Solid State Lasers XXXIV: Technology and Devices

We present an erbium only 4-stage master oscillator power amplifier (MOPA) capable of reaching 200W average power at 20kHz repetition rate, operating at 1582nm. The MOPA can operate over a range of repetition rates ranging from 2kHz to 70kHz. At 2kHz, the MOPA produces 17.4mJ pulses. To our knowledge, this is the highest average power pulsed erbium only laser source. The system utilises two pre-amplifier stages, with a 30µm erbium doped fibre amplifier (EDFA) and a 50µm EDFA followed by a large core (100µm) EDFA used in the power amplifier. The power amplifier is co and counter pumped with maximum pumping power of 650W. The launched slope efficiency of the power amplifier is 33%. Amplified spontaneous emission at 1563nm is observed to be >30dB lower than signal power at 15mJ. The current limitations of this MOPA system are pump power and optical damage to the output fibre facet.

L3harris/ Kiger has been developing erbium/ytterbium (Er/Yb) co-doped phosphate laser glass for over 47 years. We have pioneered new laser materials and Q-switched eye safe-wavelength laser transmitters for range finding, illumination, tracking, and targeting. We have customized Er/Yb laser glass composites for developing mini-laser transmitters emitting 0.2-15mJ at 1.54um, with repetition rates from single shot to 100Hz over an operating temperature range from -40⁰C to 85⁰C with no active cooling.

Output power exceeding 200 W at an absorbed slope efficiency reaching 69 % has been achieved from a Tm-doped silica fibre laser. The laser produces an output beam that is the fundamental mode at a wavelength of 1.94 µm. A novel non-uniform Tm-doping profile is employed across an 8.2 µm diameter core to maximise the ‘two-for-one’ cross-relaxation while maintaining a reduced thermal loading density compared to a conventional uniform Tm-doping profile. The fibre is pedestal-free, allowing convenient, low-loss splicing to standard passive fibres. To our best knowledge, this is the highest continuous-wave output power in the two-micron band from a single-mode Tm-doped fibre laser with a small core-size diameter, non-LMA core, and non-pedestal design.

Demonstration of pulsed, tunable, Tm:Yap lasers is presented utilizing either an Acousto-Optic Modulator (AOM) or a Passive Q-Switch (PQS) crystal. Tunability is achieved by inserting etalons in the laser cavity. The AOM design achieved pulsed energies up to 2.3 mJ, 1926 - 1961 nm tunability range, 0.15 nm spectral bandwidth and pulse durations of 30nsec at 1 kHz. The PQS design demonstrate 1911 - 1952 nm tunability, maximal energy/ pulse of 1.42 mJ, 30ns pulse durations at 3 kHz. The combination of these features in the same cavity, makes them a promising tool for biomedical, sensing, and material processing applications.

Traditional laser gain materials for generation of near 2-µm output at high-average power include Tm:YLF and Tm:YAG. Both materials have high saturation energies, which makes efficient extraction of stored energy rather challenging. A recently introduced thulium sesquioxide (Tm:Lu2O3) is an emerging high-performance material, which overcomes the limitations of the traditional materials: it has a modest saturation fluence, more favorable spectroscopy, isotropy, superior thermal conductivity, This paper reports on the development and operation of the nanosecond-class ceramic Tm:Lu2O3 at high average power. Such lasers may be used for laser material processing, remote sensing, and laser acceleration of subatomic particles.

We report the development and thermal characterization of a Ho³⁺ doped germanate laser emitting at approximately 2.1 µm. Utilizing a simple Fabry-Pérot laser cavity (unoptimized), the laser demonstrates a slope efficiency of 20%, with a full width half maximum (FWHM) spectral width of 8 nm, and a peak output at 2095 nm. The laser setup, comprising a 4.8 mm long germanate gain medium sandwiched between input and output coupler mirrors, achieves a maximum output power of 32 mW at an absorbed pump power of 250 mW. Beyond the threshold of 250 mW absorbed power, a decline in laser output power was observed, indicating thermal effects within the cavity. A detailed thermal analysis was performed using the ABCD matrix approach, revealing a sensitivity factor for the thermal lens of 31 m-1W-1 and an optical path distortion length greater than + 6 μm. The findings suggest that thermal lensing significantly impacts the focal length and stability of the laser output. These insights are crucial for optimizing the performance and stability of Ho³⁺ doped germanate lasers for applications requiring shortwave to mid-infrared emissions.

We report on a compact 2.09 µm Ho:YAG thin-disk laser directly pumped with a 1.91 µm diode laser. High-peak-power operation in single-mode beam was achieved using the cavity-dumping technique, producing pulses with 6.2 mJ energy, 3.7 ns duration, 1.7 MW peak power, and 0.66% RMS pulse-to-pulse stability at 500 Hz repetition rate. Performance of the laser system in Q-switched and CW operation will be also presented. High peak power and brightness of the laser output makes it promising for various applications, such as 2-µm LIDT measurements or as a driving source for laser-induced breakdown spectroscopy.

In this presentation, we report on the characteristics of a narrow-linewidth, monolithic Ho:YAG nonplanar ring oscillator (NPRO) for use as a seed laser for a multi-stage Holmium based fiber amplifier. We achieve single-frequency operation with excellent beam quality, a high degree of linear polarization and a high power stability over a wide range of frequencies. Dependent on the used coating, we measured up to 50 mW output power at a wavelength of 2090 nm and up to 350 mW at 2122 nm.

