CW Laser Output Research Articles

Demonstration and CW laser performances of composite YAG/Nd:LuAG/YAG transparent laser ceramic

Composite YAG/Nd:LuAG/YAG transparent ceramics with sandwich structure were fabricated by a non-aqueous tape casting method and vacuum solid-state sintering technology. The cations' (Y3+, Lu3+, Nd3+) diffusion behaviors across the contact interfaces between the pure YAG and Nd3+-doped LuAG layers were determined by Fick's second law. The refractive indices for various wavelengths were determined by fitting with an equation derived from Sellmeier's dispersion equation. Finally, CW laser performances under 808 nm diode-laser pumping were studied with two different ways of pumping, namely the perpendicularly and longitudinally pumping methods. For perpendicular pumping, the variation of CW laser output power with incident pump power was investigated, for which a maximum output power of 1.13 W was observed, whereas in the case of longitudinal pumping, the CW laser output power increased linearly with incident pump power and the opt-to-opt efficiency was estimated to be 0.4%.

Lasing and thermal characteristics of Yb:YAG/YAG composite with atomic diffusion bonding

We demonstrated the laser performance of an Yb:YAG/YAG composite ceramic laser medium mounted on an aluminium heatsink via atomic diffusion bonding (ADB) technique using nanocrystalline metal films at room temperature in air. The surface temperature rise of the ADB bonded laser medium was linear with 57 °C lower than that of the commercially available soldered Yb:YAG thin disk at the pump power of 280 W. Moreover, the ADB disk was pumped 1.5 times higher (7.3 kW cm−2) than the typical damage threshold of the soldered disk without any sign of damage. The undoped capping may be effective for the suppression of ASE heating; however, according to the in situ OPD measurement it induces strong thermal lensing. The CW laser output power of 177 W was obtained at the pump power of 450 W with the optical-to-optical efficiency of 40% using V-shape cavity.

Research on all-solid-state blue lasers

Blue lasers have many important applications such as high-density optical data storage, biological and medical diagnostics, color displays, and submarine laser imaging and communication. High efficiency, high brightness and compactness all-solid-state blue lasers have attracted much attention for their merits. In this paper, four main ways for achieving all-solid-state blue lasers are reviewed and compared in detail, such as the semiconductor laser, the frequency-doubling of the semiconductor laser, the up-conversion blue laser, the nonlinear optical frequency conversion of Nd3+-doped or optical parametric oscillating lasers and so on. Results show that the nonlinear optical frequency conversion of the Nd3+-doped lasers is a potential way to realize a high power, high efficiency cw or pulsed blue laser output.

Development of solar concentrators for high-power solar-pumped lasers.

We have developed unique solar concentrators for solar-pumped solid-state lasers to improve both efficiency and laser output power. Natural sunlight is collected by a primary concentrator which is a 2 m×2 m Fresnel lens, and confined by a cone-shaped hybrid concentrator. Such solar power is coupled to a laser rod by a cylinder with coolant surrounding it that is called a liquid light-guide lens (LLGL). Performance of the cylindrical LLGL has been characterized analytically and experimentally. Since a 14 mm diameter LLGL generates efficient and uniform pumping along a Nd:YAG rod that is 6 mm in diameter and 100 mm in length, 120 W cw laser output is achieved with beam quality factor M2 of 137 and overall slope efficiency of 4.3%. The collection efficiency is 30.0 W/m2, which is 1.5 times larger than the previous record. The overall conversion efficiency is more than 3.2%, which can be comparable to a commercial lamp-pumped solid-state laser. The concept of the light-guide lens can be applied for concentrator photovoltaics or other solar energy optics.

Nd:MgO:LiTaO3 crystal for self-doubling laser applications: growth, structure, thermal and laser properties

Nd3+ and Mg2+ co-doped LiTaO3 (Nd:MgO:LT) crystal has great potential for applications in self-frequency doubling (SFD) lasers, and self-optical parametric oscillation (SOPO) infrared lasers. However, a related high performance laser device has not yet been realized. No reliable data on the basic physical properties of Nd:MgO:LT have been obtained, because of the lack of high quality Nd:MgO:LT crystals available due to the great difficulty in growing this crystal. In this paper, by optimizing the growth parameters and the thermal field by means of simulation, a high quality Nd3+ and Mg2+ co-doped LiTaO3 crystal was grown by a modified Czochralski method. A comprehensive characterization of the crystal, including structure, composition, thermal properties, and CW laser performance, was performed. The experimental results indicate that Nd:MgO:LT is a monocrystal with strong anisotropic physical properties. The anisotropic thermal expansion was confirmed by observing the lattice parameter variation via temperature-dependent XRD analysis. Some important physical property data, such as thermal diffusivity, thermal conductivity and specific heat of the Nd:MgO:LT single crystal are reported for the first time, and should be of great utility for the application of this crystal. A CW laser output power of 3.58 W with an optical-to-optical conversion efficiency of 11.55, and a slope efficiency of 13.78%, was achieved with an incident pump power of 31 W, which is the highest laser output reported for this kind of crystal. It is demonstrated that single crystal Nd:MgO:LT will have important applications in SFD and SOPO lasers.

