High-power Yb Research Articles

High power and excellent beam quality rod Yb: YAG regenerative amplifier

High power and excellent beam quality rod Yb: YAG regenerative amplifier

Sub-Nanosecond, High Peak Power Yb:YAG/Cr4+:YAG/YVO4 Passively Q-Switched Raman Microchip Laser with the Emission of Multiple Pulses

This paper demonstrates the capability of sub-nanosecond, high peak power Yb:YAG/Cr4+:YAG/YVO4 passively Q-switched Raman microchip lasers at 1134 nm operated in multiple pulses mode under quasi-continuous-wave (QCW) pumping. Total pulse energy for the Stokes laser was 1.8 mJ with a 4 mm YVO4 crystal and TOC = 16%. The corresponding pulse repetition rate reached 225 kHz within a single pumping pulse. By employing a compact plane-concave cavity and 5 mm YVO4 crystal, the single pulse energy for the Raman laser was further scaled up to 44 μJ. The corresponding peak power was 95 kW. A highest output pulse repetition rate of 87.8 kHz and shortest pulse duration of 464 ps were found for the Raman laser. The results indicate that the Raman microchip laser configuration under QCW LD pumping is a promising approach for developing high peak power, commercial and portable Raman lasers with a pulse duration of several hundred-picoseconds at a pulse repetition rate of hundred kilohertz.

High-power sub-picosecond filamentation at 1.03 µ m with high repetition rates between 10 and 100 kHz

Filamentation has extensively been explored and is well understood at repetition rates <1 kHz due to the typical availability of multi-mJ laser systems at a moderate average power. The advent of high-power Yb-lasers opened new possibilities for filamentation research. However, so far, high average power Yb systems have mostly been explored to increase the driving pulse energy to several hundreds of mJ and not at significantly higher repetition rates. In this paper, we study, for the first time, long filaments at unprecedented high repetition rates of 10, 40, and 100 kHz using a 500-W Yb-doped thin-disk amplifier driver operating with sub-700 fs pulses. We compare the filament length, density hole, and fluorescence at a constant peak power but different repetition rates and find a strong dependence on filament length and density depletion with repetition rate. Our analysis reveals the emergence of a significant stationary density depletion at repetition rates of 40 and 100 kHz. The corresponding reduction in the breakdown threshold by increasing the laser repetition rate observed in our study signifies a promising avenue for enhancing the efficiency and reliability of electric discharge triggering in various scenarios. Using capacitive plasma probe measurements, we address the limitations of fluorescence imaging-based measurements and demonstrate a systematic underestimation of filament length. This work contributes to a deeper understanding of the interplay between laser repetition rates, filamentation, and heat-driven density depletion effects from high-repetition-rate high-power laser systems and will contribute to guiding future research, making use of filaments at high repetition rates.

Injection-seeded high-power Yb:YAG thin-disk laser stabilized by the Pound-Drever-Hall method.

We demonstrate an injection-seeded thin-disk Yb:YAG laser at 1030 nm, stabilized by the Pound-Drever-Hall (PDH) method. We modified the PDH scheme to obtain an error signal free from Trojan locking points, which allowed robust re-locking of the laser and reliable long-term operation. The single-frequency pulses have 50 mJ energy (limited to avoid laser-induced damage) with a beam quality of M2 < 1.1 and an adjustable length of 55-110 ns. Heterodyne measurements confirmed a spectral linewidth of 3.7 MHz. The short pulse build-up time (850 ns) makes this laser suitable for laser spectroscopy of muonic hydrogen, pursued by the CREMA collaboration.

Time-, spin-, and angle-resolved photoemission spectroscopy with a 1-MHz 10.7-eV pulse laser.

We describe a setup of time-, spin-, and angle-resolved photoemission spectroscopy (tr-SARPES) employing a 10.7 eV (λ = 115.6nm) pulse laser at a 1MHz repetition rate as a probe photon source. This equipment effectively combines the technologies of a high-power Yb:fiber laser, ultraviolet-driven harmonic generation in Xe gas, and a SARPES apparatus equipped with very-low-energy-electron-diffraction spin detectors. A high repetition rate (1MHz) of the probe laser allows experiments with the photoemission space-charge effects significantly reduced, despite a high flux of 1013 photons/s on the sample. The relatively high photon energy (10.7eV) also brings the capability of observing a wide momentum range that covers the entire Brillouin zone of many materials while ensuring high momentum resolution. The experimental setup overcomes the low efficiency of spin-resolved measurements, which gets even more severe for the pump-probed unoccupied states, and affords the opportunity to investigate ultrafast electron and spin dynamics of modern quantum materials with energy and time resolutions of 25meV and 360fs, respectively.