For some medical and remote sensing applications, high average power and high pulse energy laser emission is required. In addition to higher output, improved beam quality is also desired. One method to achieve both a higher output and an improved beam quality is to combine the output of multiple resonators. We report on the output of a combined system with 4 independently operating Chromium, Thulium, Holmium doped YAG (CTH:YAG) or Ho:YAG resonators lasing on the 2.13 um transition. We have demonstrated an output of 200 W operating at 40 Hz using a novel method of interleaved beam combination where a rotating prism captures the beam from four separate resonators and translates them to a single optical path. With the stability of a compact package, the resonator described herein allows for a simple method of reaching higher average powers for a single wavelength or of a combination of different wavelengths along a single optical path. Potential applications include urology, dermatology, remote sensing, and as a pump source for other lasers.

This presentation explores the diverse applications of the microsecond pulsed 2.94μm Er:YAG laser. It can pump mid-wave infrared (MWIR) Fe:ZnSe lasers, enabling diffraction-limited, high average power outputs suitable for free-space propagation. Additionally, it can pump femtosecond MWIR Fe:ZnSe amplifier. In medicine, this laser offers precise bone cutting and drilling for spinal and skull procedures, potentially replacing traditional drills and saws. Industrially, it can cut and drill glass and semiconductors. Furthermore, its short absorption length in water holds promise for localized heating applications such as collapsing aqueous bubbles.

A time-dependent numerical laser model based on a quasi-three level system was developed to better understand and verify the experimental results of two different pulsed Alexandrite laser systems. The model incorporates temperature-dependent Alexandrite transitions and measured data to generate similar conditions as in the laboratory. Comparisons were made for the first time between simulated and experimental results in output energy, pulse duration, temporal shape, and laser wavelength. Moreover, the model was used to identify limiting experimental factors. We will present the outcomes of the numerical analysis and the excellent agreement with the experimental data of the pulsed Alexandrite laser.

We report on progress of the initial commissioning of the main high energy Ti:Sa amplifier in the EPAC facility; designed to produce petawatt pulses at an unprecedented 10 Hz repetition rate. During the first phase of operation, the amplifier will produce 30 J pulses pre-compressor, increased to 50 J pre-compressor in the second phase. The Ti:Sa amplifier uses a multi-slab design in a single amplifier head cooled by near-room temperature helium gas. A high-energy amplifier at this repetition rate is made possible by the pump laser; the frequency doubled output of a 100 J-class DiPOLE system providing 70 J pulses at 515 nm at 10 Hz. The amplifier is seeded by 4 ns, 1 J-level broadband (740 nm – 850 nm) pulses from an all-OPCPA front end. Broadband output from the Ti:Sa amplifier will enable pulse compression to 30 fs to deliver petawatt peak power pulses to the experimental areas.

A comprehensive simulation method for assessing optical depolarization effects in actively Q-switched solid-state lasers using Pockels cells is presented. Active Q-switching in these systems is achieved by modulating the beam polarization using a Pockel Cell, which induces the necessary losses for Q-switching. Additional depolarization losses within the laser crystal, primarily due to thermal effects from intense pumping, further impact the system’s performance and quality. The simulation framework employs finite element analysis (FEA) to conduct thermal and stress calculations, addressing the three-dimensional nature of depolarization within the crystal. Following this, a two-dimensional Jones matrix analysis is utilized to model the laser cavity, incorporating additional roundtrip losses arising from the crystal, polarizers, and/or retarders. The orientation of the crystal cut is also factored into the depolarization loss calculations to ensure accuracy. The numerical results provide insights into the critical factors influencing the performance and stability of high-powered active Q-switched lasers, ultimately contributing to improved laser performance and reliability.

Passively q-switched lasers utilizing Vanadium:YAG as the saturable absorber and operating at approximately a 1.3 micron wavelength offer a robust, unique and “eye safe” alternative to the 0.9 and 1.5 micron wavelengths utilized in LiDAR systems today. In addition to being more compact and less expensive than a 1.5 micron fiber laser, these lasers can be rapidly tuned in pulse repetition frequency with only small changes in pulse energy. A diffraction limited output combined with pulse energies in the 10 microjoule range allows high resolution and detection of small targets at ranges exceeding 1.5 km.

We experimentally demonstrated that thick cladding multimode optical fibers allow for almost 100% energy coupling efficiency, the highest damage threshold up to 30 mJ at 2 ns pulses even when bent to 150 mm radius. To the best of our knowledge, this is the highest energy density transmitted via a step-index fiber to date at such short laser pulse length, opening a way for reliable fiber-distributed, multiplexed laser ignition and decreasing the overall cost of any laser processing systems incorporating a laser whose energy is too high for one application spot.

For the purpose of engine ignition, we developed and numerically modelled a diode pumped Yb:YAG passively Q-switched laser oscillator operating without active cooling and delivering short bursts of nanosecond pulses. Unfortunately, the modelling results presented large discrepancies from experimental ones. We improved the model since, adding Nd:YAG lasers modelling capability, as Nd:YAG is less sensitive to thermal effects than Yb:YAG, and using a larger set of experimental results as a basis for comparison to find out where the discrepancies came from. Improvements made to the model after this study to better fit experimental results will be detailed.

