This PDF file contains the front matter associated with SPIE Proceedings Volume 12869, including the Title Page, Copyright information, Table of Contents, and Conference Committee information.

Ultrabroadband Electro-Optic Sampling (EOS) with few-cycle optical pulses is known to be an exceptionally sensitive technique to detect electric field amplitudes. By combining this method with dual-comb spectroscopy and with a new class of ultrafast lasers, we perform high-resolution (10-80 MHz, 0.0003-0.0027 cm-1) spectroscopic measurements across the whole frequency range of 1.5 to 45 THz (6.6–200 μm), excluding the strongly absorbing Reststrahlen band of lattice resonances at 4.5–9 THz, with an instantaneous spectral coverage exceeding an octave (e.g., 9–22 μm). As a pump source, we use a pair of mutually coherent low-noise frequency combs centered at 2.35 μm produced by mode-locked solid-state Cr:ZnS lasers. To produce a molecular ‘sensing’ comb in the long-wave infrared region, one of the two driving combs is frequency down-converted via Intrapulse Difference Frequency Generation (IDFG) in ZGP or GaSe nonlinear crystals. The second driving comb is frequency doubled in a GaSe crystal to produce a near-IR comb for EOS. A low intensity and phase noise of our dual-comb system allows capturing a vast amount of comb-mode resolved (mode spacing 80 MHz) spectral information (⪆200,000 comb lines) at up to a video rate of 69 Hz. This result was also facilitated by high IDFG conversion efficiency (e.g., ⪆10% in ZGP crystal). Our long-wavelength IR measurements with low-pressure gases: ethanol, isoprene, and dimethyl sulfide reveal spectroscopic features that had never been explored before.

Quantum Cascade Lasers (QCLs) have immense potential for generating chip-scale frequency combs in the mid-infrared and terahertz spectral regions. In this work, we demonstrate the formation of frequency combs within ring terahertz QCLs using optical injection from a Distributed Feedback (DFB) laser. By carefully selecting a DFB design frequency that aligns with the ring cavity modes (around 3.3 THz) and employing a bus waveguide for light injection, we show that combs can be selectively formed and controlled within the ring cavity. Numerical modeling suggests that the observed comb formation is frequency-modulated in nature, with the optical injection acting as a trigger. Furthermore, we demonstrate the ring cavity's ability to function as a filter, a feature that could hold significant value for terahertz photonic integrated circuits. Our findings highlight the promise of waveguide couplers as a robust approach for injecting and extracting radiation from ring terahertz comb and offer exciting possibilities for generation of new comb states in the terahertz domain, including frequency-modulated waves, solitons, and more.

We present a Geometric Phase (GP)-based Sagnac Anti-Resonant Ring (ARR) interferometer mirror (GP-mirror) for achieving tunable optimum output coupling in Continuous Wave (CW) Doubly Resonant Optical parametric oscillator (DRO). The DRO is designed using a nonlinear crystal MgO: PPsLT of 30 mm length and a grating period of 7.97 μm with a GP mirror in one arm of the standing wave cavity. The GP mirror is constructed using a quarter wave-plate (λ/4), half wave plate (λ/2), and quarter wave-plate(λ/4) at +45◦, θ, -45◦ with respect to vertical polarization, respectively. The DRO output transmission can be varied continuously from 0.6% to 50%, attaining optimum output coupling of 1.4% for maximum power extraction of 2.45 W when pumped with an incident power of 5 W at 47◦C crystal temperature at signal and idler wavelength of 1054 nm and 1074 nm, respectively. The maximum pump depletion of 89% is obtained with a conversion efficiency of 49%. The transmission through a GP-based mirror delivers the tunable optimum output power across the tuning wavelength range ⪆ 90 nm. This showcased GP-mirror concept presents an avenue for enhancing the capabilities and management of coherent sources adjustable across various spectral ranges and across all time scales, ranging from continuous-wave to ultrafast femtosecond domains.

We present our latest results in power scaling of Midwave-Infrared (MWIR) Optical Parametric Oscillators (OPOs) based on a Zinc Germanium Phosphide (ZGP) crystal, utilizing a single oscillator fiber laser as pump source. To obtain a compact and complexity-reduced pump source emitting at ≥ 2.09 μm, a Q-switched Tm³⁺:Ho³⁺- codoped fiber laser was developed. Based on this pump source at an emission wavelength of 2.1 μm, we achieved an MWIR output power of 12.2W with pulse energies of up to 270 μJ and a conversion efficiency exceeding 43 %. This result exceeds the published power records of ZGP-based OPOs pumped by 2 μm Q-switched fiber lasers by 50 % and sets a new benchmark for average power scaling and pulse energy of Q-switched pump sources.

