High-repetition-rate, intracavity-pumped KTP OPO at 1572 nm

An efficient, eye-safe, high-repetition-rate, intracavity optical parametric oscillator (IOPO) inside an acousto-optically Q-switched Nd:YVO₄ laser end pumped by a 30-W fiber-coupled diode laser was demonstrated. The pumping, acousto-optically Q-switched Nd:YVO₄ laser gives 3-W average output power at 1064-nm wavelength at 40-kHz repetition rate. An additional separating mirror, x-cut KTP crystal and output coupler highly reflective at 1064-nm and partially transparent at 1572-nm wavelengths form a flat–flat IOPO resonator of 35-mm length. We have achieved 3-ns-duration pulses for 20-mm-long KTP and 4-ns-duration pulses for 30-mm-long KTP, respectively. More than 8-kW-peak-power pulses with an average power of 1.5 W at the signal wavelength for 40-kHz repetition rate were demonstrated. Due to the intracavity spatial cleaning effect, a near diffraction limited signal beam was achieved despite a relatively worse beam quality of the pumping beam. Conversion efficiencies of 50% with respect to Q-switched output at 1064-nm wavelength and 11% with respect to diode pump power were achieved. PACS 42.55.Xi; 42.60.Gd; 42.65.Yj     

High repetition rate CH4 laser

A 16-m CF₄ laser oscillator has operated at 1 kHz in a cooled static cell. Pump energies required from the low pressure, Q-switched, cw discharge CO₂ laser were as low as 60 J. The laser cavity employed a multiple-pass off-axis path resonator in a ring configuration. CF₄ laser power at 615 cm^–1 and a 1-kHz repetition rate exceeded 300 W.     

Experiment and modeling of a diode-pumped 1.3 μm Nd:YVO<Subscript>4</Subscript> laser passively Q-switched with PbS-doped glass

A diode-pumped 1.34 m Nd:YVO₄ laser passively Q-switched with PbS quantum dots doped glass is presented. An average output power of 24 mW with a Q-switching efficiency of 13% and a Q-switched pulse width of 15 ns was obtained. A four level spectroscopic model of a PbS quantum dots doped glass saturable absorber is applied to numerically simulate passively Q-switched Nd:YVO₄ laser operation. It has been shown that for the simulation of passive Q-switching of 1.3 m Nd:YVO₄ lasers with PbS doped glasses as the saturable absorbers, it is necessary to take into account intensity dependence of bleaching relaxation times. PACS 42.60.Gd; 42.55.Xi; 42.70.Hj     

A powerful diode-pumped laser source for micro-machining with ps pulses in the infrared, the visible and the ultraviolet

We report a ps diode-pumped Nd:YVO₄ laser system for micro-machining applications. The system consists of a passively mode-locked oscillator followed by a regenerative amplifier. It provides laser pulses at 1064 nm with a pulse duration of 10.2 ps, a repetition rate of 20 kHz and an average output power of 10.8 W. This average power corresponds to a pulse energy of 0.54 mJ. Second-harmonic generation in LBO and fourth-harmonic generation in BBO provide visible (532-nm) and ultraviolet (266-nm) radiation with pulse energies of 270 J and 75 J, respectively. Amplification in a diode-pumped single-pass Nd:YVO₄ amplifier increases the pulse energy of the fundamental 1064-nm laser pulses to 1 mJ. PACS 42.55.Xi; 42.60.Da; 42.65.Ky; 42.65.Re     

Power scale-up of the diode-pumped actively Q-switched Nd:YVO4 Raman laser with an undoped YVO4 crystal as a Raman shifter

With an undoped YVO₄ crystal as a Raman shifter, we substantially improved the reliability and the output performance of an actively Q-switched 1176-nm Nd:YVO₄ Raman laser. With an incident pump power of 18.7 W, the average power is greater than 2.6 W at 80 kHz. The pulse width of the pulse envelope is shorter then 5 ns with mode-locked modulation. With an incident pump power of 12.7 W, the pulse energy and peak power is higher than 43 μJ and 14 kW at 40 kHz. PACS 42.55.Ye; 42.55.Xi; 42.60.Gd     