Crystalline fibers based on Yb:YAG hold great promise for power scaling. High quality small core crystalline Yb:YAG fibers have been drawn by various groups; however, implementation in lasers is currently limited due to the lack of suitable claddings for these fibers. Researchers at Army Research Laboratory demonstrated the highest power for small core (~100 µm) cladded single crystal fiber (1% Yb:YAG fiber clad with undoped YAG) reaching 0.5 W average power (50 W peak power at 1% duty cycle), limited by thermal effects. In contrast to crystal clad fiber, glass cladding allows tailoring of the glass compositions to match numerical aperture’s of existing silica-based fiber laser components. We report on fabrication improvements of glass cladded single crystal Yb:YAG fiber. Laser characterization using a MOPA architecture was performed. We demonstrate 3.2 W output average power with 14.7 dB gain from a glass cladded 100 µm core Yb:YAG fiber.

This talk will focus on the growth of single crystal Lu2O3 fibers containing a wide range of Yb3+ ion doping. Thermal conductivity, Raman scattering, spectroscopic measurements and preliminary amplification studies will be presented. Single crystal cladding using hydrothermal growth of undoped Lu2O3 onto the core will be discussed.

This presentation will focus on the integration of advanced monitoring and control techniques in single-crystal fiber (SCF) growth, which have enabled improvements in precision, quality, and scalability. By integrating a custom two-wave pyrometer system, we have achieved high-resolution, non-contact temperature mapping of the melt zone, enabling visualization of melt dynamics during the growth process. This capability is fundamental for reducing defects, optimizing compositional control, and enhancing the uniformity of crystal growth. Additionally, machine vision tools provide high-resolution visual feedback of the melt zone, enabling automatic adjustments through the use of a custom melt model and advanced control strategies. These combined methods ensure consistent, sustained SCF growth. Together, these advancements form a reliable and scalable approach for producing high-quality SCFs.

Inter layer surface activated bonding between Cr3+-doped LiSrF6 (Cr:LiSAF) and sapphire crystal has been demonstrated. The bonding was realized between sapphire crystal and 1.5 at.% doped Cr:LiSAF with anti-reflexion (AR) coating to compensate the Fresnel losses due to large refractive index mismatch between the two materials (1.3 for Cr:LiSAF and 1.8 for sapphire). Thermal diffusivity measurements reveal that the bonding allows an improvement of a factor 3 for the composite material compared to bulk Cr:LiSAF. Based on these results, a bonded chip was designed to handle 20 W pumping for laser operations.

The increasing demand for ruggedized optical solutions in the midwave and long wave infrared spectral regions for airborne and space applications brings the challenge of ensuring proper qualification and reliability for complex component designs. Silver halide materials, known for their broadband infrared transmission, are photosensitive and can be altered by exposure to ionizing radiation. This paper outlines strategies to enhance the resilience of halide-based components, with transmission capabilities ranging from 0.5 microns to over 25 microns, against the effects of the space environment. The space qualification of these materials is examined for their use in sensing and optical communications.

Thulium lasers operating on the 3H4 → 3H5 transition offer a viable solution for addressing the spectral range around 2.3 µm being relevant for bio- and environmental sensing. Recently, upconversion pumping schemes of Tm ions relying on the resonant excited-state absorption have attracted a lot of attention. In the present work, we report on a Watt-level Tm:LiYF4 laser at 2.3 µm with upconversion pumping by a Raman-shifted 1.45-µm fiber laser. This laser delivered a record-high output power of 1.16 W with a slope efficiency of 40.8%, a laser threshold of 0.57 W, and a linear polarization (π). Evidence of the photon avalanche mechanism in populating the intermediate Tm-ion manifold (3F4) is provided by studying the power-dependent pump absorption efficiency. The polarized spectroscopic properties of Tm ions in LiYF4 are reported as well.

Laser finds a range of applications from the electronic sector, medical sector, and industrial sector, to applied science to high-end defence systems. This research paper has the goal of examining Solid State Laser from the point of view of materials, technologies and applications. The list of current applications is constantly updated thanks to the progress made by the rate of advancing research. This virtuous association is possible thanks to the continuous interconnection of current research processes with the developing market. In the future, the author will experiment with new applications and the emergence of new needs and new fundamental research fields, fostering the study of new materials, the development of new technologies and the progress of the existing field.

This paper introduces a high small-signal gain laser amplifier using a Yb:YAG crystal in triple-pass configuration, pumped at 969 nm for optimal absorption and reduced thermal effects. Our advanced simulation model, which includes a detailed analysis of amplified spontaneous emission (ASE), was validated against experimental data, showing excellent agreement. The results demonstrate that the triple-pass design significantly outperforms conventional single-pass configurations, offering substantial improvements in small-signal gain. This innovative amplifier design has promising applications in industrial, scientific, and medical fields, providing a framework for future advancements in high-performance laser technology by optimizing performance and minimizing the signals ASE content.

Diamond Raman lasers (DRLs) have in recent years been investigated as a possible laser source that features high output power, single frequency spectra, and large wavelength flexibility, ranging from UV-NIR inclusive. Recently we reported significant linewidth narrowing of >104 relative to the input pump linewidth (resolution limited), which was attributed to the phonon-damping effect in the three-wave Raman interaction. Here we report a combined model and experimental investigation into the linewidth compression in Raman lasers, where we adapt the equations for the tree-wave interaction to show that much higher compression factors are predicted due to the short Raman T2 time with linewidth compression factors of >108 achievable. We present experimental measurements of the linewidth for a DRL operating at 589 nm. Using these results, we propose pathways to attain sub-hertz linewidth DRLs, with 10s of watts of output power, and wavelength flexibility across the UV-NIR spectrums.

