Tri-wavelength laser with Nd:CLTGG crystal

Continuous-wave (CW) and passively Q-switched operations of laser diode-end-pumped Nd:CLTGG laser at 1.06 μm was demonstrated for the first time. The laser spectrum was found to be tri-wavelength, with respective wavelengths of 1058.4, 1060.5, and 1065.5 nm for both CW and passive Q-switching regime. The highest CW output power of 2.6 W was obtained with an optical-optical conversion efficiency of 13.9% and a slope efficiency of 17.1%. In the passive Q-switching regime, the highest output power, shortest pulse width, largest pulse energy and highest peak power were achieved as 242 mW, 45.8 ns, 1.65 μJ and 0.4 kW, respectively. The passively Q-switched tri-wavelength laser should have the potential to be used for terahertz radiation generation.     

60 W yellow laser at 561 nm by intracavity frequency doubling of a diode-pumped Q-switched Nd:YAG laser

A high-power yellow laser was achieved by intracavity frequency doubling of a diode-pumped Nd:YAG rod laser. A solid etalon was inserted into the resonator to implement efficient operation of the low-gain single line at 1123 nm transition. By using a LBO crystal inside the cavity as the frequency doubler, the maximum output power of the 561 nm yellow laser was obtained to be as high as 60.3 W with a pulse repetition frequency of 6 kHz, corresponding to an optical-to-optical conversion efficiency of about 6.1%. The output power fluctuation of the yellow laser was measured to be better than 3% in half an hour.     

Performance of actively Q-switched Nd:LiLuF<Subscript>4</Subscript> crystal end-pumped by a 792 nm laser diode

An efficient laser diode end-pumped continuous-wave (CW) and AO Q-switched laser of Nd:LiLuF₄ crystal with dual central wavelengths of 1053.1 and 1054.7 nm is reported for the first time. The maximum CW output power of 6.22 W was obtained at absorbed pump power of ∼14.6 W with the output transmission of 2%. The optical conversion efficiency is ∼43%, corresponding to a slope efficiency of about 48% with respect to the absorbed pump. For the Q-switched operation, the shortest pulse width of 17 ns was obtained at the pulse repetition frequency (PRF) of 0.5 kHz, resulting in a pulse energy of 2.24 mJ and peak power of 131.8 kW.     

Efficient diode-pumped passively Q-switched laser with Nd:YAG/Cr:YAG composite crystal

Diffusion bonded Nd:YAG/Cr:YAG composite laser crystal has been employed to perform a compact diode-pumped passively Q-switched laser. At the incident pump power of 3.3 W and pulse repetition rate of 16.3 kHz, the maximum average output of 592 mW has been obtained, corresponding to an optical-to-optical conversion efficiency of 18%. Stable passively Q-switched operation with peak power of 6.5 kW and pulse duration of 6 ns was also achieved. It has been experimentally revealed that Nd:host/Cr:YAG composite structure is a promising material for compact cost-effective Q-switched laser sources with high-peak power and short pulse duration. In addition, thermal lens effect (TLE) in the active medium and its impact on the Q-switched laser performance have been analyzed.     

Performance improvement of high repetition rate electro-optical cavity-dumped Nd:GdVO<Subscript>4</Subscript> laser

We improved the electro-optical cavity-dumped Nd:GdVO₄ laser performance at high repetition rates by employing continuous-grown GdVO₄/Nd:GdVO₄ composite crystal under 879 nm diode-laser pumping. A constant 3.8 ns duration pulsed laser was obtained and the repetition rate could reach up to 100 kHz with a maximum average output power of 13.1 W and a slope efficiency of 56.4%, corresponding to a peak power of 34.4 kW.     

Highly efficient diode side-pumped Nd:YAG ceramic laser with 210 W output power

We developed a highly efficient diode side-pumped Nd:YAG ceramic laser with a diffusive reflector as an optical pump cavity. A maximum output power of 211.6 W was obtained with an optical-to-optical conversion efficiency of 48.7%. This corresponds to the highest conversion efficiency in the side-pumped ceramic rod. Thermal effects of the Nd:YAG ceramic rod were analyzed in detail through the measurements of laser output powers and beam profiles near the critically unstable region. A M² beam quality factor of 18.7 was obtained at the maximum laser output power.     

