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We report a high-power monolithic Tm:YAP microlaser dual-end-pumped by two fiber-coupled LDs emitting at 792 nm. The microlaser operated in the continuous wave (CW) mode, with a wavelength of 1,936.82 nm. We obtain a maximum output power of 37.8 W with a beam quality factor M2 of 9.6 at a total incident power of 174.9 W, corresponding to a slope efficiency of 29.2% and an optical–optical conversion efficiency of 21.6%. [ABSTRACT FROM AUTHOR]

• An optical-to-optical conversion efficiency of 5 % from 2.05 μm to 10.15 μm was achieved. • An new set of S-Es for BGSe crystal was derived. • NCPM BGSe OPO at long-wave infrared range was studied. In this letter, a non-critical phase-matching (NCPM) BaGa 4 Se 7 (BGSe) optical parametric oscillator (OPO) was demonstrated with a home-made acousto-optic (AO) Q-switched Ho:YLF laser as the pump source. The idler wavelength tunability was recorded to be 9393.3 to 10627.4 nm with BGSe crystal temperature varying from 45 to 5 Celsius (˚C), corresponding to an average wavelength adjustment of 30.85 nm/˚C. Up to 200 mW of idler average output power at 10219 nm was obtained with pulse repetition frequency (PRF) at 200 Hz, the slope efficiency and pump-to-idler efficiency are 8.04 % and 5 %, respectively. In addition, in the angle tuning experiment, a refined Sellmeier Equation (S-E) was derived based on the discrepancy between the experimental data and the theoretical calculations based on the existing S-Es. However, it was found that the deviations between experimental measurement data and theoretical calculations in NCPM experiment were still too large to be ignored after using the refined S-E. Probably, the phenomenon was caused by the thermo-optic dispersion formula dn/dT provided by references were not precise enough for describing NCPM BGSe crystal in waveband ∼ 10 μm. [ABSTRACT FROM AUTHOR]

We demonstrate a 2.09 μm Ho:YAG pulse power amplifier featuring high power, high efficiency, and low depolarization loss. By optimizing the gain medium structure, the maximum average output power of Ho:YAG amplifier was increased from 432 to 446 W with a seed power of 250 W. Wherein, the linearly polarized power was improved from 397 to 420 W, along with a decrease in depolarization loss from 0.082 to 0.058. At the maximum output power, the beam quality M2 factor was better than two times diffraction limited. The pulsewidth was ~ 50 ns at the pulse frequency repetition of 40 kHz. Furthermore, using the Ho:YAG laser as a pump source for a ZnGeP2 signal singly resonant optical parametric oscillator, the maximum output power was scaled to 151 W at the wavelength of 3.86 and 4.55 μm. [ABSTRACT FROM AUTHOR]

In this paper, we reported a 1,938 nm Tm:YAP slab laser pumped by two fiber coupled diode lasers, the maximum output power was 48.1 W at the incident pump power of 140 W, corresponding to the optical-to-optical efficiency of 34.4 % and slope efficiency of 43.6 %. The wavelength was selected at 1,938.8 nm by two etalons inserting in the cavity and the laser linewidth was 0.17 nm. The beam quality factors of $$M^{2}$$ were measured to be 3.5, 4.1 and 4.2 at the output power of 10, 25 and 35 W, respectively. [ABSTRACT FROM AUTHOR]

Abstract: Tm3+: GdVO4 and Ho3+: GdVO4 crystals with good optical quality were grown by Czochralski technique. Polarized absorption and unpolarized fluorescence spectra of Tm3+ and Ho3+ in GdVO4 crystals were measured. The Judd–Ofelt (JO) model was applied to obtain the three phenomenological intensity parameters. For Tm3+, Ω 2 =8.16×10−20, Ω 4 =2.45×10−20, Ω 6 =0.98×10−20 (with dimension of cm2). For Ho3+ Ω 2 =1.51×10−20, Ω 4 =1.61×10−20, Ω 6 =1.22×10−20 (with dimension of cm2). The radiative probabilities, radiative lifetimes, and branch ratios of Tm3+ and Ho3+ in GdVO4 crystals were then determined. Using the reciprocity method and Fuchtbauer–Ladenberg formula, the stimulated emission cross-sections for some interested transitions, such as (5F4, 5S2)→ 5I8 of Ho3+ and 1G4 → 3H6, 3H4 → 3F4 of Tm3+ in GdVO4, were determined and discussed. [Copyright &y& Elsevier]