A concept to efficiently transfer energetic near-nanosecond pulses to the sub-picosecond scale is proposed: Pre-shaped pulses are sent into multi-mirror multi-pass cells which enable km-scale nonlinear propagation. In this way, the initial pulse bandwidth can be extended by more than three orders of magnitude. To verify the concept, spectral broadening of 100-mJ, 300-ps pulses to a sub-300 fs transform-limit in a 1-m diameter multi-pass cell was simulated. Moreover, an 11-mirror cell was set-up and 300 MW peak power pulses were spectrally broadened in air over 297 passes. The experiments showed that excellent beam quality and high-power transmission can be obtained in the investigated multi-mirror arrangements. The concept presents a new gateway for industrial mature, high-power lasers to the ultrafast regime and is, for instance, attractive for high repetition rate laser-particle acceleration applications.

High optical efficiency with excellent beam quality has been demonstrated in a 946-nm Nd:YAG laser and a 1592-nm Er:YLF laser, as enabled by cryogenic cooling of the laser gain elements to 80 K. Continuous-wave operation to over 90 W at 946 nm was attained with 70% slope efficiency. The beam quality was M2 ~1.1. The Er:YLF laser was longitudinally pumped at 1544 nm with an Er-doped fiber amplifier. Up to 10 W cw output at 1592 nm was attained with a slope efficiency of 79%. The polarization was linear, and the output was TEM00 mode.

We are discussing the recent progress in cryogenically cooled Yb:YLF lasers for high average power and high pulse energy lasers. Detailed spectroscopic measurements of Yb:YLF at cryogenic temperatures are performed and in-situ laser parameter diagnostics is introduced. Based on the measured laser parameters a detailed laser model is developed that enables the development of efficient cryogenic laser amplifiers. A seed laser providing watt level average power with broadband pulses (~12 nm) at 1015 nm is developed and used to exploit the full bandwidth of Yb:YLF. We report results from our line of laser amplifiers, including regenerative and multi-pass amplifiers that extract hundreds of watts and high-energy pulses with hundreds of millijoule pulse energy and subpicosecond pulse duration, marking a significant step forward in the field. Further development steps in Yb:YLF technology are proposed eventually opening the path to joule level pulses and even shorter pulse durations eventually overcoming current limits to ytterbium lasers.

Circular pump architecture can well improve uniformity of side-pumped laser amplifier. With this kind of architecture, the amplifier we designed has maximum stored energy above 5 J, and the P-V value 2.8% over the 15-mm full diameter at the optimized working current region. When a samarium-doped ASE-absorptive flow tube was used to instead the conventional glass flow tube, the gain ability of the circular-pump-architecture laser amplifier can be improved from 7.7 to 13.5, 1.75-fold with the maximum working current. Fluorescence measurement results shows that replacing the conventional flow tube with the ASE-absorptive flow tube can increase the inverse population number by approximately 30% in the peak working current regime of 200~250 A. Neglecting nonlinear and saturation effects, fitting the linear curve yielded a slope for the data obtained using the ASE-absorptive flow tube that was 1.32 times that obtained using the conventional flow tube.

We report a compact and packaged ~1557 nm planar waveguide free-running frequency comb chip laser. The gain medium is erbium doped fluorozirconate glass waveguide chips that emit ~ 6 nm wide (FWMH) combs with P=10 mW when the cavity is configured for a 1 GHz repetition rate. The comb includes piezo cavity length control, an ability to tune the repetition rate by up to 10 MHz, and the output is via polarisation maintaining fibre. The presentation will cover phase noise, relative intensity noise, comb line stability, and pulse width measurements.

This laser emits a central wavelength of 2 µm and boasts impressive capabilities: pulse energies exceeding 100 µJ and an average power output surpassing 15 W at less than 400fs pulse duration. Designed for longevity, it is tailored for industrial applications, seamlessly integrating into laser machines used for materials processing. The laser’s parameters are particularly well-suited for working with semiconductors like silicon. It enables essential tasks such as microwelding or precision cutting of filaments.

Regenerative amplifiers based on Titanium Sapphire have made a significant contribution to many areas of both scientific and industrial applications. These laser systems are capable of generating mJ-level pulse energies with sub-100 fs pulse durations. In this talk, several product enhancements are discussed including a reliable means for producing <25 fs pulses, a robust scheme for achieving long-term carrier envelope phase-stabilization and key mechanical enhancements focused on increased reliability will be discussed.

Ultrafast lasers are expanding beyond traditional micromachining and medical applications, now providing solutions for telecommunications, aerospace, and microwave photonics through enhanced ruggedization. Menhir Photonics has developed solid-state 1.5 µm ultrafast lasers with unprecedented robustness, featuring the lowest phase noise and timing jitter on the market. Achieving a groundbreaking 10 GHz fundamental pulse repetition rate, an unmatched milestone for passively modelocked femtosecond solid-state lasers at 1.5 µm. These compact and ruggedized lasers advance towards flight and space compatibility. The latest 10 GHz MENHIR-1550 development, the first commercial product of its kind, will be showcased, along with applications such as ultra-low noise microwave generation, ultra-fast quantum-limited dual-comb spectroscopy, highly secured telecommunications, and photonics analog-to-digital conversion.

Ytterbium (Yb) 1030 nm femtosecond lasers have already secured their ground in both scientific and industrial areas. Thanks to their high average power and high repetition rate coupled with industrial-grade stability, Yb lasers have strengthened and expanded the variety of applications, such as ultrafast spectroscopy [1]. However, up to now, there has been a certain parameter space that seemed to be reserved for Ti:Sapphire (Ti:Sa) amplifiers. In this talk, we will cover the most recent results of amplifying Yb lasers to multi-mJ-level pulse energies.