Efficient diode-pumped Nd:GGG laser operation at 933.6 and 937.3 nm

CW laser emission on the quasi 3-level (⁴F_3/2→⁴I_9/2) transition in Nd:GGG is reported for different pump focusing and resonator dimensions. A nearly hemispherical plano-concave resonator led at 937.3 nm to a maximum output power of 4.1 W for an incident pump power of 21.7 W, thus corresponding to a slope efficiency of about 23.5%. Laser operation was also obtained for the first time around 933.6 nm by using a glass etalon for frequency selection with a maximum output power of 2.3 W and a slope efficiency of 16% with respect to the incident pump power. Dual-wavelength operation (around 933.6 and 937.3 nm), which offers a potential source to generate THz radiation, is also reported.     

Compact resonantly intra-cavity pumped tunable Ho:Sc2SiO5 laser

A compact intra-cavity pumped low threshold continuous-wave Ho:Sc₂SiO₅ laser is reported. The characteristics of output wavelength tuning are investigated by use a intra-cavity briefringent (BF) filter. A wavelength tunable range of 140 nm from 2020 to 2160 nm is achieved. For the free-running mode, the laser slope efficiency is 24.8%, when the output central wavelength is 2110 nm. The laser threshold is about 820 mW of incident pump power. With the BF filter, a maximum output power of 870 mW is obtained at the incident pump power of 5 W, corresponding to a slope efficiency of 20.3%. The characteristics of output wavelength verse the crystal temperature are also investigated.     

Optimal design for a diode-pumped high-power high-efficiency high-beam-quality laser

We have demonstrated and analyzed a high-power high-efficiency high-beam-quality continuous-wave (cw) Yb:YAG laser, which is directly pumped into the upper lasing level by a fiber-coupled laser diode with a center wavelength of 969 nm. To achieve high efficiency and high beam quality simultaneously, we carried out a series of comparing experiments by changing the laser-medium length and pump-beam waist radius. From the cw Yb:YAG laser with a 5.0-at.%-Yb³⁺-doped and 5-mm-long crystal, an output power of 19.0 W has been obtained for a pump-beam waist radius of 138 μm. The maximum slope efficiency and optical-to-optical conversion efficiency are 78.9% and 55.3%, respectively. The M² factors of the laser beam are 1.33 in the vertical direction and 1.82 in the horizontal direction.     

Efficient double-clad Yb3+-doped silica fibre laser pumped by an unfocused diode laser

A moderate output power Yb³⁺-doped double-clad fibre laser pumped by an unfocused diode laser is reported. This pumping configuration omits micro positioned lenses used in fibre coupled laser diodes, thus making the system significantly less complex and more robust. The maximum launch efficiency was ～80% and the maximum output power was >5 W with a measured FWHM of 18 pm.     

A tunable and single-longitudinal-mode Ho:YLF laser

A 1.94 μm Tm-doped fiber laser pumped tunable single-longitudinal-mode Ho:YLF laser with double etalons was reported for the first time. The maximum single-longitudinal-mode output power of 345 mW at 2051.6 nm was achieved at the absorbed pump power of 11.9 W, corresponding to a slope efficiency of 5.5% and an optical conversion efficiency of 2.9%. By regulating the angle of the F–P etalons, the output wavelength of the laser can be tuned from 2051.6 nm to 2063.3 nm. The single-longitude-mode Ho:YLF laser operating at 2 μm can be used as the seed laser source of coherent Doppler lidar, differential absorption lidar and so on.     

Efficient GTR-KTP IOPO driven by a diode-pumped Nd:YAG/Cr4+:YAG laser with the shared cavity configuration

An efficient eye-safe GTR-KTP IOPO with the shared cavity configuration and excited by a diode-end-pumped composite Nd:YAG/Cr⁴⁺:YAG laser was demonstrated. Under the incident LD power of 8.4 W, the maximum average output power of 900 mW at 1572 nm was obtained with the T=33% output coupler, corresponding to a diode-to-signal conversion efficiency of 10.7%. The corresponding signal pulse width and repetition rate were respectively 2.2 ns and 12 kHz, with the peak power and single pulse energy estimated to be 34.1 kW and 75 μJ, respectively. The instability of the average signal output power over hours-long operation was found to be 2.0%. As for the common KTP IOPO at the same pump condition and cavity design, a lower average output power of 640 mW with a longer pulse width of 4.6 ns was obtained. The corresponding diode-to-signal conversion efficiency was reduced by 28.8% compared with that obtained in GTR-KTP IOPO. A theoretical model for the compact GTR-KTP IOPO was also presented in this paper. Theoretical analysis on the pulse characteristics of the signal was performed, which showed a good agreement with that obtained experimentally.     

A compact continuous-wave green laser with line beam for laser projection

An efficient and compact continuous-wave green laser with line beam using LBO crystal was developed. The maximum output power was 6.5 W. The optical-to-optical conversion efficiency was as high as 31%. The compact size of the line beam green laser was 2 cm×5 cm×8.8 cm. Reliability and stability of the green laser were evaluated.     

