Search

Realizing high average power nanosecond pulsed single longitudinal mode laser sources around 1.6 μm are of intense interest for applications as diverse as range finding, remote sensing, and environmental monitoring. Herein, we first demonstrate a high average power and high beam quality nanosecond pulsed eye-safe diamond Raman laser at 1634 nm, which is intracavity driven by an acousto-optic Q-switched two-crystal Nd:YVO4 laser at 1342 nm. By exploiting the subtly designed dynamically stable resonator and the thoroughly optimized acousto-optic modulator, excellent beam quality and substantial power improvement have been confirmed. Under the incident pump power of 60.9 W, the highest multimode average output power of 6.92 W has been achieved with the repetition rate of 25 kHz and the duty cycle of 8%, corresponding to the pulse duration of 8.8 ns and the peak power of 31.5 kW. Subsequently, by inserting a fused silica etalon in the high-Q fundamental cavity, the average output power for single longitudinal mode operation has been creeping up to 2.56 W with the aid of the high precision temperature controlling and the enlarged beam diameter on diamond, where the pulse duration and the spectral linewidth are 8 ns and 180 MHz, respectively. The beam quality is maintained with M2 < 1.3 across the entire output power range.

The photonic crystal surface-emitting laser (PCSEL) has attracted much attention due to the advantages of a small far-field divergence angle and high output power. Here, we report a high-power terahertz (THz) photonic crystal laser with high beam quality through the optimization of the absorption boundary condition and the introduction of the symmetrically distributed electrodes. Single-mode surface emission at 3.4 THz with the maximum peak output power of 50 mW is demonstrated. Meanwhile, a high symmetric far-field pattern with C6 symmetry and a small divergence angle is achieved. In this device, the integration of the stable single-mode operation, high beam quality and high output power is realized, which may have great significance for practical applications. [ABSTRACT FROM AUTHOR]

In this study, we investigated the influence of fiber parameters on stimulated Raman scattering (SRS) and identified a unique pattern of SRS evolution in the counter tandem pumping configuration. Our findings revealed that the SRS threshold in counter-pumping is predominantly determined by the length of the output delivery fiber rather than the gain fiber. By employing the counter tandem pumping scheme and optimizing the fiber parameters, a 10 kW fiber laser was achieved with beam quality M2 of 1.92. No mode instability or severe SRS limitation was observed. To our knowledge, this study achieved the highest beam quality in over 10 kW fiber lasers based on conventional double-clad Yb-doped fiber.

The photonic crystal surface-emitting laser (PCSEL) has attracted much attention due to the advantages of a small far-field divergence angle and high output power. Here, we report a high-power terahertz (THz) photonic crystal laser with high beam quality through the optimization of the absorption boundary condition and the introduction of the symmetrically distributed electrodes. Single-mode surface emission at 3.4 THz with the maximum peak output power of 50 mW is demonstrated. Meanwhile, a high symmetric far-field pattern with C6 symmetry and a small divergence angle is achieved. In this device, the integration of the stable single-mode operation, high beam quality and high output power is realized, which may have great significance for practical applications.

It is very challenging to make high peak power (big pulse energy) Raman lasers compact, due to laser induce breakdown (LIB) effect; and it is even more difficult to achieve a decent beam quality meanwhile. In this work, a pulsed 1064 nm laser was used as pump source; pressurized methane was used as Raman active medium, which had the largest ratio of backward/forward Raman gain coefficient among all gaseous media; and backward first Stokes (BS1) Raman laser of 1543 nm with good beam quality was realized. When an f=0.5 m lens was used to focus pump beam into a 0.9 m long Raman cell filled with 3.5 MPa methane, 276.1 mJ BS1 was achieved, the corresponding photon conversion efficiency was 70.8% and the peak power was 83.7 MW. BS1 beam quality was measured to be M x 2=2.54,M y 2=2.28, which was significantly better than that of pump laser. In a setup of f=0.3 m focal lens and 0.5 m long Raman cell, 197.8 mJ BS1 was achieved, with the company of serious LIB. In order to meliorate LIB and improve BS1 conversion efficiency, the focal lens was tilted by 20°, pump laser beam waist and depth of focus increased significantly, BS1 was improved to 225.0 mJ, the corresponding photon conversion efficiency was 58.5%. An even short focal lens and Raman cell with reasonable BS1 energy was possibly achieved by tilting a shorter focal lens by a larger angle. This work also demonstrated that the increment of BS1 conversion may help to reduce the effect of LIB on SRS process. [ABSTRACT FROM AUTHOR]