We have developed a highly reliable deep-UV 266 nm picosecond laser source with an average power of 6 W by using β-BaB2O4 (BBO) crystal. The collimated output beam had a beam quality factor (M2) of ~1.2 and a beam circularity of over 90%. Stable continuous operation of over 250 hours at 6 W output power was demonstrated with no significant degradation of beam quality and efficiency.

A 7J, 527nm laser with 4ns pulse width with a square temporal profile at 10Hz has been demonstrated. The design and results will be reported.

Cryogenic cooling of quadratic nonlinear crystals is studied and demonstrated at low-power as a mean to remove thermal bottlenecks for average power scaling of various optical frequency-conversion stages, thanks to the combined improvements of thermal parameters and phase-matching temperature tolerance. This technique has been used in solid-state laser amplifiers like titanium-sapphire for two decades but never in nonlinear optical crystals, where it offers similar advantages regarding thermo-mechanical parameters. We report here on the existence of crystal cuts with much enhanced phase-matching tolerances in the ubiquitous lithium triborate crystal for common processes like type I and type II second-harmonic generation at 1064 nm, type I and type II sum-frequency mixing to 355 nm and type I sum-frequency to 266 nm. Thermo-mechanical and thermo-optical analyses indicate that cryogenic cooling is even more favorable than for laser amplifiers. Simulations show that it could overcome all average-power limitations in a foreseeable future. It would make it possible to efficiently convert the highest average-power thin-disc or fiber lasers available today in the multi-kW range and above.

Frequency-converted lasers are used in wide range of industrial applications. A good example for a large volume 24/7 application is the processing of display components in the consumer electronics industry [1-3]. These applications require robust industrial laser sources with high availability as well as demanding performance parameters to achieve high productivity. Besides the progress in the well-known parameter range, we will present our latest results on very high laser powers in the green, several hundred’s of Watts in the UV, and tens of Watts in the DUV for new and emerging applications in the consumer electronics industry and e-mobility featuring state-of-the-art laser lifetimes.

We realized the first 0.5 mm thin all solid-state single frequency ruby disc laser. Due to the short cavity the ruby laser emits a single longitudinal mode with an output power of 15 mW when pumping with one laser diode. However, the power can be upscaled when using more pump lasers

This paper reports on the development of a picosecond laser system delivering an output at near 1 micron wavelength, which is used to drive an optical parametric amplifier (OPA) seeded by a supercontinuum laser. The OPA output can be wavelength-tuned over of broad portion of the visible spectrum. The resulting wavelength-tunable system will be used as a photocathode driver in high-brightness electron beam accelerators.

Since the groundbreaking achievement of ignition and self-sustaining fuel burn at the U.S. National Ignition Facility (NIF), the field of fusion, specifically laser inertial fusion energy (IFE), has rapidly accelerated and transformed. Numerous countries are investing more heavily or initiating new fusion programs, with significant collaborative efforts from international research institutions and the private sector accelerating the path to practical fusion energy. The implications for the photonics market include an increased demand for lasers, optics, optical materials, diagnostics, and other key technologies, creating new opportunities for photonics companies and shifting market dynamics. Future challenges and strategies for achieving higher energy yields and commercial viability are outlined, emphasizing the critical role of photonics in enabling the next generation of fusion energy solutions.

The interaction of light and matter can create bonding structural and morphological changes in nano/micro-scale from the surfaces of diverse materials, sometimes even deep within them. This feature has been utilized in laser processing to produce new value for both science and industry. Recent advances in high-power, ultrashort pulsed laser and fast beam delivery technologies are rapidly expanding the possibilities of laser processing. At the same time, the number of parameters to be controlled has become enormous, which is why we have introduced Data Science. In this talk, we will discuss new data-driven laser processing utilizing high-speed data acquisition and AI data optimization for higher throughput and quality. We also aim for this technology to contribute to sustainable manufacturing and society in the future.

Optical frequency combs have revolutionized time and frequency metrology by providing rulers in frequency space that measure large optical frequency differences and/or straightforwardly link microwave and optical frequencies. One of the most successful uses of frequency combs beyond their original purpose has been dual-comb interferometry. An interferometer can be formed using two frequency combs of slightly different line spacing. Dual-comb interferometers without moving parts have no geometric limitations to resolution, therefore miniaturized devices using integrated optics can be envisioned. Dual-comb interferometers outperform state-of-the-art devices in an increasing number of fields including spectroscopy and holography, offering unique features such as direct frequency measurements, accuracy, precision, and speed.

Today, approximately 12,000 satellites orbit Earth. By 2030, estimates show numbers above 60,000. Today, we service spacecraft when absolutely necessary. By 2030’s, in-space services will be routine; refueling, repair, relocation, assembly, and manufacturing. Advances are underway to realizing this future, enabling a sustainable version will require photonics technologies.

We report the first red diode-pumped femtosecond alexandrite laser with suffi-ciently high pulse energy for various applications, including multiphoton imaging. We developed a SESAM-modelocked oscillator with chirped mirror dispersion compensation, generating near transform-limited pulses with 97 fs duration and a pulse energy of 3.8 nJ at 84 MHz pulse repetition rate. The laser emitted at 747 nm with a spectral width of 6.1 nm FWHM and excellent beam quality (M2<1.1). An average power of 315 mW was achieved using 1% output-coupling and 5.3 W of pump power from a fiber-coupled diode laser module with 105 µm core diameter and 0.22 numerical aperture emitting at 635 nm. The RF spectrum analysis confirmed stable modelocking with 72 dB signal-to-noise ratio.