A Tm,Ho:YVO 4 laser with compact geometry was demonstrated and analyzed. For the continuous wave laser, the slope efficiency of 30.5% was achieved. By inserting a Cr:ZnS saturable absorber into the cavity, the passively Q-switched laser generated almost constant pulse duration of 83 ns with the slope efficiency of 19.3%. The pulse energy was also independent of the pump power, around 130μJ. Through increasing the pump power from 3.7 W to 8.1 W, the pulse repetition varied approximately linearly from 2.9 kHz to 6.8 kHz. The Q-switch efficiency of the PQS laser is up to 58% at the maximum pump power. [ABSTRACT FROM AUTHOR]

In this paper, the thermal lens effect of dual-end-pumped Ho:YAG ceramic laser was studied experimentally and numerically. The thermal lens magnitude of Ho:YAG ceramic was obtained by beam quality inverse method. When the pump power increased from 9 to 88 W and the according pump radius increased from 0.2 to 0.25 mm, the thermal focal lengths in X and Y directions were decreased from 102 to 65 mm and 140 to 68 mm, respectively. Considering of the thermal lens, we further optimized the laser resonator with a concave-convex cavity and the slope efficiency was increased by 11.6 percent compared to the plane-concave cavity. [ABSTRACT FROM AUTHOR]

Pumped by a 100 W Q-switched Ho:YAG laser at 2090.7 nm with pulse repetition frequency of 10 kHz, four types of high-power long-wave infrared ZnGeP2 (ZGP) subsequent optical parametric amplifier (OPA) based on optical parametric oscillator (OPO) with different types of phase matching (PM) of ZGP crystals were demonstrated. For the results of 8.2 µm output characteristics at the full incident pump power, Type-II PM ZGP OPO with Type-II PM ZGP OPA had the best M2 of 1.8 and lowest average output power of 9.2 W with the narrowest linewidth of 77 nm, while Type-I PM ZGP OPO with Type-I PM ZGP OPA had the worst M2 of 2.2 and the widest linewidth of 122 nm, and Type-II PM ZGP OPO with Type-I PM ZGP OPA had the highest average output power of 12.6 W, corresponding to overall optical conversion efficiency of 12.6% from Ho to long-wave infrared laser system. [ABSTRACT FROM AUTHOR]

We demonstrate a single-longitudinal-mode Ho:GdVO4 continuous-wave (CW) laser at 2048.6 nm. We achieved excellent single-longitudinal-mode performance using a unidirectional ring cavity with an isolator and a half-wave plate. We obtain the maximum output power equal to 965 mW corresponding to a slope efficiency of 12.7%. [ABSTRACT FROM AUTHOR]

We demonstrate a comparative analysis of directly diode-pumped Tm3+-doped all-fibre laser operating at 1908 nm with different structure at fibre end facets. The feedback arising from parasitic oscillations and amplified spontaneous emission can be suppressed by coating an anti-reflection on the forward end facet and cleaving an angle on the backward end facet. 44.1 W laser power on forward end at the pumped power of 120 W was achieved. The forward laser slope efficiency was 39.3%, corresponding to the backward laser slope efficiency of 3.0%. The beam quality factor ofM2was 1.4. [ABSTRACT FROM PUBLISHER]

• A constant pulse duration Ho:YAG laser of 7 ns was realized, suppressing the gain dependence of pulse duration in Q-switched lasers. • A stable pulse train was obtained since the LGS has no significant piezoelectric ringing effect and thermally induced depolarization. • A reliable way to achieve high repetition rates and short nanosecond pulse durition for high power mid-IR ZGP OPO is provided. In this paper, we demonstrate a langasite (LGS) electro-optic Ho:YAG cavity-dumped laser that suppresses the gain dependence of pulse duration in Q-switched lasers. A constant pulse duration of 7.2 ns was achieved at a repetition rate of 100 kHz. Benefiting from the LGS crystal has no significant reverse piezoelectric ring effect and thermally induced depolarization, a stable pulse train was achieved at an output power of 43 W. For the first time, the application of cavity-dumped laser in mid-infrared (mid-IR) ZnGeP 2 (ZGP) optical parametric oscillator (OPO) has been realized, providing a reliable way to achieve high repetition rates and short nanosecond pulse times for high-power mid-infrared ZGP OPOs. The average output power was 15 W, corresponding to a pulse duration of 4.9 ns and a repetition rate of 100 kHz. [ABSTRACT FROM AUTHOR]

