully generated 0.73–optical–cycle pulses at 1.8 μm with a pulse energy of 32 μJ., Short-wavelength infrared pulses are important for applications in strong field physics and nonlinear optics. Here the authors show multi-stage optical parametric amplification of sub-cycle SWIR pulses with carrier-envelope phase stability.

Expansion of the wavelength range for an ultrafast laser is an important ingredient for extending its range of applications. Conventionally, optical parametric amplification (OPA) has been employed to expand the laser wavelength to the infrared (IR) region. However, the achievable pulse energy and peak power have been limited to the mJ and the GW level, respectively. A major difficulty in the further energy scaling of OPA results from a lack of suitable large nonlinear crystals. Here, we circumvent this difficulty by employing a dual-chirped optical parametric amplification (DC-OPA) scheme. We successfully generate a multi-TW IR femtosecond laser pulse with an energy of 100 mJ order, which is higher than that reported in previous works. We also obtain excellent energy scaling ability, ultrashort pulses, flexiable wavelength tunability, and high-energy stability, which prove that DC-OPA is a superior method for the energy scaling of IR pulses to the 10 J/PW level.

Wavefront distortion in temporal focusing microscopy (TFM) results in a distorted temporal profile of the excitation pulses owing to spatio-temporal coupling. Since the pulse duration is dramatically changed in the excitation volume, it is difficult to correct the temporal profile for a thick sample. Here, we demonstrate adaptive optics (AO) correction in a thick sample. We apply structured illumination microscopy (SIM) to an AO correction in wide-field TFM to decrease the change in the pulse duration in the signal detection volume. The AO correction with SIM was very successful in a thick sample for which AO correction with TFM failed.

We report on efficient terahertz-wave generation in organic and inorganic crystals by nonlinear wavelength conversion approach using a 3.3 μm femtosecond pulse laser. Experimental results reveal the relation between pump power and terahertz-wave output power, which is proportional to the square of the pump power at the range of mega- to tera-watt cm−2 class even if the pump wavelength is different. Damage threshold of organic and inorganic crystals are recorded 0.6 and 18 tera-watt cm−2 by reducing several undesirable nonlinear optical effects using mid-infrared source.

By performing delay scans of two replicas of a few-pulse attosecond pulse train (APT), we investigated two-photon ionization/dissociation processes of C 2 H 2 . The correlation time of the C + yield is determined to be 300 as, which is, to the best of our knowledge, the shortest correlation time ever obtained in the delay-scan measurement of two APTs. We also extracted the contribution of the resonant excitation from the ground state to a specific excited state of C 2 H 2 + leading to C–C bond breaking by performing Fourier analyses of the yield and angular distribution of the C H + fragment ions, which are also generated within 300 as.

Temporal focusing (TF) microscopy has a trade-off between temporal resolution, optical sectioning capability, and field of view. To improve this trade-off, we demonstrate time-multiplexed multi-line temporal focusing (TM-ML-TF) microscopy, which combines the time-multiplexed TF technique with multi-line focusing using a digital micromirror device. Compared with those for TF microscopy, the optical sectioning capability and the signal-to-background ratio were improved by factors of 2.5 and 4.17, respectively. In addition, by applying post-processing for structured illumination microscopy to TM-ML-TF microscopy, the optical sectioning capability and the signal-to-background ratio were further enhanced by factors of 1.2 and 4.63, respectively.

In our recent study [Commun. Phys. 3, 92 (2020)], we have developed an approach for energy-scaling of high-order harmonic generation in water-window region under neutral-medium condition. More specifically, we obtained nanojoule-class water-window soft x-ray harmonic beam under phase match condition. It has been achieved by combining a newly developed terawatt-class mid-infrared femtosecond laser and a loose focusing geometry for high-order harmonic generation. The generated beam is more than 100 times intense compared to previously reported results. The experimental setup included two key parts: terawatt mid-infrared femtosecond driving laser [ Sci. Rep. 8, 7692 (2018)] and specially designed gas cell. Despite the dramatic drop in the optimal gas pressure due to loose focusing geometry, it still reached 1 bar level for helium. Moreover, faster leaking speed caused by larger pinhole size of the gas cell made the use of a normal gas cell impossible. Thus, we have designed a double-structured pulsed-gas cell with a differential pumping system, which enabled providing sufficiently high gas pressure. Moreover, it allowed reducing gas consumption significantly. Robust energy-scalable apparatus for high-order harmonic generation developed in in this study will enable the generation of over tens nanojoule water-window attosecond pulses in the nearest future., 10 pages, 8 figures

We theoretically study two-electron dynamics in a wave packet consisting of low-lying doubly excited states of helium, using an attosecond single-color XUV pump–XUV probe scheme. By solving the time-dependent Schrodinger equation in the hyperspherical coordinates, we analyze an ionization plus excitation process followed by a fluorescence emission. Pump–probe delay time dependence of the transition probabilities, and hence the fluorescence signal, is proved to unravel the bending vibrational motion of the two electrons with the nucleus at the center. Such a motion having an analog to that of a floppy triatomic molecule is the true feature of the electron correlation during temporal evolution of an intrashell two-electron wave packet.

We present an energy-scaling experiment on a femtosecond infrared pulse using dual-chirped optical parametric amplification (DC-OPA). A total output energy exceeding 100 mJ with 36-fs pulse duration was achieved in the infrared region, which is the highest energy ever reported for an ultrafast optical parametric amplifier scheme. We also discuss the generation of high-energy 15–30–THz pulses through difference frequency generation between chirped signal and idler pulses based on DC-OPA. By manipulating the phase of a seed pulse in the DC-OPA system, the spectral phase of a THz pulse can be indirectly controlled precisely, which is very helpful for compressing THz pulses.