We present experimental results on a multi-axial mode seed used to efficiently achieve high power frequency doubling in the green spectral region via external resonant doubling. Tens of axial modes with an individual linewidth below 10 kHz were generated using a Nd:YVO_4 laser. After an amplification stage, an external cavity resonator was implemented to achieve tens of Watts of output power at 532 nm using an LBO non-linear crystal. The proposed design provides new insights on SHG power scalability of such sources.

We present results of ultra-compact (around 1cm3) diode-pumped solid-state microchip lasers operating at the kW-level of output peak power for high-efficiency second-harmonic-generation in the UV and visible wavelength range. We demonstrate 69% conversion efficiency at 532nm using periodically poled lithium niobate using a 2.9kW 1064nm laser. Further results at other UV and visible wavelengths are also presented.

This study numerically performs the thermally induced refractive index distribution in a YAG/Yb:YAG/Cr:YAG laser medium to analyze interference patterns between two synchronized Q-switched pulses in a longitudinally pumped single laser resonator with a 1x2 pump beam array. The close spacing of pump beams is crucial for synchronization. The off-axis entry of each pump beam into the gain medium induces an asymmetric refractive index and altering the medium's shape. The temperature distribution is calculated using absorption characteristics, revealing the correlation between thermal refractive index changes and the measured interference patterns. The study also examines the output polarization characteristics influenced by the asymmetric refractive index.

This study aims to explore the operational boundaries of Erbium-Ytterbium co-doped glass over a broad temperature spectrum ranging from -20°C to +60°C, and to explore resonator designs that minimize the impact of constraining factors such as the material's low thermal conductivity and pronounced thermal lensing effects. Modifications to the resonator design were implemented through thermal modeling and experimental validation to mitigate these limitations. Furthermore, a comparative case study was conducted on passively Q-switched, diode-pumped solid-state (DPSS) lasers, examining their performance in both single-pulse and burst firing modes.

We have demonstrated through simulation a few Watts, tunable wavelength, visible laser system. We used gain-managed nonlinear fiber amplifier output as the broadband seed pulse as opposed to the standard white light generation. The advantages of gain-managed nonlinear seed pulse compared to conventional methods are uniform and high spectral energy density. Furthermore, the inherent quasi-linear chirp of the proposed seed pulse is the key factor in tuning the output wavelength from 500nm to 600nm arbitrarily. Our tunable laser has potential use in high-demand applications such as spectroscopy, imaging as well as free electron laser facilities.

We report on comparative study of efficient diode-pumped CW Nd:YVO4 and Nd:GdVO4 lasers pumped at 914 nm and 912 nm, respectively. A fiber-coupled laser diode with 105 μm core diameter, numerical aperture of 0.22, and maximum output power of 60 W was implemented as a high power optical pump source to excite Nd:GdVO4 and Nd:YVO4 gain media. Both crystals were 20 mm-long (a-cut with 1.5 at. % doping) and were used in a three-mirror cavity. The maximum average output power of the CW Nd:YVO4 laser was measured to be ~20.2 W at 39.4 W of the absorbed pump power. This corresponds to the optical efficiency and the slope efficiency of 51.3% and 56.7%, respectively. The CW Nd:GdVO4 laser achieved the maximum output power of 17.9 W at 38.04 W of the absorbed pump power. This corresponds to the optical efficiency of 47% and the slope efficiency of 52%. The measured beam quality factors of the lasers were approximately 1.1 for the Nd:GdVO4 and 1.2 for the Nd:YVO4. The observed output beams displayed TEM00 transverse Gaussian intensity profiles. Thermal lensing properties were also compared.

High-resolution long wavelength (>880 nm) absorption spectra of common laser gain media were recorded to identify the longest possible pumping wavelengths. This is needed to reduce the quantum defects and to minimize the heat generation in the gain media. According to the results of measurements 912 nm and 914 nm were identified as the appropriate pumping wavelengths in Nd:GdVO4 and Nd:YVO4 gain media, respectively. To pump the Nd:YAG and Nd:YLF crystals with low quantum defects, one can implement laser diodes emitting at 938/946 nm and 908 nm, respectively. High-resolution absorption spectra of other gain media were also recorded.

The KLTN crystal, is a promising candidate for EO modulation at long wavelengths up to 5.5 µm. KLTN at the para-electric phase manifests a quadratic EO effect which upon approaching the ferroelectric phase transition, becomes remarkably large, exhibiting an electrically induced change in the refractive index of approximately 0.01 while maintaining high optical quality. Recently, we developed actively Q switched laser at the 2µm range implementing polarization modulation with KLTN crystal. Here we present new configuration of actively Q-switched Tm:YLF laser based on a quadratic electro-optical KLTN deflector. Deflection was achieved due to the electro-optical effect gradient along the vertical axis, which was caused by inducing an electric field gradient along the vertical axis due to the trapezoid shape. Maximal high energies/pulse of 4.2- 6.9mJ were achieved in three repetition rates of 0.4, 0.5 and 0.7 kHz with a relativity low applying voltage of 500V and with 15ns pulse duration range.

We present a comparative study of the wavefront stability of joule-class, 1053-nm Nd:YLF ring amplifiers with flashlamp and diode pumping operated at 5 Hz. The pump timing with respect to the seed pulse was varied to study the pumping effect with and without laser amplification. When using flashlamp pumping and no laser amplification, we observed strong shot-to-shot wavefront fluctuation after four round trips, which is attributed primarily to the increased air turbulence induced by the large amount of heat released from pumping. In contrast, diode pumping significantly reduced the root-mean-square (RMS) wavefront fluctuation by >4× to ~0.01 waves, which is comparable to the seed wavefront stability. The laser amplification slightly increased the wavefront instability by <1.5× in both cases. Diode pumping also reduced the RMS energy fluctuation from ~2% to <1%. The improved wavefront and energy stabilities allow high-energy Nd:YLF lasers to pump high-quality optical parametric chirped-pulse–amplification systems.