Diode-pumped doubly Q-switched YVO4/Nd:YVO4 laser with BBO electric-optic Q-switch and Cr4+:YAG saturable absorber

In the experiment, we have demonstrated the performance of a laser-diode, end-pumped, doubly Q-switched YVO₄/Nd:YVO₄ laser with both a BBO electric-optic (EO) Q-switch and Cr⁴⁺:YAG saturable absorber. At a maximum incident pump power of 15 W and an EO Q-switch repetition rate of 8 kHz, the stable laser pulses with the pulse duration 5.28 ns, the single pulse energy 0.14 mJ, and the pulse peak power 26 kW are obtained. The experimental results show that the double Q-switched laser with EO and Cr⁴⁺:YAG can generate the shorter pulse and the higher peak power in comparison to singly Q-switched laser with EO.     

Diode-pumped cw and Q-switched Nd:GdVO4 laser operating at 1.34 μm

A diode-pumped 1.34 m Nd:GdVO₄ laser operating in cw and active Q-switching modes has been demonstrated. 4.15 W of cw output power was obtained at the highest attainable pump power of 12.3 W, resulting in an optical conversion efficiency of 33.7%, the slope efficiency was determined to be 37.6%. In Q-switching operation, a maximum average output power of 2.7 W was generated at pulse repetition frequency (PRF) of 50 kHz, with an optical conversion efficiency of 22% and a slope efficiency of 29.2%. The laser pulses with shortest duration, highest energy and peak power were achieved at PRF of 10 kHz, the parameters being 15 ns, 160 J, and 10.7 kW, respectively. By intracavity frequency-doubling with a type II phased-matched KTP crystal, 0.62 W average power at 0.67 m was produced at a PRF of 15 kHz, the resulting pulse energy, peak power, and pulse width being 41.3 J, 2.2 kW, and 19 ns, respectively. A group of analytical formulae, based on rate equations, are presented to evaluate the operational parameters of an actively Q-switched laser. Calculated results were found to be in close consistency with the experimental data.     

High-repetition-rate Nd:YVO4 slab laser with a 1-D top-hat output beam

A high-repetition-rate electro-optic Q-switched Nd:YVO₄ slab laser is demonstrated in this paper. The Nd:YVO₄ slab inside the compact resonator is end-pumped by a 2-bar laser diode stack. The output beam with one dimension (1-D) top-hat intensity distribution at both near field and far field is generated. Continuous wave (CW) output of 13 5 W is obtained under the total pump power of 50 W. At the repetition rate of 40 kHz, the energy per pulse is 0.32 mJ with its pulse width of 26.3 ns. At 20 kHz, we have achieved the maximum pulse energy of 0.56 mJ and 56 kW peak power with 10 ns pulse width.     

Power scaling of a continuous-wave and passively Q-switched Yb:KLu(WO<Subscript>4</Subscript>)<Subscript>2</Subscript> laser end-pumped by a high-power diode

The power scaling capacity of a diode end-pumped Yb:KLu(WO₄)₂ laser, operating in the continuous-wave (cw) and passively Q-switched regimes, has been investigated. A cw output power of 11.5 W was achieved with an optical-to-optical efficiency of 41% with respect to the incident pump power, while the slope efficiency amounts to 60%. The passively Q-switchedoperation yielded an average output power of 4.3 W at the fundamental wavelength of 1031.7 nm, and 1.15 W of Raman radiation at 1139.3 nm. The total slope efficiency for Q-switched operation was 40%. The highest pulse energy, duration, and peak power were 170 μJ, 2.2 ns, and 77.3 kW for the fundamental radiation, and 51 μJ, 2.3 ns, and 22.2 kW for the Raman radiation. PACS 42.55.Rz; 42.55.Xi; 42.55.Ye     