High Power (~10 kW) Yb:YAG Ceramic Slab Laser Operating at 1030 nm

A high power quasi-continuous-wave (QCW) efficiently-cooled ceramic slab laser oscillator is reported. The maximum output power can reach 9.85 kW with the optical-to-optical efficiency of 60% with respect to the absorbed pump power as well as the slope efficiency up to 65.3%. To the best of our knowledge, this is the highest output power for any Yb:YAG ceramic laser oscillator. Beam aberration of the efficiently-cooled Yb:YAG ceramic slab laser is detected by a parallel probe beam along the optical path of laser beam. The peak-to-valley (PV) value of the wavefront distortion is 2.8 μm under full output power. The beam quality factor β is estimated to be about 3.7 times diffraction limit while without additional correction system. A numerical model of temperature field is constructed to analyze the wavefront distortion of the probe beam, and the calculated results are in agreement with the experimental data.

Simple, stable and efficient nonlinear pulse compression through cascaded filamentation in air

Abstract Nonlinear compression has become an obligatory technique along with the development of ultrafast lasers in generating ultrashort pulses with narrow pulse widths and high peak power. In particular, techniques of nonlinear compression have experienced a rapid progress as ytterbium (Yb)-doped lasers with pulse widths in the range from hundreds of femtoseconds to a few picoseconds have become mainstream laser tools for both scientific and industrial applications. Here, we report a simple and stable nonlinear pulse compression technique with high efficiency through cascaded filamentation in air followed by dispersion compensation. Pulses at a center wavelength of 1040 nm with millijoule pulse energy and 160 fs pulse width from a high-power Yb:CaAlGdO4 regenerative amplifier are compressed to 32 fs, with only 2.4% loss from the filamentation process. The compressed pulse has a stable output power with a root-mean-square variation of 0.2% over 1 hour.

Spectrally tunable high-power Yb:fiber chirped-pulse amplifier

Tailoring the properties of the driving laser to the need of applications often requires compromises among laser stability, high peak and average power levels, pulse duration, and spectral bandwidth. For instance, spectroscopy with optical frequency combs in the extreme/visible ultraviolet spectral region requires a high peak power of the near-IR driving laser, and therefore high average power, pulse duration of a few tens of fs, and maximal available spectral bandwidth. Contrarily, the parametric conversion efficiency is higher for pulses with a duration in the 100-fs range due to temporal walk-off and coating limitations. Here we suggest an approach to adjust the spectral characteristics of high-power chirped-pulse amplification (CPA) to the requirements of different nonlinear frequency converters while preserving the low-phase-noise (PN) properties of the system. To achieve spectral tunability, we installed a mechanical spectral shaper in a free-space section of the stretcher of an in-house-developed ytterbium-fiber-based CPA system. The CPA system delivers 100 W of average power at a repetition rate of 132.4 MHz. While gaining control over the spectral properties, we preserve the relative-intensity-noise and PN properties of the system. The high-power CPA can easily be adjusted to deliver either a spectrum ideal for mid-IR light generation (full width at half maximum of ∼ 11 nm , compressed pulse duration of 230 fs) or a spectrum ideal for highly nonlinear processes such as high-harmonic generation ( - 10 dB level of &gt; 50 nm , transform-limited pulse duration of ∼ 65 fs ).

High-power Yb:CALGO regenerative amplifier and 30 fs output via multi-plate compression.

The pulse energy and average power are two long-sought parameters of femtosecond lasers. In the fields of nonlinear-optics and strong-field physics, they respectively play the role to unlock the various nonlinear processes and provide enough photon fluxes. In this paper, a high-energy and high-power Yb:CALGO regenerative amplifier with 120 fs pulse width is reported. This high-performance regenerative amplifier can work with high stability in a large tuning range of repetition rates. Varying the repetition rate from 3 to 180 kHz, the maximum output power of 36 W and the pulse energy up to 4.3 mJ, corresponding to a peak power of more than 20 GW are demonstrated. The output beam is near diffraction limited with M2 = 1.09 and 1.14 on the horizontal and vertical directions, respectively. In addition, multi-plate compression is employed to achieve 30 fs output with 23 W average power which is attractive for applications such as high-harmonic generation.