We present a Ho³⁺:YAG laser source and use it to pump a linear ZGP OPO with a novel design intended to improve the mode matching properties of the resonator. Beam quality measurements are used to evaluate the performance of the novel design in comparison with a conventional linear resonator. Operated at 25 kHz repetition rate, the Ho³⁺:YAG laser delivers 2.2 mJ, 20 ns Q-switched pulses. This results in a pulse peak power of 108 kW while the average output power is 58W. In the optimal ZGP OPO configuration, 14.1W of signal and idler output power are achieved with a conversion efficiency of 49.8 % with respect to the absorbed pump power. A clearly improved beam quality of 2.1 and 3.3 (2.4 and 3.5) in the x- and y-axis of the signal (idler) beam compared to the conventional linear resonator is shown.

Entangled photon pairs generated by a low-power continuous-wave laser could replicate pulsed laser-based tabletop spectroscopy by taking advantage of the inherent quantum correlations between the photons. Much of the current work in the thin-film lithium niobate platform has focused on infrared wavelengths, leaving shorter wavelengths still a largely unexplored space, particularly for spectroscopy. In this work, we have fabricated periodically poled lithium niobate nanophotonic waveguides for entangled photon generation through spontaneous parametric downconversion with a visible pump (406 nm). Characterization of the waveguided pair source confirms the spectral and temporal correlations of energy-time entangled photons with an on-chip pair generation efficiency of (2.3 ± 0.5) × 1011 pairs/s/mW, brightness of (1.6 ± 0.3) × 109 pairs/s/mW/nm, and two-photon interference visibility greater than 99%. With the same material platform, we have also demonstrated second harmonic generation with on-chip powers up to 30 μW and wavelengths as low as 355 nm, demonstrating lithium niobate’s potential for ultraviolet nonlinear photonics and frequency doubling in the UV-A spectral region. Through design of larger cross-section waveguides, we have also explored how variations in the lithium niobate thin film thickness can affect quasi-phase matching. To date, this is the first reported demonstration of periodically poled lithium niobate nanophotonic waveguides for spontaneous parametric downconversion at a fully visible pump wavelength (406 nm) as well as second harmonic generation in the UV (355 nm). Future work towards fully on-chip spectroscopy will explore integrating an on-chip Mach-Zehnder interferometer with the entangled photon source.

In this work, a high-power laser source with single-mode fiber output in the green spectral range is presented. A ridge waveguide laser with a Distributed Bragg-Reflector (DBR-RWL) and a Tapered Amplifier (TPA) are used as a pump source for a Ridge Waveguide Periodically Poled Lithium Niobate (RW-PPLN) crystal. The whole setup fits into a butterfly housing with a footprint of only 76 mm × 44 mm. At an emission wavelength of 532 nm, an optical output power of hundreds of milliwatt in a single spectral mode with a spectral width of the order of 1 MHz is achieved.

A large wavelength tuning range MgO-doped Periodically Poled Lithium Niobate (PPLN) ridge waveguide is fabricated. Using the iterative domino algorithm, an engineered Quasi Phase Matching (QPM) structure has been implemented to the ridge waveguide, which forms seven wavelength conversion peaks. Each designed conversion peak has equally nonlinear strength and 5nm wavelength separation, locates from 1530 nm to 1560 nm at 40 deg. C. Combined with temperature adjustment between 15 to 60 deg. C, which could tune each phase matching peak for more than 5 nm, full C band tuning range is achieved with high conversion efficiency. Under CW 5.5W single frequency C band input, 3.7W is coupled to the waveguide, and 2.5W SHG is generated.

First reported in 2006 and scaled to long and practical lengths in 2008, semiconductor core optical fibers have matured from basic material and fiber fabrication explorations to a diverse range of practical applications. The ability to bring many on-chip optoelectronic functions inside an optical fiber offers many benefits. This paper begins with a brief historical review of semiconductor fibers, the principal fiber fabrication approaches employed, and the range of material system realized. From there, the nonlinear properties and approaches to their optimization will be discussed along with a range of nonlinear in-fiber devices that have been reported in both telecom and mid-infrared spectral regions. Lastly, on-going challenges and musings on future semiconductor fiber materials, devices, and performance will be made leveraging their significant benefits in terms of their flexibility, power handling, wavelength coverage, and general ease of use over competing fiber and on-chip platforms.

