High-power diode-pumped continuous-wave Nd(3+) lasers at wavelengths near 1.44 microm

We demonstrate longitudinally diode-pumped operation of Nd:YAG and Nd:YAP lasers at the long-wavelength end of the (4)F(3/2) ? (4)I(13/2) transition in the eye-safe spectral region at 1444 and 1430 nm, respectively. Special crystal coatings were required for achievement of lasing at these wavelengths. Output powers of up to 4.9 and 2.2 W, with slope efficiencies of up to 22% and 8%, respectively, were achieved. Polarized operation of the Nd:YAG laser yielded output powers of 76% as compared with unpolarized operation. Because of thermal stress, both YAG and YAP crystals were fractured at roughly 25 W of absorbed longitudinal pump power.     

Diode-end-Pumped Nd:YAG Ceramic and Crystal Operation at 1,123 nm

We present a high-power diode-end-pumped continuous-wave Nd:YAG laser operating at 1,123 nm. Laser operation was carried out and compared using high optical quality Nd:YAG ceramics fabricated in-house and commercial Nd:YAG single crystals. At the absorbed diode pump powers of 23.2 and 28.0 W, output powers of 10.7 and 12.5 W at 1,123 nm were achieved for the employed ceramics and crystals as the laser material, which correspond to conversion efficiencies of 46.1% and 44.6%. For high-power lasers, the Nd:YAG ceramic has the advantage of a higher destructive threshold than that of commercial crystals.     

Single rod efficient Nd:YAG and Nd:YALO lasers with average output powers of 46 and 47 W in diffraction limited beams with M<1.2 and 100 W with M<3.7

Using a new resonator concept guaranteeing fundamental mode operation, flashlamp pumped Nd lasers with average output powers of 46 and 47 W for the two materials were realized with beam qualities better than 1.2*DL. Due to the absence of thermally induced birefringence the efficiency of the Nd:YALO laser was up to 1.85% and thus 1.5 times higher than that of the realized Nd:YAG laser. The Nd:YALO laser output is linear polarized. Average output power of 100 W could be extracted from a Nd:YAG single rod oscillator with a beam quality of better than 3.7×DL.     

Compact corner-pumped Nd:YAG/YAG composite slab laser

Corner-pumping is a new pumping scheme in diode-pumped all-solid-state lasers, having such advantages as high pump efficiency, favorable pump uniformity and low cost. Compact corner-pumped Nd:YAG/YAG composite slab lasers at 1064 nm with low or medium output powers and high efficiency are demonstrated in this paper. Combined with intracavity frequency doubling by a LBO crystal, a corner-pumped Nd:YAG/YAG composite slab 532 nm green laser with a stable output is realized successfully. The experimental results show that corner-pumping can reduce laser costs greatly, release the thermal effects of slab crystals and improve the output beam quality, and that the new pumping scheme is feasible in the design of diode-pumped all-solid-state lasers with low or medium output powers.     

Longitudinally diode-pumped Nd:YAG double-clad planar waveguide laser

We report the demonstration of a near-diffraction-limited, compact, diode-end-pumped double-clad planar waveguide Nd:YAG laser. Efficient laser operation was achieved for the three dominant Nd(3+) transitions, at 1.064, 0.946, and 1.32microm , with TE polarized output powers of 1.33, 0.57, and 0.33 W for the available output couplers. The output beam from the monolithic plane-plane laser cavity had measured M(2) values of 1.0 and 1.8 perpendicular and parallel, respectively, to the plane of the waveguide.     

A simple approach to designation of the intracavity resonator for second harmonic Nd:YAG laser

In this paper, the rate equation models, which have been used for describing the high repetitive Q-switched intracavity doubling of Nd:YAG laser, are represented. According to these models and onthe basis of resonator length as the most important parameter for designation of the laser system, a computational procedure (block diagram), which is applied for determination of the doubling intracavity resonator specifications of the Nd:YAG laser, has been provided. According to the resonator length the beam quality inside the resonator for second harmonic generation of Nd:YAG laser in different output powers has been calculated. The results for several green output powers of the laser are compared with the experimental data, and good agreement is obtained.     

Simple picosecond dye laser system pumped by a frequency doubled,optically compressed Q-switched mode-locked Nd:YAG laser

Using the frequency doubled output of the 3 ps pulses from a temporally compressed cw Q-switched and mode-locked Nd:YAG laser, a simple synchronously pumped dye laser was constructed to give frequency tunable operation with short pulses in the 5–10 ps range and peak powers of ～ 15 kW. A circularly scanning streak camera operating in stroboscopic mode was also used to examine pulse formation in the dye laser.     