High efficiency diode laser side-pumped Nd:YAG rod laser

High efficiency laser performance of 2 mm diameter and 20 mm long Nd:YAG crystal rod transversely pumped by laser diode array is presented. Using the directly side-coupled geometry enclosed by cylindrical pump cavity plated with gold, we obtained long pulse energy of 4.6 mJ corresponding to optical-to-optical slope efficiency of 37%. The complete solid-state Nd:YAG laser is described to be simple, compact and highly efficient. Q-switching of the laser is also reported.     

400 mW and 16.5% wavelength conversion efficiency at 488 nm using a diode laser and a PPLN crystal in single pass configuration

Continuous wave power of more than 400 mW at 488 nm has been generated by frequency doubling of 2.45 W at 976 nm obtained from a distributed Bragg reflector tapered diode laser. This results in a wavelength conversion efficiency of 16.5% and an electrical-to-optical efficiency of more than 4.5%. We used a 50 mm long periodically poled MgO:LiNbO₃ bulk crystal in single-pass configuration for the second harmonic generation. This is to the author’s knowledge the highest output power and the highest wavelength conversion efficiency at 488 nm generated by a monolithic semiconductor laser device in single pass configuration with a bulk crystal. A deviation from the quadratic dependency of the frequency doubling is explained by the decrease of the beam quality of the fundamental wave.     

Passively Q-switched,high peak power Nd:YAG laser pumped by QCW diode laser

A Nd:YAG laser passively Q-switched by a Cr:YAG showed a high single pulse energy of 53.0 mJ and 5.1 MW peak power. The laser was pumped by quasi-continuous-wave diode bars from single side. The Q-switched pulse had optical-to-optical efficiency of 12% and average temporal duration of 10.4 ns when Cr:YAG with initial transmission of 9.0% was used. Intense pumping as well as very low initial transmission of the saturable absorber gave very high peak power.     

High-efficiency mid-infrared laser from synchronous optical parametric oscillation and amplification based on a single MgO:PPLN crystal

This paper presents a specially designed optical parametric oscillator (OPO) which achieved high-efficiency mid-infrared laser of 2.83 μm. The cascaded nonlinear interactions of OPO and optical parametric amplifier (OPA) were simultaneously realized in a single MgO:PPLN crystal. The signal oscillation of 1.70 μm was used to pump a secondary parametric process that resulted in amplification of the idler laser of 2.83 μm. When the MgO:PPLN crystal with a grating period of 31.2 μm was pumped by a 1.064 μm laser and operated at 148°C, the quasi-phase-matching of both OPO and OPA could be simultaneously achieved. Average output power of 7.68 W at 2.83 μm was obtained for 25 W of pump at 7 kHz. The power conversion efficiency of 2.83 μm laser was 30.7%, which was evidently higher than common OPOs.     

Tunable single-longitudinal-mode operation of a sandwich-type YAG/Ho:YAG/YAG ceramic laser

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 M² factor was measured to be 1.23.     

Diode-pumped actively Q-switched Nd:GGG laser operating at 938 nm

The stimulated emission cross-section of Nd:GGG crystal in 938 nm transition was measured by the amplifier approach. It is 2.3×10^?20 cm². A quasi-continuous-wave diode pumped, actively Q-switched Nd:GGG laser operating at 938 nm was demonstrated. Pumped by laser diodes with 900 W peak power and 300 μs pulse duration, it generated 168 mJ energy in long pulse mode. The slope efficiency was 36%. Q-switched by a KD?P Pockels cell, 41 mJ output pulse energy was obtained. The pulse duration and peak power were 120 ns and 340 kW, respectively. The optical to optical efficiency was 7%.     

LD-pumped actively Q-switched Tm,Ho:YLF laser at room temperature

We have investigated acoustic-optical Q-switched Tm,Ho:YLF laser end-pumped by a laser-diode. At room temperature, a 2.067 μm wavelength pulsed output is realized. Average output power, single pulse energy and pulse-width are measured at different incident pump powers and pulse repetition frequencies. When the incident pump power is 2.8 W, a maximum average output power of 189 mW is obtained at the repetition frequency of 9 kHz, and this corresponds to an optical conversion efficiency of 6.8%. The maximum single pulse energy of 65μJ, the shortest pulse-width with full-width at half-maximum (FWHM) of 138 ns and the maximum peak power of 470 W are obtained at the pulse repetition frequency of 1 kHz.