We present a 2.09 μm single-longitudinal-mode sandwich-type YAG/Ho:YAG/YAG ceramic laser pumped by a Tm-doped fiber laser for the first time. A pair of F-P etalons was used to achieve tunable single-longitudinal-mode operation. The maximum single-longitudinal-mode output power of 530 mW at 2091.4 nm was obtained with an absorbed pump power of 8.06 W, corresponding to an optical conversion efficiency of 6.6% and a slope efficiency of 12.7%. Wavelength tunable was achieved by tuning the angle of etalons and the wavelength could be tuned from 2091.1 nm to 2092.1 nm, corresponding to a tuning frequency of 68 GHz. The M 2 factor was measured to be 1.23. [ABSTRACT FROM AUTHOR]

We demonstrate a compact and efficient passively Q -switched (PQS) Ho:YLF laser pumped by a self-made all-fiber laser. Firstly, we design and make an all-fiber laser operating at 1940 nm with a slope efficiency of 40.6%. Then, the all-fiber laser was used to pump Ho:YLF laser directly. In the CW (continues-wave) operation Ho:YLF laser, the maximum output power was 7.79 W, corresponding to the slope efficiency of 55.2%. Using Cr 2+ :ZnS as the saturable absorber, the average power of 6.03 W was achieved with the slope efficiency of 45.9%. The shortest pulse duration was 15.6 ns and the pulse repetition frequency was 2.3 kHz at the pump power of 20.4 W. The pulse energy was a constant as 2.7 mJ when the pump power exceeded 15 W. The beam quality factor of M 2 was 1.05, indicating nearly diffraction limited beam propagation. [ABSTRACT FROM AUTHOR]

• Efficient 100W s-polarized Ho:YAG oscillator demonstrated, pumped by high-power Tm:YLF laser. • Orthogonal cylindrical lenses optimized 1.9 μm laser beam distribution within Rayleigh length. At maximum output, the beam quality factor was less than 1.6. A hundred-watt, linearly-polarized Ho:YAG oscillator, pumped by a 200 W, home-made and s- polarized Tm:YLF laser, was demonstrated. By utilizing a combination of a half-wave plate (HWP) and a thin-film polarizer (TFP), the Tm:YLF laser was split into two orthogonally polarized parts. Each part was significantly reshaped by a system of orthogonally arranged cylindrical lenses and subsequently used to dual-end pump the oscillator. With a total incident pump power of 183 W, a continuous wave (CW) output power of 101 W at 2.1 μm was achieved, with corresponding slope efficiency and optical-to-optical conversion efficiency (OOCE) of 61.6 % and 55.2 %, respectively. Additionally, the beam quality factors, measured in the x and y directions, were 1.59 and 1.35, respectively. Finally, under Q-switched operation at a repetition rate of 20 kHz, a maximum output power of 97 W was achieved, with a corresponding pulse width of less than 34 ns. The central wavelength of the laser was measured to be 2090.2 nm. [ABSTRACT FROM AUTHOR]

• The first report of a high-efficient Tm:YAP single crystal fiber laser, achieving a continuous output power of 20 W. • This SCF features undoped YAP end caps, innovatively bonded using a novel direct growth technique, overcoming the drawbacks of traditional thermal bonding. This approach ensures crystallographic alignment and reduces issues like joint cracking and interface defects, significantly improving the SCF's thermal management. We report the development of a low-loss, thulium-doped yttrium aluminum perovskite (Tm:YAP) single-crystal fiber (SCF), fabricated using the Czochralski method. This SCF features undoped YAP end caps that are directly grown on both ends, aimed at improving thermal management and enhancing the guidance of pump light. This innovative design also removes differences in crystallographic orientation, exhibiting a propagation loss of 0.0112 cm−1 at 1.94 µm. When pumped by diode lasers at 788 nm, the SCF laser delivers continuous-wave output powers of 11.9 W and 20.6 W under single-end and double-end pumping configurations, respectively. The slope efficiencies achieved are 53.2 % and 40.7 %, relative to the incident pump power. To the best of our knowledge, this is the inaugural report of a Tm:YAP SCF laser. [ABSTRACT FROM AUTHOR]