This work demonstrates the generation of short pulse duration and high-beam-quality laser pulses using transient stimulated Brillouin scattering at a high repetition rate. Thermal effects and optical breakdown are identified as the main factors that restrict energy reflectivity and beam quality under high repetition rates and transient situations. Through experimental analysis, the interaction length and focal point size are determined to be the key parameters in reducing the thermal effect by reducing the absorption of the laser pulse by the medium. The obtained results show that pulses with a duration of 175 ps and beam quality M² of around 1.2 can be achieved with a maximum energy reflectivity of over 40% under an interaction length of 50 mm. Furthermore, at an interaction length of 90 mm, a pulse output with a minimum duration of 115 ps (0.5τQ) is achieved. [ABSTRACT FROM AUTHOR]

Tm3+:YAP lasers in-band fiber-laser pumped at 1670 nm with a linear or L-shaped cavity were studied in CW, actively and passively Q-switched regimes. High-efficiency CW and repetitively-pulsed operations were registered at three spectral regions: 1987â€"1994 nm, 1935â€"1941 nm and 1892â€"1897 nm. The transition between these three spectral regions was achieved by controlling the pump power and the output mirror in a laser cavity. The highest CW output power that was achieved without degrading the beam quality was 12.2 W at the 52% slope efficiency with respect to the incident pump. Acousto-optically Q-switched operation with the average power of 9.8 W at the 20 kHz pulse repetition rate (PRR) and 6 W at 3 kHz PRR was achieved, the pulse energy was scaled up to 2.7 mJ at 0.5 kHz PRR. The passive Q-switch operation at 1935â€"1938 nm was obtained using a Cr2+:ZnSe saturable absorber; the pulse energy reached 150 µ J at the 20 kHz PRR [ABSTRACT FROM AUTHOR]

• The use of fused silica as an all-solid-state SBS-PCM significantly improves the beam quality factor from 1.23 to 1.085 times the diffraction limit. • The SBS-PCM system achieved a maximum output energy of 672 mJ from an input energy of 75.2 mJ, demonstrating a substantial magnification of approximately 9 times. • The SBS-PCM effectively mitigates unfavorable diffraction patterns induced by the hard-edge aperture, leading to a more uniform beam profile. • The coefficient of determination (R 2) of the beam profile improved by 2.18% compared to that of the high-reflection mirror. Beam quality is critical for laser applications in both scientific and industrial fields. Stimulated Brillouin scattering phase conjugate mirror (SBS-PCM) serves as an effective beam cleanup scheme due to its phase conjugation properties. In this work, a SBS-PCM using fused silica was constructed and employed in a double-pass amplifier setup. With an input energy of 75.2 mJ, the system achieved a maximum magnification of approximately 9 times, resulting in an output energy of 672 mJ. Comparative analysis with a high-reflection mirror revealed that the SBS-PCM effectively mitigated unfavorable diffraction patterns induced by the hard-edge aperture in the near-field pattern, improving the beam quality factor from 1.23 to 1.085 times the diffraction limit. Additionally, the coefficient of determination (R 2) of the beam profile improved by 2.18 % compared to that of the high-reflection mirror. These results indicate that the free-space all-solid-state SBS-PCM can provide a promising approach to improving beam quality for high-power laser systems. [ABSTRACT FROM AUTHOR]