Optics and photonics are transforming rapidly as machine learning (ML) techniques advance in the field. These ML advancements require extensive datasets, often challenging to obtain experimentally. We present a start-to-end (S2E) software framework for high-power laser systems. Using this framework, we develop a digital twin for a complex laser system, including pulse shaping, amplification, and upconversion. We explore amplifier parameters to mimic experimental conditions and generate an ML model that achieves a 250-fold speed-up over traditional numerical simulations, paving the way for generalized digital twins and enhanced synergy between simulation and experiment.

An ytterbium-doped thin disk multi-pass amplifier is used for amplifying the output from two high power ytterbium-doped fiber amplifiers (YDFA). Two beams from two YDFAs were combined by the polarization. The powers of the YDFAs were both 2 kW and the combination power was over 3.6 kW. The emission centers from the ytterbium-doped YAG and YDFA are both around 1030 nm. The emission bandwidth from YDFA is more than 40 nanometers. On the other hand, the emission bandwidth of the Yb: YAG is only few nanometers. It is important to control the wavelength from the YDFA with high efficiency. A distributed feedback laser (DFB) was used for the seed of the YDFAs. The DFB laser wavelength was optimized for increasing the output power. The maximum output power was 4.6 kW when the seed wavelength was 1031.5 nm.

We demonstrate Kerr-lens mode-locked operation of an Yb:Ca(Gd,Y)AlO4 laser pumped with a 976-nm single transverse-mode, fiber-coupled laser diode. Soliton pulses as short as 25 fs are generated at 1080 nm via soft-aperture Kerr-lens mode-locking, with an average output power of 47 mW at ~65.6 MHz. To the best of our knowledge, this result represents the first demonstration of a diode-pumped Kerr-lens mode-locked laser based on an Yb:Ca(Gd,Y)AlO4 crystal exhibiting both structural and compositional disorder.

We are developing a hybrid ArF laser, consisting of solid-state laser oscillator and ArF amplifier, for laser material processing at 193-nm. To find the optimum configurations of laser processing for various materials, a pulse shape controlling system is required for the hybrid ArF laser. We have developed an Er fiber laser and an optical parametric amplifier in the solid-state laser oscillator which can change the pulse width from 5-ns to 20-ns with 1-ns resolution, also can generate the 0.5-ns burst pulse with the temporal separation of 3-ns.

We demonstrate Kerr-lens mode-locked operation of a Tm,Ho:Ca(Gd,Y)AlO4 laser pumped with a narrow-bandwidth, continuous-wave Ti:sapphire laser at 797 nm. Soliton pulses as short as 145 fs are generated at 2087.9 nm in -polarization via soft-aperture Kerr-lens mode-locking, with an average output power of 203 mW (0.2% output coupler) at ~80.5 MHz. To the best of our knowledge, this result represents the first demonstration of a Kerr-lens mode-locked laser based on a Tm,Ho:Ca(Gd,Y)AlO4 crystal exhibiting both structural and compositional disorder.

Sub-nanosecond mid-IR lasers are essential for applications like optical parametric amplification and material processing, yet effective sources are limited. This study explores room temperature Fe lasers at 4.4 µm, focusing on spike-like oscillation dynamics to generate sub-ns pulses from 40-60 ns Q-switched Cr:Er:YSGG pump pulses. By optimizing cavity length, gain element length, and output coupler reflectivity, we achieved significant pulse compression of over a factor of 50. Our simulations predicted an output energy of 1.7 mJ using a 17 mJ pump pulse. Experimentally, a single-spike oscillation yielded 0.39 mJ with 6.67 mJ pump energy was realized. These findings demonstrate the potential of Fe lasers for high-energy, ultra-short pulse generation in the mid-infrared range.

We developed a compact high peak power, nanosecond laser transmitter. The linear cavity laser considers a concave and a plane mirror, a Yb:Er:glass as the active medium, and an acousto-optic modulator (AOM) as the actively Q-switch. Our laser operates at peak power > 1 MW and pulse width < 10 ns. The repetition rate can be tuned from 1Hz to 20 Hz. The laser beam divergence is 4.5 mrad without collimating system. This laser is used in our laser rangefinder device with the range performance up to 40 km.

Broadly tunable continuous-wave Yb:KGW laser pumped by a compact Nd:YAG laser operating at 946 nm is reported. The intracavity SF10 prism was used for wavelength selection in a three-mirror-cavity setup. The range of wavelength tunability was found to be up to 106 nm with the maximum output power of >2.5 W at 1044 nm. In addition, a frequency-doubled configuration was also tested producing the blue-green radiation.

Lasers operating in the middle infrared region are useful for various applications ranging from free-space communication to biological tissue characterization. Transition metal-doped II-VI compounds, particularly Cr and Fe, are key materials for mid-IR lasers operating in the 2-5 μm range. However, producing high-quality transition metal-doped ZnSe crystals is challenging due to limitations in conventional doping methods. This study investigates the fabrication of transparent ZnSe ceramics using spark-plasma sintering (SPS). The "green body" was fabricated by grinding polycrystalline CVD ZnSe into sub-micron powders. Sintering was performed at pressures up to 90 MPa, and temperatures up to 1200 °C under a vacuum with argon gas purging. The resulting ceramics achieved 99.9% density relative to single crystals. Additionally, the effects of adding binders (LiF) and hot isostatic pressing (HIP) treatment was studied. Successful fabrication of transparent ZnSe ceramics demonstrates the viability of SPS as a method for producing TM-doped ceramics mid-IR gain media.