• Efficient, ultra-low threshold, mJ-level mid-infrared ZGP OPG. • Efficient, high-beam-quality mid-infrared ZGP OPG/OPA. • High-beam-quality mid-infrared double-pass ZGP OPG. In this paper, we demonstrated a high-efficiency mid-infrared ZnGeP 2 (ZGP) OPG/OPA system, operating at the mJ-level with hundred-picosecond pulses. The ZGP-based OPG configuration achieved a maximum pulse energy of 1.06 mJ at a repetition rate of 1 kHz, utilizing a pump pulse energy of 2.59 mJ and operating at a central wavelength of 3.9 μm. The system achieved a maximum slope efficiency of 51.1 %, leading to a corresponding total optical-to-optical conversion efficiency (OOCE) of 40.9 % and an output threshold as low as 0.046 GW/cm2. However, the beam quality factor M 2 deteriorated, reaching values above 45. To optimize the beam quality of the mid-infrared laser, we employed an OPG/OPA tandem configuration and a double-pass OPG configuration, resulting in maximum pulse energies of 0.85 mJ and 0.36 mJ, respectively. At the highest output energy, for the OPG/OPA tandem configuration, the beam quality factors M 2 were measured to be 3.2 in the x direction and 2.7 in the y direction. For the double-pass OPG configuration, the beam quality factors M 2 in the two directions were measured to be 3.5 and 3.2, respectively. [ABSTRACT FROM AUTHOR]

• A 1650 nm seed-injection, single-frequency Er:LuAG pulsed laser has been demonstrated in this paper, for the first time. • The maximum pulse energy of 2.15 mJ, pulse width of 225 ns under the pulse repetition frequency (PRF) of 200 Hz has been obtained. A 1650 nm seed-injection, single-frequency Er:LuAG pulsed laser with the double corner-cube-retroreflector (DCCR) structure has been demonstrated in this paper. In the total CCR structure (seed and slave laser), the maximum pulse energy of 2.15 mJ, with a pulse width of 225 ns under the pulse repetition frequency (PRF) of 200 Hz has been obtained, through the "ramp-hold-fire" injection-seeding technique. By utilizing the heterodyne technique, we have determined that the half-width pulse spectrum, which is 2.27 MHz. It is noteworthy that this marks the first successful realization of the 1650 nm single-frequency, Er:LuAG pulsed laser. [ABSTRACT FROM AUTHOR]

• A single-frequency all-PM HDF oscillator operating at 2.09 μm with an output power of 57.9 mW has been realized for the first time. To the best of our knowledge, this achievement represents the highest reported single-frequency power for a fiber oscillator at this wavelength. • The rapid switching of longitudinal mode states through FBG temperature tuning, as well as the optical bistability of longitudinal modes induced by saturable absorption, were recorded and discussed for the first time in the HDF oscillator. • A high-efficiency, high-polarization extinction ratio 2.09 μm single-frequency laser with a power of 1 W, generated through a first-stage HDF amplifier, serves as an optimal seed source for narrow-linewidth pulsed Ho:YAG solid-state lasers. We demonstrated a 2.09 μm single-frequency all-polarization-maintaining (all-PM) Ho-doped fiber (HDF) laser pumped by a 1940 nm Tm-doped fiber (TDF) laser. The oscillator employed a ring cavity scheme to enhance the net gain at the wavelength, with two circulators utilized to guarantee unidirectional laser operation and eliminate the spatial hole burning (SHB) effect in the gain fiber. An unpumped HDF was used as a fiber saturable absorber (FSA) to construct a powerful dynamic Bragg grating (DBG) for frequency selection. By optimizing the output coupling ratio, FSA length and FBG temperature, a maximum single-frequency output power of 57.9 mW was obtained with a center wavelength of 2089.73 nm. Furthermore, we recorded and discussed the rapid switching of longitudinal mode states through FBG temperature tuning, as well as the optical bistability of longitudinal modes induced by saturable absorption in the oscillator. Finally, a power level of 1 W with a polarization extinction ratio of 17 dB was successfully achieved by a first-stage HDF amplifier. [ABSTRACT FROM AUTHOR]

We demonstrated a 202 W Tm:YLF slab laser using a reflecting volume Bragg grating (VBG) as an output coupler at room temperature. Two kinds of active heat dissipation methods were used for the VBG to suppress the shift of wavelength caused by its increasing temperature. The maximum continuous wave (CW) output power of 202 W using the microchannel cooling was obtained under the total incident pump power of 553 W, the corresponding slope efficiency and optical-to-optical conversion efficiency were 39.7% and 36.5%, respectively. The central wavelength was 1908.5 nm with the linewidth (full width at half maximum) of 0.57 nm. Meanwhile, with the laser output increasing from 30 to 202 W, the total shift was about 1.0 nm, and the wavelength was limited to two water absorption lines near 1908 nm. The beam quality factors M2 were measured to be 2.3 and 4.0 in x and y directions at 202 W. [ABSTRACT FROM AUTHOR]