Highlights • A high beam quality narrow linewidth μs-pulse Ti:sapphire laser is firstly obtained. • Such μs 819.710 nm laser is well suited to generate a polychromatic laser guide star. • A 3 W 819.710 nm laser is generated by a frequency-doubled 1064 nm Nd:YAG laser. • The laser is operating at 500 Hz repetition rate with pulse width of ∼25 μs. • The linewidth of the laser is 0.8 pm with M2 = 1.14. Abstract A sub-pm linewidth high beam quality microsecond (μs) Ti:sapphire laser was reported, which was end-pumped by a frequency-doubled 1064 nm Nd:YAG laser. By inserting three birefringent plates tuner and one etalon into the cavity of the Ti:sapphire laser, a ∼ 0.8 pm linewidth at 819.710 nm was achieved with a maximum output power of 3 W operating at a high repetition rate of 500 Hz with pulse width of ∼25 μs. The beam quality factor M2 was measured to be ∼1.14. The wavelength could be finely tuned from 819.699 to 819.718 nm with tuning resolution of 0.76 pm. To the best of our knowledge, this is the first demonstration on the μs pulse Ti:sapphire laser at 819.710 nm with narrow linewidth and high beam quality simultaneously. Such μs 819.710 nm laser could be used to efficiently generate a polychromatic laser guide star together with a 589 nm laser for the tip-tilt correction of ground-based telescopes. [ABSTRACT FROM AUTHOR]

Abstract A high-beam-quality and high-energy long-pulse laser has been developed with VRM(variable reflectivity mirror)coupling and spherical aberration compensation. The thermal lens and the thermal birefringence are compensated for by the 10 mm DL rod side-pumped laser module. The output mirror employs VRM coupling with R=35% in the center, which presents a energy of 1.04 J at a pulse width of 195 μs and a repetition rate of 400 Hz with a beam quality of M2≈8.4. The spherical aberration compensation improves the beam quality M2 factor to 2.15; the power stability (RMS) is 0.4% at 5 min, and the optical-optical efficiency is 19.7%. [ABSTRACT FROM AUTHOR]

We present a compact diode side-pumped continuous-wave (CW) Tm,Ho:YAG laser oscillator with high brightness at 2. 09 μ m. After carefully optimizing the system elements, this laser delivers a maximum output power of 21.9 W with an optical-to-optical efficiency of 6% at a temperature of 12 °C. The average beam quality is measured to be M 2 = 3. 17 , leading to a brightness value of up to 50 MW/cm2 ⋅ sr. To the best of our knowledge, this represents the highest brightness for any Tm,Ho co-doped laser oscillators operating at near-room temperature (NRT). • High brightness 2. 09 μ m Tm,Ho:YAG laser operating at near-room temperature. • Achieving a maximum output power of 21.9 W with a beam quality factor M 2 of 3.17. • Design of a compact side-pumped laser head with uniform pump distribution. • Implementation of a thermally near-unstable cavity design for a large mode volume. [ABSTRACT FROM AUTHOR]

In this study, efficient third harmonic generation was investigated by employing a delay line and LiB 3 O 5 (LBO) crystals with 600 fs pulse lasers at 1030 nm. We systematically investigated the differences in the frequency conversion of the LBO crystals for second and third harmonic generation with varying beam spots. Specifically, it has been demonstrated that the inclusion of a delay line is necessary to mitigate the group velocity mismatch at hundreds femtosecond laser. The results indicate that the maximum output powers are approximately 16.5 W and 5.6 W at wavelengths of 515 nm and 343 nm, respectively. The corresponding optimal conversion efficiencies are 59.6 % (from 1030 nm to 515 nm) and 20.4 % (from 1030 nm to 343 nm). And the beam quality has improved noticeably at 515 nm (M x 2 = 1.16, M y 2 = 1.13) and 343 nm (M x 2 = 1.16, M y 2 = 1.12), in contrast to that at 1030 nm (M x 2 = 1.56, M y 2 = 1.49). • High efficiency and high beam quality THG by employing LBO crystals is obtained. • The effectiveness of a delay line for THG of hundreds femtosecond laser is demonstrated. • Different focusing lenses on LBO crystals to stimulate SHG and THG are discussed. • The effects of different types of LBO crystals for THG are investigated. [ABSTRACT FROM AUTHOR]