Ultrafast magnetic scattering on ferrimagnets enabled by a bright Yb-based soft x-ray source

Development of ultrafast table-top x-ray sources that can map various spin, orbital, and electronic configurations and reordering processes on their natural time and length scales is an essential topic for modern condensed matter physics as well as ultrafast science. In this work, we demonstrate spatiotemporally resolved resonant magnetic scattering (XRMS) to probe the inner-shell 4d electrons of a rare-earth (RE) composite ferrimagnetic system using a bright &gt; 200 e V soft x-ray high harmonic generation (HHG) source, which is relevant for future energy-efficient, high-speed spintronic applications. The XRMS is enabled by direct driving of the HHG process with power-scalable, high-energy Yb laser technology. The optimally phase-matched broadband plateau of the HHG offers a record photon flux ( &gt; 2 × 1 0 9 p h o t o n s / s / 1 % bandwidth) with excellent spatial coherence and covers the entire resonant energy range of RE’s N 4 , 5 edges. We verify the underlying physics of our x-ray generation strategy through the analysis of microscopic and macroscopic processes. Using a CoTb alloy as a prototypical ferrimagnetic system, we retrieve the spin dynamics, and resolve a fast demagnetization time of 500 ± 126 f s , concomitant with an expansion of the domain periodicity, corresponding to a domain wall velocity of ∼ 750 m / s . The results confirm that, far from cross-contamination of low-energy absorption edges in multi-element systems, the highly localized states of 4 d electrons associated with the N 4 , 5 edges can provide high-quality core-level magnetic information on par with what can be obtained at the M edges, which is currently accessible only at large-scale x-ray facilities. The analysis also indicates the rich material-, composition-, and probing-energy-dependent driving mechanism of RE-associated multicomponent systems. Considering the rapid emergence of high-power Yb lasers combined with novel nonlinear compression technology, this work indicates potential for next-generation high-performance soft x-ray HHG-based sources in future extremely photon-hungry applications on the table-top scale, such as probing electronic motion in biologically relevant molecules in their physiological environment (liquid phase), and advanced coherent imaging of nano-engineered devices with 5 ∼ 8 n m resolution.

Simple approach to broadband mid-infrared pulse generation with a mode-locked Yb-doped fiber laser.

Broadband mid-infrared (MIR) molecular spectroscopy demands a bright and broadband light source in the molecular fingerprint region. To this end, intra-pulse difference frequency generation (IDFG) has shown excellent properties among various techniques. Although IDFG systems pumped with 1.5- or 2-µm ultrashort pulsed lasers have been extensively developed, few systems have been demonstrated with 1-µm lasers, which use bulky 100-W-class high-power Yb thin-disk lasers. In this work, we demonstrate a simple and robust approach of 1-µm-pumped broadband IDFG with a conventional mode-locked Yb-doped fiber laser. We first generate 3.3-W, 12.1-fs ultrashort pulses at 50 MHz by a simple combination of spectral broadening with a short single-mode fiber and pulse compression with chirped mirrors. Then, we use them for pumping a thin orientation-patterned gallium phosphide crystal, generating 1.2-mW broadband MIR pulses with the -20-dB bandwidth of 480 cm-1 in the fingerprint region (760-1240 cm-1, 8.1-13.1 µm). The 1-µm-based IDFG system allows for additional generations of ultrashort pulses in the ultraviolet and visible regions, enabling, for example, 50-MHz-level high-repetition-rate vibrational sum-frequency generation spectroscopy or pump-probe spectroscopy.

Modeling of a high-power continuous wave Yb:YAG planar waveguide amplifier under thermal steady-state.

The performance of a novel, to the best of our knowledge, high-power Yb:YAG planar waveguide amplifier under thermal steady-state is studied numerically. We present a 3D thermal steady-state amplification model, which considers the effects of temperature on the Boltzmann occupation factors, pump absorption, and laser emission cross sections, in addition to reabsorption and pump saturation of Yb:YAG. The performance of a multipass-pumped planar waveguide amplifier under thermal steady-state was simulated considering the loss in the claddings, and a comparison with the simulated results under the ideal state was carried out. Our analysis results show that the core's temperature rise and the claddings' pump absorption lead to decreased pump absorption and optical-optical efficiencies. However, a high pump absorption efficiency (96%) and optical-optical efficiency (61.2%) are achieved when the pump power is 10 kW. Meanwhile, a lower fracture and minor thermal distortion can be expected in reality.

High-power Yb:YAG thin-disk laser with 80% efficiency pumped at the zero-phonon line.