We reported an acousto-optic mode-locked Tm:LuAG laser pumped by a 786 nm laser diode and realized continuous-wave mode-locked operation. At the pump power of 8.2 W, the output average power was 335 mW with the wavelength of 2023.2 nm. The pulse width was 240 ps at the pulse repetition frequency of 81.60 MHz, and the beam quality factor M2 was 1.04. The output wavelength was tuned from 2022.6 to 2025.3 nm, corresponding to the output average power of 310 to 353 mW. In addition, the self-mode-locking phenomenon was found. [ABSTRACT FROM AUTHOR]

• We presented a gain-switched Ho,Pr:LLF laser pumped at 1191 nm for the first time. The maximum pulse energy of about 102 μJ at 2.95 μm and the minimum pulse width of about 33 ns were achieved with repetition rate of 20 Hz, corresponding to the peak power of about 3.1 kW. Furthermore, by using the gain-switched Ho,Pr:LLF laser as the pump source, the maximum energy of 6 μJ and the pulse width of the 5.5 ns was achieved in room temperature operation of the Fe:ZnSe laser, corresponding to the peak power of 1.2 kW. We demonstrate a room temperature operation narrow pulse width Fe:ZnSe laser pumped by a gain-switched Ho,Pr:LLF laser emitting at 2.95 μm in this paper. The gain-switched Ho,Pr:LLF laser produced the 102 μJ maximum pulse energy and 33 ns minimum pulse width, corresponding to the peak power of about 3.1 kW. Using this gain-switched Ho,Pr:LLF laser as the pump source, the maximum energy of 6 μJ at around 4.47 µm and the pulse width of 5.5 ns was achieved in the room temperature Fe:ZnSe laser, corresponding to the peak power of 1.2 kW. [ABSTRACT FROM AUTHOR]

Highlights • An intra-cavity Tm:YAG-Ho:SSO laser pumped at 1.6 µm was reported for the first time. • The Tm:YAG laser yields an output power of 9.7 W and a slope efficiency of 55.9%. • Ho:SSO laser yields output power of 4.9 W at 2116.5 nm and slope efficiency of 31.6%. Abstract In this paper, we have demonstrated an efficient intra-cavity pumped Ho:SSO laser based on a cascaded in-band pumping scheme for the first time. The laser diode at 1.6 µm was used to pump the Tm:YAG crystal. At an incident LD pump power of 18.7 W, dual end-pumped Tm:YAG laser provides the maximum output power of 9.7 W with a slope efficiency of 55.9%. With the same incident LD power, a maximum output power of 4.9 W at 2116.5 nm was achieved with a slope efficiency of 31.6% in the Ho:SSO laser intra-cavity pumped by a Tm:YAG laser. The beam quality factor of the Ho:SSO laser at maximum output level was measured to be 1.1 and 1.2 in the horizontal and vertical directions, respectively. [ABSTRACT FROM AUTHOR]

We proposed an injection-seeded Q-switched Ho: YLF laser by a tunable single-longitudinal-mode Tm, Ho: YLF laser. The tunable single-longitudinal-mode seed laser was achieved by inserting two Fabry-Perot (F-P) etalons in the Tm, Ho: YLF laser resonant cavity and changing the cavity length through a piezoelectric transducer (PZT). The wavelength of single-longitudinal-mode Tm, Ho: YLF laser could be tuned from 2050.962 nm to 2051.000 nm finely. The single-longitudinal-mode output power of 76 mW from Tm, Ho: YLF seed laser was achieved at the CO 2 absorption peak of 2050.967 nm. Single-frequency Q-switched Ho: YLF laser was achieved by injection seeding. The output energy of single-frequency Q-switched Ho: YLF pulse was 4.4 mJ, with a pulse width of 65 ns and a repetition frequency of 100 Hz. The beam quality factor M 2 of Ho: YLF laser was 1.07, nearly diffraction limit. The full width at half maximum (FWHM) of single-frequency pulse Ho: YLF laser measured by a heterodyne technique was about 4.1 MHz with the simultaneously recorded pulse width of 132 ns. [ABSTRACT FROM AUTHOR]

A CdSe optical parametric oscillator (OPO) was demonstrated to operate at 12.07 µm with a maximum output power of 170 mW at a pulse repetition frequency of 1.2 kHz pumped at 2.09 µm with 14.64 W from an acousto-optic Q-switched Ho:YAG laser. To the best of our knowledge, 12.07 µm is the longest wavelength obtained with a 2-μm laser-pumped CdSe OPO. Besides, the angular tuning curve for type II CdSe was also investigated, and the idler wavelength from the OPO could be tuned from 10.24 to 12.07 µm. [ABSTRACT FROM AUTHOR]