Tm:YAP crystals are ideal for 2μm lasers due to their wide absorption coefficient (~793nm), large wavelength tunability (1900-1960nm), and high quantum efficiency (~1.8) via cross-relaxation. However, strong thermal lensing complicates high-energy use. To better understand this effect, we developed a novel measurement method using the laser beam itself. By constructing a laser cavity with dual exit mirrors, we measured beam quality (M^2) and divergence to determine the focal length induced by thermal effects. Our findings show laser efficiency significantly impacts thermal lensing due to varying heat absorption, allowing us to recalculate the fractional thermal loading relative to laser efficiency.

CRYTUR company is developing and manufacturing series of doped large monocrystalline yttrium aluminum garnets (YAG), widely used as diode-pumped solid-state lasers active material. CRYTUR has recently introduced new thin-disk laser products that are results of the R&D collaboration between CRYTUR and HiLASE center. Yb:YAG thin-disk module, the high-power solid-state laser active medium, has been fully tested up to 1 kW laser pump power in the FM and MM operation exceeding 300W average output power in the MM. Further, the thin-disks from the Ho:YAG material providing 15W CW output have been developed, tested, and manufactured for the 2100 nm thin-disk laser setup for optical free-space communication purposes. For pumping of the Yb:YAG thin-disks the new compact thin-disk pump module, the thin-disk laser head, has been introduced also. The laser head has been tested with pump power up to 1kW for lasing in CW mode.

We report on the development of a compact method of beam combination using a rotating rhomboid prism. The prism is mounted on a motorized rotational stage and sequentially directs the output from multiple parallel resonators into a single beam. Rhomboid prisms are inherently insensitive to misalignment, so the entire system is very compact, stable, and simple to align. The first several iterations were used for combining four Ho:YAG resonators resulting in a system with a 2.13 um output of over 200 watts at 40 Hz. Although the methodology was initially demonstrated with Ho:YAG resonators, it is flexible and may be used for combining different types of lasers including multiple wavelengths.

Many medical, industrial, and military applications require high pulse repetition rate and high average power lasing devices. To produce higher repetition rates and/or higher average power systems, laser engineers often combine the outputs of multiple resonators using multiple laser drivers accordingly. MegaWatt Lasers has developed a Compact Multiple Pump Chamber Module that includes four high power pulsed flashlamps, each requiring individual pulse timing. Previously MegaWatt Lasers used COTS drivers for this application. The new multiple laser driver significantly reduces cost, size, weight, and complexity as well as improves signal timing. A single AC power circuit, HV DC power circuit, safety interlock circuit, microcontroller, diagnostic circuit and energy storage circuit are shared among multiple laser driver outputs, eliminating redundancy. The method of using a single high power HV charging module allows for reduced size and weight. The method also reduces component count – improving reliability and dependability. The method of using shared, integrated components improves timing accuracy as external cabling and discrete interface hardware are eliminated.

In solid state laser lasers, the gain media absorbs pump energy volumetrically. In the form of a rod, the gain media’s refractive index has a quadratic variation with radius. The first order effect is spherical lensing. Concave rod ends are commonly used to compensate for thermal lensing. In a simple resonator comprised of a bi-concave rod and flat mirrors, the resonator is stable when operated above the compensation average pump power and unstable when operated below. The resonator will perform better at higher average pump power and will perform poorly or not at all at lower average pump power. With the use of “Phantom” pulses, we have been able to extend operation of resonators with a bi-concave laser rod to low repetition rates. Phantom pulses are low energy, high repetition rate pulses used to thermally load the laser rod. The energy is below the lasing threshold and the repetition rate is low enough so that there is minimal stored energy left in the gain media when the main pulse occurs. By utilizing the phantom pulse technique, we were able to improve the resonator stability. This resulted in an increase in output energy and power of a CTH:YAG resonator by a factor > 3.

A novel high power 786nm VCSEL pumped Tm:YAG laser was demonstrated in this paper. A side-pumping chamber with 60 VCSEL chips and a 3mm diameter Tm:YAG rod was designed and pumping experiment was performed. Peak power of 750W at 2013nm was reached with pumping power of around 3888W at 786.1nm in 5ms pulse width at 10Hz with a coolant temperature of 10°C . The maximum optical-to-optical efficiency was calculated up to 20.3%. With features of low wavelength shift and high reliability in pulsed mode from the VCSEL, this Tm:YAG laser can be a potential alternative solution compared with conventional flash lamp or laser bar pumped Tm:YAG lasers for various medical applications such as urology and dermatology.

Few-cycle mid-wave infrared pulses were generated by passing a beam from a cryogenically cooled Fe:ZnSe chirped pulse amplifier at a repetition rate of 400 Hz through a gas-filled hollow core fiber followed by dispersion compensating bulk calcium fluoride. The krypton-filled fiber at 370 kPa yielded 1.14-mJ, 42-fs pulses centered at 4.07-µm, while the oxygen-filled fiber at 310 kPa delivered 0.78-mJ, 39-fs pulses spanning 3 to 5.5 µm. This work is a step toward a high repetition rate mid-wave infrared driver of isolated attosecond keV X-ray pulses.