In this paper, we report on high beam quality vertical-cavity surface-emitting lasers (VCSELs) featuring a monolithically integrated aspherical microlens. This lens is fabricated by a one-step diffusion-limited wet etch process. VCSELs with microlenses with different curvature radius are designed, fabricated, and characterized, as well as reference VCSEL devices without the microlens. Significant improvement of beam divergence and single-mode performance are demonstrated in microlens VCSELs. The divergence angles of a conventional VCSEL are 14.5°, 16.0°, and 17.0° (full width at D4σ) at 2 mA, 3 mA, and 4 mA, respectively, with a M2 value measured to be 6.9 at 3 mA. Under the same current injection, the divergence angles of a comparable VCSEL with a micro-lens (curvature radius of 31.8 μm) are reduced to 4.8°, 5.5°, and 5.7°, respectively. The M2 value of the lensed VCSEL is as low as 1.9 at 3 mA.

• A high-stability high-peak-power near-diffraction-limit 1-kHz sub-nanosecond diode-end-pumped Nd:YAG laser amplifier was achieved. • The single pulse energy was amplified from 80 μJ to 2.72 mJ (34 times magnification) by a single-stage double-pass MOPA configuration. • The evolution of thermal effects to degrade the laser beam quality of the amplifier was numerically analyzed, and a spherical-aberration self-compensated scheme was designed. A high-beam-quality 1-kHz sub-nanosecond Nd:YAG master oscillator power amplifier (MOPA) system based on diode end pumping is demonstrated. Based on detailed theoretical analysis on thermal effects in the gain medium, especially the spherical aberration which played the major role in beam degradation, a simple and effective compensation scheme was designed for the experiment. While the single pulse energy was amplified from 80 μJ (oscillator) to 2.72 mJ (amplifier, 34 times magnification), the beam quality factor (M2) was improved from 1.21 to 1.14 at the same time. The evolution of pulse duration with the increase of pump power was also investigated. The output pulse width of 454 ps corresponded to the peak power of 6 MW, the highest in kHz-level end-pumped single-stage Nd:YAG amplifiers up to now. The MOPA system demonstrated excellent operating stability, with the peak-to-peak and root-mean-square (RMS) power fluctuation of 2.78 % and 0.54 %, respectively. [ABSTRACT FROM AUTHOR]

In this paper, we report on high beam quality vertical-cavity surface-emitting lasers (VCSELs) featuring a monolithically integrated aspherical microlens. This lens is fabricated by a one-step diffusion-limited wet etch process. VCSELs with microlenses with different curvature radius are designed, fabricated, and characterized, as well as reference VCSEL devices without the microlens. Significant improvement of beam divergence and single-mode performance are demonstrated in microlens VCSELs. The divergence angles of a conventional VCSEL are \text14.5°, $16.0$°, and $17.0$ ° (full width at D4$\sigma$ ) at 2 mA, 3 mA, and 4 mA, respectively, with a $M^2$ value measured to be 6.9 at 3 mA. Under the same current injection, the divergence angles of a comparable VCSEL with a micro-lens (curvature radius of 31.8  $\mu$m) are reduced to $4.8$°, $5.5$ °, and $5.7$ °, respectively. The $M^2$ value of the lensed VCSEL is as low as 1.9 at 3 mA. [ABSTRACT FROM PUBLISHER]