Ho:Lu3Al5O12(Lu AG) transparent ceramics are potential 2 μm eye-safe laser materials. Polycrystalline 0.8 at.% Ho:Lu AG ceramics with high optical quality were successfully fabricated by solid-state reactive sintering of high-purity oxide powders. The microstructure, the optical transmission, the spectrum characteristic, and the laser performance were investigated in this paper. The average grain size of Ho:Lu AG ceramics vacuum sintered at 1830°C for 30 hour is about 14 μm. The in-line transmittance of the sample is measured to be 81.7% and 82.0% at 1000 and 2250 nm, respectively. The absorption and the emission cross sections are calculated to be 0.88 × 10−20 cm2 at 1906 nm and 1.26 × 10−20 cm2 at 2094 nm. Using a thulium-doped yttrium-lithium-fluoride (Tm: YLF) laser with the central wavelength of 1907.5 nm as the pump source, 2.67 W continuous wave ( CW) laser operation at 2100.74 nm was obtained with a slope efficiency of 26.5%. The beam quality factor M2 was calculated to be 1.1, which indicated nearly diffraction-limited beam propagation and the laser was the fundamental TEM00 Gaussian mode. [ABSTRACT FROM AUTHOR]

In this paper, a ring cavity of Er:YAG laser with a single corner cube prism is investigated. Due to the depolarization effect of the corner cube, the tunable output coupling ratio was 0.25% to 72.67% by changing the angle of the λ / 4 plate according to the calculation results of Jones matrix. An experiment for checking the anti-detuning performances of the single corner cube cavity was also carried out. The results indicated that the output power was stable at the rotating angles of <3.06 deg and 1.637 deg along the vertical and horizontal directions, respectively. Under continuous wave operation, a 5.4 W vertically-polarized laser of 1645.1 nm was acquired through double polarizers with the beam quality factors (M2) of 1.17 in the x direction and 1.42 in the y direction, and the slope efficiency was 45.47%. Additionally, under the condition of a pulse-repetition-frequency (PRF) of 200 Hz, the pump power of 29.04 W, a maximum pulse energy of 2.2 mJ was realized, and the minimum pulse width was 86 ns, leading to a peak power of 25.58 KW. [ABSTRACT FROM AUTHOR]

• A 16.6 W continuous-wave Ho:GdVO 4 laser operating at room temperature is reported. • The peak power of Ho:GdVO 4 oscillator is up to 1.5 MW with a pulse repetition frequency of 1 kHz. • A linear polarized Tm:YAP solid laser is used as the pump source. We demonstrated a high-peak-power acousto-optically Q-switched Ho:GdVO 4 laser pumped by a linear polarized Tm:YAP solid laser. Adopting 0.5 at. % Ho:GdVO 4 crystals as the gain medium, the maximum continuous-wave output power was 16.6 W at 2048.5 nm with the incident pump power of 97.3 W, corresponding to a slope efficiency of 51.5%. When the pulse repetition frequency was 1 kHz, the maximum pulse energy of 10.7 mJ with a pulse width of 6.9 ns was obtained, corresponding to a peak power of 1.5 MW. To the best of our knowledge, this is the first demonstration of a Q-switched Ho:GdVO 4 laser with pulse energy exceeding 10 mJ, and the peak power reached a million-watt level. [ABSTRACT FROM AUTHOR]

We report the continuous wave and acousto-optically Q-switched operation of an in-pumped a-cut Ho:YAP laser at room temperature. We obtained a continuous-wave output power of 17.2 W at 2118 nm under an absorbed pump power of 29.8 W, corresponding to a slope efficiency of 63.2 %. For the Q-switched mode, we achieved a maximum pulse energy of about 1.7 mJ and a minimum pulse width of 24 ns at a repetition rate of 10 kHz, resulting in a peak power of 70.8 kW. [ABSTRACT FROM AUTHOR]