Lasers for materials processing: specifications and trends

An overview is given of the types of lasers dominating the field of laser materials processing. The most prominent lasers in this field are the CO₂ and the Nd: YAG laser. The domain of CO₂ lasers is applications which demand high laser powers (up to 30 kW are available at present), whereas the domain of Nd:YAG lasers is micro-machining applications. In the kilowatt range of laser output power, the two types of lasers are in competition. New diffusion-cooled CO₂ laser systems are capable of output laser powers of several kilowatts, with good beam qualities, while still being quite compact. The output power and beam quality of Nd:YAG lasers has been improved in recent years, so that Nd:YAG lasers are now an alternative to CO₂ lasers even in the kilowatt range. This is especially true for applications that demand optical fibre transmission of the laser beam, which is possible with Nd:YAG laser light but not with the longerwavelength light emitted by CO₂ lasers. The main problem in solid-state lasers such as Nd:YAG is the thermal lensing effect and damage due to thermal stresses. In order to reduce thermal loading, cooling has to be enhanced. Several alternative geometries have been proposed to reduce thermal loading and, by this, thermal lensing effects. There are now slab and tube geometries which allow much higher output powers than the conventionally used laser rods. A very new scheme proposes a thin slab whose cooled side is also used as one of the laser mirrors, so that thermal gradients occur mainly in the direction of the beam propagation and not perpendicular to it, as is the case in the other geometries. As well as CO₂ and Nd:YAG lasers, semiconductor laser diodes are very promising for direct use of the emitted light or as pump sources for Nd:YAG and other solid-state lasers. When packaging together thousands of single laser diodes, output powers of several kilowatts can be realized. Major problems are collimation of the highly divergent laser beams and cooling of the laser diode bars.     

High power laser operation with crystal fibers

We present the very last results on the development of high-power lasers with crystal fibers in Nd:YAG and in Yb:YAG grown by the Micro-Pulling Down technique. An overview of the main optical properties of the grown crystal fibers is given as well as the principles of the diode-pumped systems are developed. The average output power obtained with those materials reaches now several tens of watts in the CW regime and in high repetition rate Q-switched operation. Pulses with an energy of several millijoules have been obtained with pulse durations from 10 to 20 ns and peak powers from 100 kW to 350 kW. In each case, the measured M ² quality factors remained in the range 2.5 to 5. In addition, the first demonstration of high-power laser emission with an Yb:YAG crystal fiber of 0.4 mm in diameter is reported. In this case, we obtained an output power of 27 W at 1030 nm under 100 W of pump power at 940 nm in CW regime. To our knowledge, those results represent the highest powers ever generated with crystal fibers obtained directly from the growth. We finally conclude this work by exposing the potential of crystal fiber lasers for a new generation of high-power laser systems.     

Continuous-wave green laser of 34 W by intracavity frequency doubling in diode-side-pumped Nd:YAG/KTP

Continuous-wave green laser with a maximum power of 34 W has been obtained by intracavity frequency doubling with KTP in diode-side-pumped Nd：YAG. The Nd：YAG/KTP green laser has a simple three- mirror V-fold cavity structure. The optical-to-optical conversion efficiency is 9.5%. The instability of the laser is measured when the output powers are near 16, 21, 30, and 34 W after the beam is filtered. At the maximum output power, the M^2 factor is measured to be 8.     

200兆赫高功率CW锁模YAG激光泵浦源研究

本文报导一台200MHz 12W平均功率的CW锁模Nd:YAG激光泵浦源,输出脉宽约100ps,能够可靠地长期稳定运转。     

Highly efficient in-band pumped Er:YAG laser with 60 W of output at 1645 nm

A high-power Er:YAG laser that is in-band pumped by a high-power cladding-pumped erbium-ytterbium codoped fiber laser operating at 1532 nm is reported. The Er:YAG laser produced 60.3 W of continuous-wave output at 1645.3 nm in a beam with M2 approximately equal to 3 for 82 W of incident pump power and 20 W of TEM00 output with M2 < 1.2 for 32.4 W of incident pump power. The slope efficiency with respect to incident pump power at pump powers of >20 W was approximately 81%. In the Q-switched mode of operation, a slightly modified resonator configuration incorporating an electro-optic Q switch produced pulses of approximately 4 mJ energy and approximately 100 ns (FWHM) duration, corresponding to a peak power of approximately 42 kW at a repetition rate of 1 kHz for an incident pump power of 16.8 W. The prospects for further improvement in continuous-wave and Q-switched performance are discussed.     