Continuous-wave diode-pumped laser action of Nd^3+-doped photo-thermo-refractive glass

Laser action of the photo-thermo-refractive (PTR) glass, which is the photosensitive material for holographic recording of volume Bragg gratings (VBGs), was demonstrated for the first time by introducing Nd³⁺. Nd:PTR glass has a bandwidth of 27.8 nm and 16.0 nm for luminescence and absorption, respectively. An uncoated 2 mm thick Nd:PTR element generated cw laser output of 124 mW, with a slope efficiency of 25%, by laser diode pumping. This Nd:PTR glass also performed wide bandwidth laser action at 1053.9-1063.3 nm, where the decrease of the pump-absorption efficiency was held off below 30%, even under a 3.5 nm shift of pump wavelength from its absorption center.

High power composite Nd:YAG/YAG zigzag dual-slab laser oscillator

We report a high power zigzag slab laser oscillator employing two composite Nd:YAG/YAG slab in the cavity. The CW laser output with the power of 401 W was achieved from the oscillator with the optical-optical efficiency of 32.6%. The beam quality is estimated as M x 2 ≈ 10, M y 2 ∼ 50 in the slab width and thickness direction, respectively.

CW and Q-switched laser output of LD-end-pumped 1.06μm c-cut Nd:LuVO_4laser

The continuous-wave (cw) and pulsed laser performances of laser-diode (LD)-end-pumped c-cut Nd:LuVO(4) at 1.06 mum were achieved for the first time. Maximum cw output of 2.35W was obtained. Compared with the cw laser output of a-cut Nd:LuVO(4) crystal, the efficient emission cross-section of the c-cut crystal has been calculated to be 3.24x10(-19)cm(2). The largest pulse repetition rate, shortest pulse width, largest pulse energy and highest peak power were measured to be 20 kHz, 12 ns, 84.93 muJ and 7.02 kW, respectively, by using Cr(4+):YAG crystals as the saturable absorbers in the passive pulsed laser output experiments.

Experimental 511 W Composite Nd:YAG Ceramic Laser

We demonstrate a 511 W laser diode pumped compositeNd:YAG ceramic laser. The optical pumping system is consisted of fivelaser diode stacked arrays arranged in a pentagonal shape around theceramic rod whose size is Φ6.35×144 mm. When the pumping power is1600 W, the cw laser output up to 511 W at 1064 nm can be obtained with alinear plano–plano cavity, and the optical-to-optical efficiency is31.9%. To our knowledge, this is the highest value of laser output byusing a newly invented composite Nd:YAG ceramic rod as the gain medium.

Tunable Q-switched/cavity-dumped Z-fold CO/sub 2/ waveguide laser with two channels and common electrodes

A tunable Q-switched/cavity-dumped z-fold CO/sub 2/ waveguide laser with two channels and common electrodes is studied. The Q-switched and cavity-dumped pulse lasers have been obtained from the z-fold channel with the tunable pulse repetition frequency (PRF) of 1-70 kHz. At the Q-switched operation, the peak power is 730 W and the pulsewidth is 150 ns at the PRF of 10 KHz. At the cavity-dumped operation, the pulse laser width can be adjusted. The peak power is 6000 W with the pulsewidth of 20 ns and 3400 W for 32 ns. CW laser output has been obtained from the other channel and its frequency can be tuned by a piezoelectric transducer. The Q-switched and cavity-dumped pulse laser heterodyne waveforms are observed.

Tunable electro-optically <bold>Q</bold>-switched rf excited partial <bold>Z</bold>-fold <inline-formula><math display="inline" overflow="scroll"><msub><mi>CO</mi><mrow><mn>2</mn></mrow></msub></math></inline-formula> waveguide laser with two channels

A tunable electro-optically Q-switched rf-excited partial Z-fold CO 2 waveguide laser with two channels has been designed. Q-switched pulses were obtained from the partial Z-fold channel. The peak power is 730 W, and the pulse width is 150 ns. Cw laser output was obtained from the other channel, which can be tuned by a grating. A stable pulse heterodyne waveform and its Fourier transform (frequency spectrum) were also observed.

5.5 W CW Yb3+:Y2O3 ceramic laser pumped with 970 nm laser diode

CW laser output has been demonstrated for polycrystalline transparent 10 at.% Yb3+-doped Y2O3 ceramics. End-pumped with 970 nm laser diode, a maximum output power of 5.5 W has been obtained with absorbed pump power of 31.1 W. The slope efficiency is 25% while the threshold pump power is 5.6 W. Saturation is not observed in our experiments, indicating higher laser output can be expected with higher pump power.