In this paper, more than 500g of high-purity ZGP polycrystalline material has been synthesized in one run, and high-optical quality ZGP single crystals with dimensions of 50mm in diameter and 140mm in length have been also successfully grown by Vertical Bridgman technique. From data of the near-infrared optical absorption coefficient, we found that the large crystal had lower absorption losses at the near-infrared waveband than the small one. Meanwhile, the absorption coefficient of 24-mm length ZGP–OPO devices for o-polarized 2.05µm light was significantly reduced to about 0.02cm−1 after thermal annealing and high energy electron irradiation. Moreover, improvement in the polishing of ZGP–OPO devices had resulted in increase of laser-induced damage threshold. The average value of laser-induced damage threshold was increased to 2.0J/cm2 under the condition of 2.05µm wavelength, 30ns pulse width and 10kHz pulse rate frequency. As a result, the maximum output of 20.5W was obtained by high pulse repetition frequency Ho:YAG laser emitting at 2.09µm under a pump power of 46W. The corresponding slope efficiency was 68.7% and the conversion efficiency was 44.3%. These results manifested that the large ZGP crystals with high optical quality were acceptable for the fabrication of the infrared OPO devices. [ABSTRACT FROM AUTHOR]

Abstract: The solid-state, tunable, narrowband, high pulse energy and high reliability lasers are attractive source for LIDAR system. In this paper, we demonstrated a diode pumped injection-seeded 2μm Tm:YAG laser. By inserting two F–P etalons into the laser cavity, linear-polarized single-frequency seed-laser was achieved at a wavelength of 2013nm, with a maximum output power of 60mW. Long-term and short-term frequency stability for the seed-laser were 1.27×10−7 and 97Hz/μs, respectively. High power Q-switched laser was operated using a bowtie cavity, the bidirectional output of which was favorable for the injection-seeded. After injecting the seed-laser to the power-laser, single-frequency, nearly transform-limited pulsed 2μm laser was obtained. As much as 2.0mJ output energy was achieved at an operating repetition rate of 15Hz, with a pulse width of 356.2ns. [ABSTRACT FROM AUTHOR]

Abstract: The growth of ZnGeP2 crystals by seeded Vertical Bridgman method was studied. High-quality near-stoichiometric ZnGeP2 single crystals obtained were of 20–30mm in diameter and 90–120mm in length. By selection of the seed crystallographic orientation the single crystal ingots without cracks and twins were grown, as shown by X-ray diffraction. The infrared transmission property of the ZnGeP2 crystals was studied by the calculated optical absorption coefficient spectra. The results showed that after thermal annealing of the crystals the optical absorption coefficient was ∼0.10cm−1 at 2.05μm, and ∼0.01cm−1 at 3–8μm. The rocking curves patterns of the (400) reflection demonstrated that the as-grown single crystals possessed a good structural quality. The composition of the crystals was close to the ideal stoichiometry ratio of 1:1:2. The low-loss typical ZnGeP2 samples of 6mm×6mm×15mm in sizes were cut from the annealed ingots for optical parametric oscillation experiments. The output power of 3.2W was obtained at 3–5μm when the incident pumping power of 2.05μm laser was 9.4W, and the corresponding slope efficiency and the conversion efficiency were 44% and 34%, respectively. [ABSTRACT FROM AUTHOR]

Abstract: A high optical quality Ho3+-doped lutetium orthosilicate laser crystal Lu2SiO5 has been grown by the Czochraski method and the accurate concentration of Ho3+ ions in the crystal was measured. The polarized absorption spectra, polarized fluorescence spectra and fluorescence decay curve of Ho3+ ions in the Lu2SiO5 crystal were measured at room temperature. Based on the Judd–Ofelt model, three effective intensity parameters were determined as: =4.57×10−20 cm2, =3.11×10−20 cm2, =1.42×10−20 cm2. The fluorescence lifetime of the 5 I 7 manifold for Ho3+ ions was measured to be 3.3ms and the quantum efficiency was estimated. The polarized emission cross-sections for the 5 I 7 → 5 I 8 transition were determined by Fuchtbauer–Ladenburg formula. The good spectroscopic properties imply that Ho: Lu2SiO5 crystal is a potential laser gain medium for 2μm lasers. [Copyright &y& Elsevier]