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.     

Green-Beam Generation of 40W by Use of an Intracavity Frequency-Doubled Diode Side-Pumped Nd:YAG Laser

A cw diode side-pumped Nd：YAO laser is frequency doubled to 532nm with an intracavity KTP crystal in a Vshaped arrangement, achieving an output power of 40 W corresponding to an optical-optical conversion efficiency of 9.7%. The instabilities and the M2-parameters of the laser are measured at different output powers after the beam is filtered.     

Continuous-wave operation and Q-switched mode locking of Cr(4+):YAG microchip lasers

Cw-operation, gain-switched, and passively Q -switched mode locking of Cr(4+): YAG microchip lasers with output powers of several hundred milliwatts is demonstrated experimentally in the eye-safe region near 1.5microm . Requirements for cw mode locking of such lasers are investigated by numerical simulations.     

High average power,all-solid-state external resonator Raman laser

As much as 3 W of average power at 1064 nm from a diode-pumped Nd:YAG laser, Q switched at 4 kHz, was used to pump an external-resonator, crystalline Ba(NO3)2 Raman laser generating a maximum of 1.3-W output at the first Stokes wavelength of 1197 nm. The slope efficiency was 63% with respect to the fundamental power incident on the Ba(NO3)2 crystal. A reduction in the beam quality of the Stokes output from M2 approximately 1.4 at lower Stokes powers to M2 approximately 3.4 at higher powers is attributed to thermal loading of the Raman-active crystal.     

Powerful solid-state transversely diode-pumped YAG: Nd lasers with improved radiation quality

YAG: Nd lasers with transverse diode pumping of a cylindrical active (lasing) element are developed and studied. Pumping is carried out with continuous-wave (cw) laser diode array modules. At pump powers of 500, 820, and 1400 W, the output powers of the lasers operating in the multimodal regime are, respectively, 150, 350, and 500 W. The optical efficiency exceeds 30%. In the case of an unstable resonator operating in the negative branch of the stability diagram, the laser power equals 320 W with a beam divergence only twice as large as the diffraction limit. The design of a YAG: Nd laser pumped with pulsed-periodic laser diode array modules is presented. The total pump energy is 5 J, and the width and repetition rate of pulses are, respectively, 250 μs and 100 Hz.     

Efficient corner-pumped Nd:YAG/YAG composite slab laser

A corner-pumped type is a new pumping type in the diode-pumped all-solid-state lasers, which has the advantages of high pump efficiency and favourable pump uniformity. A highly efficient corner-pumped Nd:YAG/YAG composite slab laser is demonstrated in this paper. The maximal continuous-wave output power of the 1064~nm laser is up to 18.57~W with a slope efficiency and an optical-to-optical conversion efficiency of 44.9{\%} and 39.8{\%}, respectively. Inserting an acousto-optic $Q$-switch in the cavity, the highest average output power of the quasi-continuous wave 1064~nm laser of 6.73~W is obtained at a repetition rate of 9.26~kHz. The experimental results show that a corner-pumped type is a kind of feasible schedules in the design of diode-pumped all-solid-state lasers with low or medium output powers.     

Positive-branch unstable resonators with thermal lens compensation

In order to compensate for thermal lensing in Nd : YAG rod active media, placed in unstable resonators with a super-Gaussian reflectivity profile of the output mirror, a deformable thin glass plate was used as the rear mirror. Unstable resonators with a magnification of M = 1.8 and with one and two Nd : YAG rods inside were investigated. By a proper variation of the radius of the thin glass plate, the magnification of the resonator was maintained constant by varying the refractive powers of the rods. For compensated resonators, the output energy of the laser working at 10 Hz repetition rate and pump energies up to 50 J per pulse was close to those obtained for a 1 Hz repetition rate.     

Power scaling of blue and red light based on frequency mixing inside adhesive-free bond composite Nd:YAG laser cavity

We report our results on effective third-harmonic generation (THG) by cascading quasi-phase-matched second-harmonic and sum-frequency generation in a dual-period-periodically-poled KTP crystal. Significant improvement of the output powers were achieved for the 440 nm blue light and 660 nm red light based on Q-switched frequency-tripling and frequency-doubling 1319-nm radiation inside an adhesive-free bond composite Nd:YAG laser. The highest output powers of 197 mW and 1.19 W were achieved for the blue and red light at the corresponding input powers of 12.9 and 17.1 W for the diode laser.