Truly portable supercontinuum sources with high spectral bandwidths are poised to advance applications such as medical imaging, chemical sensing, or light detection and ranging. Yet, limited efficiencies of conventional Supercontinuum Generation (SCG) schemes typically require relatively high pulse energies from bulky ultrafast lasers. We discuss a commercially emerging approach to SCG based on Patterned Sign-alternating Dispersion (PSD) waveguide chips. It is based on alternately subjecting femtosecond seed laser pulses to normal and anomalous dispersion regimes in a highly controlled fashion. PSD waveguides decrease input power requirements down to factors on the order of 1/1000 as compared to other approaches and imply a disruptive reduction in power consumption, size, and costs of required seed laser light sources. We illustrate the real-world performance of PSD waveguide chips operating in tandem with ultra-compact femtosecond fiber lasers, and give an illustrative example of portable near-infrared absorption spectroscopy.

In this paper, we describe picosecond, nonlinear optical experiments with Orientation-Patterned Gallium Phosphide (OPGaP) crystals as a precursor to the development of a solid-state Lidar that can operate in the Long Wave Infrared (LWIR) waveband (7.5-14 μm). An Optical Parametric Oscillator (OPO) is used to compare the performance of OPGaP fabricated on gallium phosphide versus a gallium arsenide substrate. Both materials provide a viable route to generate high peak power, short duration laser pulses in the LWIR waveband. We then demonstrate that OPGaP can be used for up-conversion from the LWIR into the silicon detector waveband. Finally, parametric generation in OPGaP with picosecond pulses is studied and we discuss how it can be used to generate a seed beam for a parametric amplifier.

The field of Nonlinear Optics (NLO), launched about 60 years ago, has gained considerable momentum over the past two decades, resulting in an enormous growth in NLO publications for a wide range of material categories, including bulk materials, 0D-1D-2D materials, metamaterials, fiber waveguiding materials, on-chip waveguiding materials, and hybrid waveguiding systems. However, a convenient summary of NLO data collected since 2000 for these different material types has been lacking and would be a valuable resource for researchers in the field. Here, we present a new set of data tables showcasing a representative list of NLO properties taken from the literature since 2000 on the above-mentioned material categories. Furthermore, we provide best practices for performing and reporting NLO experiments. These best practices underpin the selection process that we used for including papers in the tables, and also form the foundation for a more adequate comparison, interpretation, and use of the NLO parameters published today and those that will be published in the future.

We review the phase-matching properties of AgGa1–xInxSe2 for second-harmonic generation of a CO2 laser at 10.7186–9.2714 μm. The refined Sellmeier equations for AgInSe2 coupled with our previously published Sellmeier equations for AgGaSe2 are found to reproduce well the critical phase-matching conditions at 10.5910–9.2820 μm thus far published in the literature. In addition, these Sellmeier equations are used to clarify the reason for the discrepancy between the measured and calculated 90° phase-matching conditions at 10.6964–9.2714 μm.

We report on a Raman laser emitting in the yellow spectral range using a CO₂-filled hollow-core photonic crystal fiber. Taking advantage of a state-of-art inhibited-coupling hollow-core photonic crystal fibre, exhibiting minimum transmission loss of approximately 1 dB/km in the 500-600 nm region, we were able to develop an extremely compact and simple yellow-Raman laser scheme, allowing to emit as much as 60 mW of average power at the 574.5 nm wavelength while using a compact, microchip laser as a pump source. This solution provides an innovative and scalable alternative for the other yellow laser schemes, which are of high demand in the field of biophotonics due to their effective interaction with hemoglobin and melanin.