• A rectangular ring cavity CdSe pulsed-nanosecond OPO output of 1.18-W average power at ~11 μm is reported. • A linear cavity CdSe pulsed-nanosecond OPO output of 1.03-W average power at ~10.15 μm is reported. • OPO is a promising method to obtain high average output power in the range 8–12 μm from a CdSe crystal. • Before 2018, OPO was used to trying to obtain high average power in 8–12 μm from CdSe crystal. However, due to the low optical-to-optical conversion efficiency, the maximum average output power only reached 320 mW near 10 μm. Slowly, the OPO method tends to be abandoned. In 2020, the seed-injection method instead of OPO was used to achieve high average power output. Because of the fascinating simplicity and stability of the OPO method, we insisted on using OPO to achieve high power and succeeded in obtaining watt-level average power in 8–12 μm. Compared to previous OPO method, the improvement of average output power is about ~265%. Compared to seed-injection method, the the average output power improvement at 11 μm is about ~50%. For the first time, >1 W at ~11 μm laser was achieved. Therefore, OPO is still a promising method to obtain high average power 8–12 μm lasers. In this paper, using two cadmium selenide (CdSe) crystals, we have demonstrated signal-resonant pulsed-nanosecond optical parametric oscillators (OPOs) in linear and rectangular ring cavity designs with output powers of up to 1.03 W at 10.15 μm (idler) and 1.18 W at 11 μm (idler) were obtained, respectively. A Q-switched Ho:YAG laser at 2.09 μm with a pulse repetition frequency of 1 kHz was used as the OPO pump source. At the maximum output power level of the idler at 10.15 μm, the corresponding slope efficiency and optical conversion efficiency were 5.22% and 2.33%, respectively, with a spatial beam quality of M 2 < 10.8. Similarly, we also recorded the slope efficiency and optical conversion efficiency at 11 μm to be around 5.38% and 2.73%, respectively, with a spatial beam quality of M 2 < 5.1. The idler wavelength is tunable in the 10.2–10.05-μm range for the linear cavity OPO with output power varying from 0.98 W at 10.2 μm to 1.09 W at 10.05 μm by varying the internal crystal angle from 72.7° to 73.39°. Similarly, the wavelength tunability of the idler was recorded to be 11.2–10.9 μm for the rectangular ring cavity OPO with output power varying from 1.04 W at 11.2 μm to 1.26 W at 10.9 μm by varying the internal crystal angle from 69.6° to 70.39°. [ABSTRACT FROM AUTHOR]

• A 105 W continuous-wave (CW) diode-pumped Tm:YAP slab laser operating at room temperature is reported. • The beam quality factors M2 at the highest output power are 2.76 and 2.78 in the x and y directions, respectively. • A theoretical model is presented to predict the characteristics of the hundred-watt-level Tm:YAP laser. We demonstrated a high power and good beam quality continuous-wave (CW) Tm:YAP slab laser operating at room temperature. Two fiber-coupled laser diodes were used as pump source, the maximum output power of 105 W at 1936.4 nm was achieved with the total incident pump power of 308 W, corresponding to the slope efficiency and optical-to-optical efficiency were 41.4% and 34.1% with respect to the incident pump power, respectively. At the maximum output power, the beam quality factors M2 were 2.76 and 2.78 in the x and y directions, respectively. Besides, a theoretical model was presented to predict the temperature distribution, thermal induced stress and laser performance of the Tm:YAP slab laser, and the experimental results were consistent with the theoretical simulation results which indicated that this model could simulate hundred-watt-level Tm:YAP lasers well. [ABSTRACT FROM AUTHOR]

A free-running Fe:ZnSe laser is demonstrated under the pump of a single-shot 2.94 μm Er:YAG laser along the cavity axis at liquid nitrogen temperature of 77 K. At the incident pump energy of 1.47 J, a maximum single pulse energy of 253.7 mJ is obtained with a minimum pulse duration of 92.4 μs, corresponding to a slope efficiency of 16.2%. The central wavelength and the full width at half maximum (FWHM) are 3944.7 and 68.4 nm, respectively. [ABSTRACT FROM AUTHOR]

We demonstrated a first continuous-wave and acousto-optical Q-switched Ho:YAP laser pumped by fiber-coupled laser diode at 1.91 µm. With a dual-end wing-pumping scheme, a maximum continuous-wave output power of 10.5 W at 2.1 µm and a slope efficiency of 53.2% were obtained when the incident LD power was 25.6 W, while diode-to-Ho conversion efficiency reached up to 41.0%. The Q-switched Ho:YAP laser was investigated for different pulse repetition frequencies from 3 to 20 kHz. The maximum average output power of 9.8 W and maximum pulse energy of 2.7 mJ were achieved at pulse repetition frequencies of 20 and 3 kHz, respectively. In addition, we demonstrated an efficient mid-infrared laser based on a diode-Ho-ZGP architecture for the first time. With a pulse repetition frequency of 3 kHz and an incident Ho pump power of 8.2 W, the average output power of 4.8 W and slope efficiency of 61.0% were reached in mid-infrared ZGP-OPO. [ABSTRACT FROM AUTHOR]