High repetition rate passively Q-switched diode-pumped Nd:YVO4 laser

We demonstrated an efficient and compact, diode-pumped passively Q-switched Nd:YVO₄ laser operation at 1.064 μm wavelength with high repetition rate, using Cr⁴⁺:YAG as saturable absorber, formed with a simple flat–flat resonator. The maximum CW output power of 4.05 W was obtained at the incident pump power of 8 W. For Q-switched operation, the maximum average output power was measured to be 1.4 W with the corresponding repetition rate of 200 kHz, the pulse width of 60 ns when the initial transmission of Cr⁴⁺:YAG crystal was 85%. The shortest pulse width of 12 ns, the largest pulse energy of 36 μJ and the highest peak power of 3 kW were obtained when the Cr⁴⁺:YAG crystal with an initial transmission of 60% was used.     

Studies of laser-induced cavitation and tissue ablation in saline using a fibre-delivered pulsed HF laser

We describe studies of the interaction of 400 ns duration, fibre delivered, multiline (2.6–3.0 m) HF-laser pulses with cornea and retina samples in saline. In this wavelength region water exhibits strong absorption (beam penetration depth 1.6 m) and laser heating leads to the creation of a hot, high pressure, vapour cavity (laser-induced cavitation) at the fibre tip. The dynamics of vapour cavity growth have been investigated experimentally using the laser shadowgraph technique and theoretically by employing an equivalent spherical cavity model for an incompressible liquid. Measurements of ablation rates and transient acoustic pressures for cornea ablation in saline, together with scanning electron microscope evaluation of irradiated samples are used to assess the damage range and mechanisms for this mid-IR laser in a strongly absorbing fluid.     

Analysis of laser-diode end-pumped intracavity frequency-doubled,passively Q-switched and mode-locked Nd:YVO<Subscript>4</Subscript> laser

Simultaneous Q-switching and mode locking in a laser-diode end-pumped intracavity frequency-doubled Nd:YVO₄/KTP green laser using a Cr⁴⁺:YAG saturable absorber with 81% initial transmission is experimentally demonstrated. At an incident pump power of 6 W, 300 mW of average green power was obtained, which is around four times higher than the cw green power obtained without the Cr⁴⁺:YAG crystal. The repetition rate of the mode-locked green pulses was 400 MHz and the individual mode-locked pulse width was measured to be 500 ps. The repetition rate of the Q-sw itched envelope of the mode-locked pulses was 15 kHz at 6 W of incident pump power. The energy of the mode-locked pulse at the peak of the Q-sw itched envelope was estimated to be 1 J and the peak power was estimated to be 2.4 kW. The measured width and the total energy of the Q-sw itched envelope of the mode-locked pulses was 47 ns and 21 J, respectively, at the maximum incident pump power. An analysis of the system by incorporating a nonlinear loss term due to the intracavity second-harmonic generation to the general recurrence relation for the mode-locked pulses under the Q-sw itched envelope at the fundamental wavelength has been presented. Using a hyperbolic secant square function to model the mode-locked pulse, the temporal shape of a single Q-sw itched pulse at the second-harmonic wavelength has been reconstructed. The theoretical calculations of the pulse parameters like pulse energy, peak power, pulse width and pulse-symmetry factor have shown fairly good agreement with the experimental results. PACS 42.55.Rz; 42.55.Xi; 42.60.By     

Six-Watt mid-infrared laser using harmonic generation with Tl3AsSe3

An output of 6 W at 30 kHz was achieved using Tl₃AsSe₃ as the nonlinear second-harmonic generator. It was pumped with a CO₂ laser source at a wavelength of 9.25 m with 20 ns pulses, and the laser beam was focussed to a spot size of 150 m. The focussed spot was scanned to reduce the continuous-wave power loading, and the system could be operated for extended periods of time under these conditions.     