We report a 3-kW thin-disk laser with 80% optical efficiency employing zero-phonon line pumping at 970 nm. A detailed comparison to conventional pumping at 940 nm is provided, which shows almost twice the pump power density handling capability.

High-power Yb:YAG thin-rod amplifier for use in a regenerative amplifier based on dual-slab Yb:KGW crystals

We present a hybrid chirped pulse amplification femtosecond laser amplification system with which to realize a Yb:KGW regenerative amplifier (RGA) and a Yb:YAG thin-rod amplifier. The combination of RGA based on dual Yb:KGW crystals and a thin-rod Yb:YAG amplifier with a high gain brings about output power up to 46 W before and 29.2 W after pulse compression down to 277 fs at a repetition rate of 200 kHz. The gain-narrowing effect was complemented by a combination of different types of gain-medium amplification. The results show that the output power of a Yb:KGW-based amplifier can be amplified simply by using a Yb:YAG thin-rod amplifier while suppressing the broadening of the pulse duration by gain narrowing.

Effect of Laser Treatment on the Surface Roughness of Multilayer Plasma Sprayed Thermal Barrier Coating System

Thermal barrier coatings (TBCs) are used in advanced engines working at higher temperatures. Higher efficiency and performance of gas turbine engines will require careful selection of TBCs. In this study, Ni22Cr10Al1.0Y (Amdry 9625) bond coat and two types of top coat including ceria stabilized zirconia (CSZ) ZrO2-24CeO2-2.5Y2O3) and yttria stabilized zirconia (YSZ) ZrO2-8Y2O3 were deposited on IN 625 by air plasma spraying (APS). The thickness of the duplex ceramic coat based on zirconia was in the range between 350 to 400 µm. The effect of high power Yb:YAG solid state laser at different laser parameters on feature, microstructure and roughness of plasma sprayed and laser sealed coating of multilayer ceria stabilized zirconia/ yttria stabilized zirconia was investigated. Surface roughness has been reduced significantly after laser sealing. The effect of laser process parameters carried out using Taguchi’s L16 orthogonal array design. Minimum roughness can be obtained at moderate power density and longer interaction time with sufficient specific energy to produce complete melting of coating. Characterization and analysis of results was achieved by employing scanning electron microscopy (SEM) , (EDS) and image J analysis. It was found from the results, there were significant improvements in the performance of plasma sprayed coatings after laser sealing due to the reduction of surface coating defects.

Sub-nanosecond, high peak power Yb:YAG/Cr4+:YAG/YVO4 passively Q-switched Raman micro-laser operating at 1134 nm

We demonstrate a sub-nanosecond, high peak power Yb:YAG/Cr4+:YAG/YVO4 passively Q-switched Raman micro-laser (PQSRML) operating at 1134 nm. The effect of transmission of the output coupler (TOC) and Cr4+:YAG initial transmission (T0) on the Raman laser performance have been investigated. Stable Raman laser pulse trains have been observed for Yb:YAG/Cr4+:YAG/YVO4 PQSRMLs with different combinations of output couplers and Cr4+:YAG crystals. Maximum average output power of Raman laser was 142.8 mW with TOC = 11% output coupler and T0 = 90% Cr4+:YAG. Enhanced Stokes pulse performance of 24.1 μJ, 45.1 kW, 535 ps was achieved with TOC = 16% and T0 = 85% Cr4+:YAG. A modified Raman laser rate equation model is established and the theoretically calculated results are in fairly good agreement with experimental results.

Optical properties of Li-based nonlinear crystals for high power mid-IR OPCPA pumped at 1 µm under realistic operational conditions

Optical properties of mid-infrared, Li-based nonlinear crystals (NLC) are estimated under realistic experimental conditions for high power lasers using the thermal imaging method. The study focuses on crystals with relatively large apertures for high energy and power applications that are transparent in a broad spectral range (6&#x2013;16&#x2005;&#x00B5;m). For this purpose, a high average power Yb:YAG laser amplifier system was used that pumps the crystals and the thermal response of the materials was recorded. An estimate of the linear and nonlinear absorption coefficients of different non-oxide crystals at the 1-&#x00B5;m pump wavelength along with their nonlinear refractive index is provided. To the best of our knowledge, linear and nonlinear absorption coefficients are presented for the first time, including the nonlinear refractive index of AGS, LGSe, LIS, and LISe. These optical material properties are of utmost importance for cutting-edge laser developments close to damage thresholds since they affect the resulting beam quality and conversion efficiencies of novel high power optical parametric amplifiers operating in the long-wavelength mid-infrared spectral range.