We demonstrate an acousto-optic Q-switched LED-pumped laser with high repetition rate and beam quality with a compact linear cavity. By optimizing design of the LED-pumped Nd:YAG rod laser, a maximum average power of 2.5 W at 1063.92 nm laser with duration of 1.34 μs is achieved, corresponding to an optical efficiency of 8% and a slope efficiency of 10.7%. After optimizing the resonator configuration with an acousto-optic Q-switched modulation, a 1.2 W average output power of pulsed laser with duration of 296 ns is obtained with a peak power of 810 W at a repetition rate of 5 KHz. The beam quality factors of M x 2 = 2.12 and M y 2 = 1.77 are obtained through mode selection by pinhole. To the best of our ability, this is the best high repetition rate and beam quality of an acousto-optic Q-switched LED pumped laser oscillator with watt-level output reported so far, which means that LED pumped solid-state lasers will make breakthroughs in various scientific and technological applications. • First demonstration of a LED-side-pumped acousto-optic Q-switched Nd:YAG rod laser with high repetition rate and beam quality operation. • Realize Watt-level actively Q-switched laser with LED-pumped Nd:YAG module for the first time. • Explore the new technical scheme to realize more efficient LED-pumped Nd:YAG module. [ABSTRACT FROM AUTHOR]

A joule-level Nd:YAG nanosecond laser of high repetition frequency and high beam quality is developed out. The laser is designed as a MOPA system mainly including single longitudinal mode seed, pre-amplifier unit an d power amplifier unit. In order to obtain the high-quality laser beam output, phase conjugation is adopted to compensate the laser beam distortion. Under the condition of 200 Hz high repetition frequency and 8.19 μJ single pulse energy injected by the single longitudinal mode seed, 1.53 J output energy is gained. The output laser beam is of 9 mm diameter, 7.41 ns pulse width, the far field beam spot 1.32 times the value of the diffraction limit, 1.2% energy stability (RMS) and less than 13 μrad far field beam spot angle shift. [ABSTRACT FROM AUTHOR]

• The first demonstration of a monolithic counter tandem pumped ytterbium-doped fiber amplifier based on conventional double-clad fiber. • The maximum output power of 5.03 kW is achieved with near single-mode beam quality (M2 = 1.54). No SRS or TMI appear. • The impact of the 1080 nm signal laser from the amplifier on 1018 nm pump sources is investigated. • Optimizations of pump sources capable of being adapted to counter tandem pumping are given. We report on what we believe is the first demonstration of a monolithic counter tandem pumped ytterbium-doped fiber amplifier based on conventional double-clad fiber. At the maximum power of 5.03 kW, the amplifier delivered a near single-mode beam quality (M2 = 1.54), without stimulated Raman scattering effect or mode instability. In addition, we theoretically and experimentally investigated the impact of the 1080 nm signal laser from the amplifier on the 1018 nm fiber lasers used as pump sources. It revealed that even a small proportion of signal light coupled into a 1018 nm fiber laser cavity could cause a considerable power decline of the pump laser. Possible solutions to reduce the influence of signal light on pump sources were extensively discussed. Moreover, we experimentally confirmed the advantage in nonlinear effects mitigation of counter-pumping compared to co-pumping. This work proves the feasibility and superiority of the all-fiberized counter tandem pumping scheme, which could provide inspiration for future power scalability. [ABSTRACT FROM AUTHOR]

GaAs-based narrow-stripe broad-area lasers with integrated surface gratings are shown to operate with high power and efficiency, low beam parameter product (BPP), and narrow spectra. These distributed feedback lasers are constructed using a surface-etched, 80th-order grating, leading to spectral width \Delta\lambda95\%<0.7~nm (95% power) and wavelength \sim\rm970~nm. Optical output powers (>6~W) and power conversion efficiencies (>50\%) comparable with devices without grating are enabled by a small coupling coefficient, \kappaL\sim0.3, consistent with coupled mode theory calculations. The lasers were constructed with a stripe width of 30 \mum, enabling BPP <1.8~mm mrad up to 6-W output power, improved over devices without gratings, that show BPP >2.2~mm mrad. We attribute the improvement to spatial filtering of higher order lateral modes by the narrow surface grating. Such devices are attractive sources for use in spectral beam combination systems for material processing. [ABSTRACT FROM PUBLISHER]