Jet-type, water-cooled heat sink that yields 255-W continuous-wave laser output at 808 nm from a 1-cm laser diode bar

A newly designed jet-type, water-cooled heat sink (the funryu heat sink, meaning fountain flow in Japanese) yielded 255-W cw laser output at 808 nm from a 1-cm bar made from InGaAsP/InGaP quantum-well active layers with a 67% fill factor [70 quantum-well laser diode (LD) array along the 1-cm bar]. A funryu heat sink measuring 1.1 mm in thickness gave the LD 0.25 degrees C/W thermal resistance, one of the lowest values achieved with a 1-cm LD bar. Over a short period of operation, the device reached a maximum cw power of 255 W. To the best of our knowledge, this is the highest power ever achieved in 808-nm LD operation. In the future, the funryu heat sink may be capable of 80-W cw operation over an extended lifetime of several thousand hours.

Diode-pumped Yb:Y2O3 ceramic laser

We report on a diode-pumped polycrystalline Yb:Y2O3 ceramic laser. We demonstrate that, with a pump power of 11 W at 937 nm, 0.75-W cw laser output at 1078 nm can be obtained from the laser. The laser had a threshold of 4.7 W and a slope efficiency of 12.6% when an output coupler of R=98% was used.

High-power continuous-wave diode-pumped Nd:YAlO_3 laser that emits on low-gain 1378- and 1385-nm transitions

Efficient operation of a diode-pumped Nd:YAlO(3) laser on low-gain 1378- and 1385-nm transitions is reported for the first time, to our knowledge. A three-mirror folded cavity with a prism yielded a cw laser output power of 800 mW for an absorbed pump power of 11 W. The laser beam was TEM(00). We managed to eliminate the instabilities in the output power by purging the cavity of water vapor with nitrogen.

72 W Nd:Y3Al5O12 ceramic laser

A high-power continuous-wave polycrystalline 1% Nd:Y3Al5O12 (Nd:YAG) ceramic rod laser was demonstrated. With 290 W/808 nm laser diode pumping, cw laser output of 72 W was obtained at 1064 nm. The optical-to-optical conversion efficiency is 24.8%. Thermally induced birefringence properties of Nd:YAG ceramic was also investigated.

Tunable electrooptically Q-switched RF excited CO 2 waveguide laser with two channels

A tunable electrooptically Q-switched RF excited waveguide CO 2 laser with two channels is presented. Q-switched pulses have been obtained from one of the channels. The peak power is 300 W and the pulse width is 140 ns. CW laser output has been obtained from the other channel, which can been tuned by a PZT. The short-term heterodyne stability can be up to 10 −9.

Influence of pore volume on laser performance of Nd : YAG ceramics

For present study, 1.1 at % Nd-doped YAG ceramics with a controlled pore volume (150–930 vol ppm) were fabricated by a solid-state reaction method using high-purity powders. The scattering coefficients of Nd : YAG ceramics, obtained from Fresnel' equation, increased simply with increases in the pore volume. The cw laser output power of Nd : YAG ceramics was clearly related to the scattering coefficients of the specimens examined in the present works, which in turn were affected on the pore volume. The effective scattering coefficients of Nd : YAG ceramics with a pore volume of ∼150 vol ppm were nearly equivalent to those of a 0.9 at %Nd : YAG single crystal by Czochralski method. As the exciting power was increased under excitation by an 808-nm diode laser, however, the laser output power of the Nd : YAG ceramics exceeded that of the Nd : YAG single crystal because of the fairly large amount of Nd additives. The lasing performance of the Nd : YAG ceramics changed drastically with change in pore volume. On the other hand, lasing performance was not affected by the existence of grain boundaries in the polycrystalline Nd : YAG ceramics.

New green self-frequency-doubling diode-pumped Nd:Ca 4 GdO(BO 3 ) 3 laser

:Ca4GdO(BO3)3 (Nd:GdCOB). 21 mW of green cw laser emission for an absorbed pump power of 820 mW were achieved under laser diode-pumping. 64 mW of green cw laser output were obtained with 1 W of absorbed pump power under titanium-sapphire pumping. Its availability in large-size crystals with good optical quality makes Nd:GdCOB a true challenger to the best SFD laser crystal reported so far: Nd:YAl3(BO3)4 (Nd:YAB or NYAB).

Gain optimization of a Kerr-lens mode-locked Cr:forsterite laser in the CW regime: theory and experiments

We present a parametric study of the optimisation of a longitudinally pumped astigmatically-compensated Cr 4+:forsterite laser and compare with experimental results. The gain medium is characterized by a low figure of merit and an upper state life time which is sensitive to temperature, and therefore to pump power. The objective is the optimisation in the CW regime in order to get the highest circulating intensity, thereby making self mode-locking easier. We solve the rate equations of a two-level vibronic laser to obtain the CW laser output and show that there exits an optimum crystal length, weakly dependent on pump power, output coupler and upper state life time. The model is shown to agree well with experiment when the pump power-induced thermal effects are taken into account.