For many years, the KGW Raman crystal has been widely used as a Raman gain medium for lasers in the visible spectrum. This paper presents recent advancements in SWIR Raman lasers, successfully implementing the KGW crystal as the gain medium in the SWIR spectral range. The KGW Raman gain coefficient is inversely proportional to the wavelength, potentially lowering the efficacy for longer wavelengths. However, the high damage threshold (exceeding 10 GW/cm²), a decent thermal conductivity coefficient as well as a highly integrated scattering cross-section effectively overcome this challenge. This paper summarizes results of different Tm based/KGW Raman lasers in external cavity configurations. Due to the KGW bi-axial properties, the Raman laser emits two discrete shifted wavelengths. The first system used a Tm:YLF pump laser and was actively Q-switched, producing short pulses of 5.4 ns. The system was the first demonstration of SWIR Raman lasing using a KGW gain medium. The second configuration used a Tm:YAP pump source and was successfully passively Q-switched using a Cr:ZnS SA resulting in output energies of 340 μJ/pulse and 450 μJ/pulse for the respective Raman wavelengths. The third Raman laser achieved a record maximum energy per pulse of 2.08 mJ for the 901 cm⁻¹ Stokes shift utilizing a passively Q-switched Tm:YLF pump laser. To the best of our knowledge, these results present a successful demonstration of SWIR Raman conversion using KGW as the Raman gain medium, along with significant advancements in terms of conversion efficiencies and energy per pulse.

We have generated a visible laser by second harmonic generation from a pulsed Cascaded Raman fiber Lasers (CRFL) continuously tunable in 1060nm-1600nm, using type-I LBO. To eliminate the requirement of precise synchronization and control, we employed a passive Q-switching mechanism for the Yb laser pumping the Raman module. The pump is made continuously tunable in Yb-band with wavelength dependent feedback in the Q-switched cavity ensuring continuous wavelength tunability of generated Raman Stokes. We utilized a large mode-area amplifier to amply pulse-energy without introducing temporal instability and optimized Raman module for efficient pump conversion. We demonstrated a widely tunable visible laser with approximately μJ pulse-energy and approximately 20 − 65kHz repetition-rate, 40-200ns pulse duration. This is the first demonstration of a high pulse energy nanosecond laser continuously tunable in 530nm-600nm making it a versatile laser source for numerous biomedical applications. The wavelength tunable range can be extended to 700nm by utilizing type-II LBO.

We report on high average-power, high-energy picosecond fourth-harmonic generation in LBO. The first stages of a Yb:YAG laser chain operating at 1 kHz repetition rate generate few-picosecond 220 mJ chirped pulses at 1030 nm fundamental wavelength. They are frequency-converted in a cascade of three LBO crystals to generate the second-, third-, and fourth harmonics at 515 nm, 343 nm and 257 nm respectively. Crystals thicknesses and angular phase matching detuning were calculated as a function of pulse duration through broadband nonlinear optical numerical simulations. Last crystal is both conduction-cooled on edge and surface-cooled at center through forced-air flow to mitigate heating due to nonlinear absorption in the deep-UV and reduce temperature gradients. Chirped-pulse duration was experimentally adjusted to achieve stable 20% overall conversion efficiency. Near-field beam profiles were continuously recorded at 10 Hz, for all four wavelengths involved, together with corresponding energies, showing no significant beam degradation over 50 hours. Temperatures of the two last crystals were monitored and will help optimize surface cooling for future power ramping-up.

High power Continuous-Wave (CW) DUV lasers are required for high-resolution laser-based angle-resolved photoemission spectroscopy. This technique provides direct observations of band structures and is utilized to study quantum solid states. We realized a high-power 213 nm coherent light source based on fourth harmonic generation of an 852 nm laser for this purpose. Because we have placed importance on its reliability and long-term operation, we use a home-made nonlinear element and a Voice Coil Motor (VCM) cavity locker. We obtained a highest laser power of more than 270 mW and kept the laser power at 50 mW for long-period operation.

We present a nanosecond-pulsed 655 nm laser source based on frequency-doubling a Raman-shifted fiber laser. At a repetition rate of 1.5 MHz, the source generates an average power of 3.3 W, corresponding to a pulse energy of 2.2 μJ, with a pulse duration of 1.8 ns. The fundamental Raman-shifted fiber laser operating at 1310 nm has a novel configuration where the first Raman shift is performed in an Yb-doped fiber amplifier and the second Raman shift is performed in a phosphosilicate fiber. Both Raman shifting stages are seeded with narrow linewidth CW signals, enabling the temporal properties of an amplified 1064 nm modulated laser diode to be transferred to narrow-band light at 1310 nm with very high conversion efficiency. The resulting micro-Joule-level, nanosecond pulses at 1310 nm are frequency-doubled to 655 nm in a double LBO crystal setup with a conversion efficiency of 51%. The multi-Watt, micro-Joule-level red pulses have near diffraction limited beam quality (M² ≤ 1.04), making this source ideally suited to biomedical imaging applications such as super-resolution and photoacoustic microscopy.