Since their invention in 1966 copper vapour lasers (CVLs) have developed into a mature technology with applications including high-speed imaging, micro-machining, non-linear frequency conversion to the ultraviolet, and pumping of solid-state laser materials. However, the performance characteristics of conventional CVLs are fundamentally limited by kinetic processes at play within the gain medium and hence, these devices largely failed to keep pace with advances in visible solid state lasers during the late 1980s and early 1990s. In 1996 a new subclass of CVL, termed a kinetically enhanced or KE-CVL, was developed that used a ternary gas mixture (HCl–H2–Ne) to tailor the kinetic processes that limit laser performance. These devices offer dramatic improvements in power (both average and high beam quality) and repetition rate scalability. Indeed, 100 W of visible, high beam quality power is now readily available from relatively small copper laser systems. In this paper the underlying principles and performance characteristics of KE-CVLs will be reviewed. [Copyright &y& Elsevier]

Two-dimensional in-phase coherently coupled vertical cavity surface emitting laser (VCSEL) array with high beam quality was fabricated by proton implantation. Indium-tin-oxide (ITO) current spreading layer was employed to improve the uniformity of the injection current. This makes a coherent array to operate in in-phase mode even in a relatively larger scale. The appropriate thickness of ITO current spreading layer was obtained by experiment (80 nm). The procedure of proton implantation defined array is considerably simple and low cost. A 3 × 3 in-phase coherently coupled array with 2.4° (1.28 × D.L.) of lobe beamwidth was achieved. It sufficiently demonstrates the advantages of the high beam quality of the in-phase coherently coupled arrays. The output power of the array was up to 4.5 mw under pulse-wave condition.

Two-dimensional coherently coupled arrays of vertical cavity surface emitting lasers were fabricated using proton implantation. A 2 × 2 array with the far field beamwidth of 3.6° ( 1.18×diffraction limited), the output power of 0.45 mW, and the spectral line width of 0.2 nm was achieved for continuous wave operation at room temperature. It showed an excellent beam quality due to the in-phase coupling among the elements in the array. The array performance dependence on injection current level and thermal effects was discussed. The processing for the arrays is considerably simple and can be used as an alternative to other array implementations. [ABSTRACT FROM PUBLISHER]

It was proposed and demonstrated that a high beam quality self-pulse could be achieved by off-axis feedback for 1.95-μm GaSb-based broad-area laser. The comparative studies of on-axis feedback and off-axis feedback were conducted in an experiment. A highly reflecting (HR) mirror with sharp edge was used in the off-axis feedback system and the overlapping size was changed by moving the HR mirror. At the direct current of 1.8 A, 45-cm external cavity length, and 36% strength of feedback, the off-axis feedback with the overlapping size of 1.2 mm could accomplish the regular periodic pulse with the frequency of 153 MHz. The beam quality M2 was 12.75 in slow axis and improved nearly doubled compared with that in the on-axis feedback system. [ABSTRACT FROM AUTHOR]

A novel laser-coupling structure is introduced, in which the same transmission grating is simultaneously employed by two spectral beams generated in identical resonant cavities. The novel structure doubles the number of coupled laser emitters and the output power. Eight 800-nm diode laser bars were coupled and combined with polarization multiplexing, achieving a continuous wavelength power of 212 W, a broad spectrum of 19.1 nm, an M2 (times diffraction limited factor) beam quality of 2.2×16.7 and a brightness of 236MW/cm2/sr. [ABSTRACT FROM AUTHOR]