High-power narrow-linewidth single-frequency pulsed fiber amplifier based on self-phase modulation suppression via sawtooth-shaped pulses

Fiber laser system in master oscillator power amplifier (MOPA) scheme is a promising technique for high-power narrow-linewidth laser output. With modulation-generated pulsed seed laser, the fiber MOPA benefits the flexible temporal behavior. However, the spectral linewidth broadening induced by self-phase modulation (SPM) is the main obstacle to achieving high-power single-frequency laser output with narrow spectral linewidth, especially for pulsed fiber MOPA in which the kilowatts level peak power results in strong nonlinearity. The SPM induced linewidth broadening is related to the derivative of light intensity with respect to time (d&lt;i&gt;I&lt;/i&gt;/d&lt;i&gt;t&lt;/i&gt;). Theoretically, if the d&lt;i&gt;I&lt;/i&gt;/d&lt;i&gt;t&lt;/i&gt; of the laser pulse is a constant, the SPM process will not generate any new frequency components. Hence, the linewidth broadening can be suppressed. In this work, we demonstrate a high-power single-frequency Yb fiber amplifier at 1064 nm, in which a sawtooth laser pulse is employed to suppress the SPM induced linewidth broadening, for obtaining the output with near-transform-limited narrow linewidth. The sawtooth-shaped seed pulse train is generated through using an electro-optic intensity modulator to modulate the continuous-wave (CW) output of a single-frequency fiber laser. After being pre-amplified, the seed laser with a pulse repetition rate of 20 kHz is coupled into the main amplifier, in which a piece of 0.9-m-long Yb-doped silica fiber with core and clad diameters of 35 μm and 250 μm, respectively, is used as a gain medium. The seed laser is enhanced to an average power value of 3.13 W under a launched 976-nm pump power value of 11.3 W before the onset of stimulate Brillouin scattering. The pulse energy 157 μJ and the pulse width 6.5 ns give a peak power of 24 kW. The spectral linewidth measured using a scanning Fabry-Perot interferometer at the maximum power is only 83 MHz, which is quite close to the 76-MHz transform-limited linewidth of the 6.5-ns sawtooth-shaped pulse. For comparison, we also conduct an experiment with a common Gaussian-shaped seed laser, in which the spectral linewidth is broadened significantly with a peak power value of only 1.5 kW. The results here reveal that the using of the sawtooth-shaped pulse is a promising technique to suppress the SPM induced spectral linewidth broadening in high-peak-power fiber amplifiers and acquire near-transform-limited narrow-linewidth laser output.

High efficiency and compact Yb:YAG slab all-solid-state laser at room temperature

This paper presents the research progress of high efficiency and compact all-solid-state lasers based on Yb:YAG slab at room temperature. The laser dynamics model of Yb slab at room temperature is established. It is quantitatively analysed that the pumped laser intensity and the injected laser brightness influence the optical conversion efficiency. The method to suppress the slab-edge-effect is founded. The output power of 22.3 kW, the optical conversion efficiency of 36%, and the beam quality of 2.4 times diffraction limit, were achieved in experiment. These results lay a foundation for the key technology research of higher power laser and development of the miniaturized, lightweight and practical high power Yb slab laser.

Extreme Raman red shift: ultrafast multimode nonlinear space-time dynamics, pulse compression, and broadly tunable frequency conversion

Ultrashort high-energy pulses at wavelengths longer than 1 µm are now desirable for a vast variety of applications in ultrafast and strong-field physics. To date, the main answer to the wavelength tunability for energetic, broadband pulses still relies on optical parametric amplification (OPA), which often requires multiple and complex stages, may feature imperfect beam quality, and has limited conversion efficiency into one of the amplified waves. In this work, we present a completely different strategy to realize an energy-efficient and scalable laser frequency shifter. This relies on the continuous red shift provided by stimulated Raman scattering (SRS) over a long propagation distance in nitrogen-filled hollow-core fibers (HCF). We show a continuous tunability of the laser wavelength from 1030 nm up to 1730 nm with a conversion efficiency higher than 70% and high beam quality. The highly asymmetric spectral broadening, arising from the spatiotemporal nonlinear interplay between higher-order modes of the HCF, can be readily employed to generate pulses ( ∼ 20 f s ) significantly shorter than the pump ones ( ∼ 200 f s ) with high beam quality, and the pulse energy can further be scaled up to tens of millijoules. We envision that this technique, coupled with the emerging high-power Yb laser technology, has the potential to answer the increasing demand for energetic multi-TW few-cycle sources tunable in the near-IR.