The ultraviolet (UV) wavelengths are gaining attention in various applications including lithography, imaging, and spectroscopy due to their high photon energy and high spatial resolution. However, the strong UV absorption has required specialized optics for beam shaping and wavefront manipulation of the UV. In this paper, a novel beam shaping of UV is demonstrated by manipulating the wavefront of a near-infrared (NIR, λ=800 nm) driving laser in harmonic generation. The preservation of spatiotemporal coherence in harmonic generation allows the transfer of the spatial beam distribution from the IR driver to the UV harmonics. To separate the UV beam from the strong NIR background, a non-collinear harmonic generation configuration is employed. By using quartz and MgO nonlinear medium, the pattern of 2nd harmonic UV (λ=400 nm) and 3rd harmonic deep-UV (λ=266 nm) waves were manipulated. Our technique allows the wavefront control of UV laser beams in UV optical metrology and patterning.

Efficiencies of nonlinear optical-to-terahertz (THz) conversion below one percent remain a limiting factor for applications of multicycle THz radiation like THz-driven acceleration and inspired the use of multi-line pump spectra. To overcome the difficulty of phase stabilization of multiple narrowband sources required by the multi-line approach, we exploit its temporal analog, i.e., regular pulse trains with THz repetition rate, in which the THz waves generated by rectifying the individual pulses add coherently. The optical setup producing the pulse trains consists of motorized interferometers and enables precise control over the pulse train parameters like pulse spacing and amplitude. It is operated with a laser providing 400 fs pulses and energies of up to 110 mJ, which is the highest yet attempted for a pulse-train-type experiment. Opposed to earlier work, pulse division is done after amplification making the system more flexible in terms of tuning the pulse number. We present initial results of an experimental campaign of multicycle THz generation in custom periodically poled crystals with large apertures up to 10x20 mm². The available pump energy allows filling these apertures at high fluences, promising increased THz yields. We investigate the dependence of the conversion efficiency on the single pulse duration and aim to find the optimum pulse number for different crystal lengths to determine the efficiency limitations in a regime avoiding laser-induced damage. Since crystal length and pulse number define the bandwidth of the THz pulses, this work demonstrates a path to an optimized THz source tunable to different requirements of applications.

High-dimensional spatial entanglement of photons is versatile yet difficult to harness. We demonstrate an efficient direct measurement of the OAM spectrum of an SPDC source using the stimulated parametric down-conversion in the low-gain regime.

Orthogonal optical coding is widely used in classical multi-user communication networks. Using the phase conjugation property of stimulated parametric down-conversion, we extend the current time-domain orthogonal optical coding scheme to the spatial domain to encode and decode image information. In this process, the idler beam inherits the complex conjugate of the field information encoded in the seed beam. An encoding phase mask introduced onto the input seed beam blurs the image transferred to the idler. The original image is restored by passing the coded transferred image through a corrective phase mask placed in the momentum space of the idler beam. We expect that this scheme can also inspire new techniques in secure image transmission, aberration cancellation, and frequency conversion imaging.

Our presentation explores design strategies for high-flux High-Harmonic Generation (HHG) sources, using advanced nonlinear technologies like optical-parametric chirped-pulse amplifiers and multi-pass cells with Yb-doped lasers. Demonstrating immense power scalability and optimal HHG driver parameters, we present systems efficient at various wavelengths, promising significant applications in fields like material science and semiconductor metrology.

We study the frequency up- and down-conversion based on the cascaded process which accompanies large phase mismatching between fundamental and intermediate waves. So, for example, we propose using the cascaded Second-Harmonic Generation (SHG) to implement the frequency conversion process, which is similar to that occurring in a medium with cubic susceptibility. At phase matching between the fundamental wave and the third-harmonic wave, Third Harmonic Generation (THG) occurs with high efficiency (94.5%). We demonstrate that the cascaded process may also influence negatively on the frequency conversion processes. SHG in a medium with combined quadratic and cubic nonlinear response accounting for weak THG at large phase mismatching demonstrates that in some cases, the second harmonic intensity evolution is different, whether we take into account of weak THG process or not. So, then the intensity at doubled frequency may be much lower in certain sections in comparison with those without accounting for THG. We study such an influence of weak THG both for pulses with long duration by developing analytical approach and for short pulses based on computer simulation.