Compact efficient self-frequency Raman conversion in diode-pumped passively Q-switched Nd:GdVO<Subscript>4</Subscript> laser

I report the first demonstration of the generation of efficient sub-nanosecond self-stimulated Raman pulses by a diode-pumped passively Q-switched Nd:GdVO₄/Cr⁴⁺:YAG laser. The conversion efficiency for the average power is 7% from pump diode input to self-Raman output and the slope efficiency is up to 14%. At an incident pump power of 2.0 W, the pulse duration, pulse energy, and peak power for the Stokes wavelength of 1175.6 nm were found to be 750 ps, 6.3 J, and 8.4 kW, respectively, with a pulse-repetition rate of 22 kHz. PACS 42.55.Ye; 42.55.Xi; 42.60.Gd     

Comparative study on the laser performance of two Yb-doped disordered garnet crystals: Yb:CNGG and Yb:CLNGG

Continuous-wave (CW) and passively Q-switching laser performance of the Yb:CNGG and Yb:CLNGG disordered garnet crystals are compared. CW output powers of 6.3 and 7.5?W are generated from the Yb:CNGG and Yb:CLNGG lasers, with slope efficiencies measured to be 63 and 74?%, respectively. In passively Q-switched operation, the average output power reaches 2.0 and 3.1?W, with slope efficiencies of 56 and 65?%, for the Yb:CNGG and Yb:CLNGG lasers, respectively. Laser pulses of 9.5?ns in duration are generated with the two Yb lasers, with the highest pulse energy and peak power amounting to 166.7???J and 17.5?kW for the Yb:CNGG laser, and 133.0???J and 14.0?kW for the Yb:CLNGG laser. In respects of efficient laser operation and power scaling, the Yb:CLNGG proves to be advantageous over Yb:CNGG, whereas the Yb:CNGG is superior to Yb:CLNGG in energy storage capacity.     

3W average power 4.3 μm CO2 laser

A 3 W average power CO₂ laser oscillating in the range of 4.3m (10°1 to 10°O transition) is described. At the same time, the laser can emit 100 W in the sequence band 00°2 to 10°1 (10.6m). It is based on a commercial system with continuous-wave discharge of 12 m length and a slow gas flow. It operates in the Q-switched mode at pulse repetition rates up to 15 kHz. The pulse peak power is 1 kW and the pulse duration is 200 ns. The deviation from the theoretical efficiency limit has been decreased by a factor 2.5 in our device, due to saturation of the pumping (sequence band) radiation. We predict an improvement by another factor of 5 (possible average power of 10 to 20 W), if one avoids the absorption in the discharge-free zones.     

Passive Q switching and self-frequency Raman conversion in a diode-pumped Yb:KGd(WO(4))(2) laser

We report on the laser performance of a diode-pumped Yb:KGd(WO(4))(2) laser that is passively Q switched with a Cr(4+):YAG saturable absorber. Raman conversion of fundamental laser emission in the laser crystal was demonstrated. Q-switched 3.4-mu;J pulses with a pulse width of 85 ns were obtained at the 1033-nm fundamental wavelength and 0.4-mu;J pulses with a pulse width of 20 ns were produced in a first Stokes at 1139 nm.     

Optically pumped submillimeter laser lines from CH2F2 and CD2Cl2 using a12C18O2 CW laser

Thirty-nine new submillimetre laser lines in CH₂F₂ and twelve in CD₂Cl₂ have been obtained in a Fabry-Perot FIR resonator by optically pumping with a CW¹²C¹⁸O₂ laser. The wavelength range obtained for CH₂F₂ is 126m to 1091m and for CD₂Cl₂ 212m to 774m. The wavelength measurements are accurate to within 5.10^–3. The relative polarisations of the pump laser and the FIR laser output were also determined. Tentative assignments of the IR and FIR transitions were made using existing microwave data.     

Small-scale high-repetition-rate passively Q-switched intracavity OPO at 1.57 μm

A compact small-scale intracavity optical parametric oscillator (IOPO) at 1.57 μm, driven by a diode pumped Nd:YVO₄/Cr:YAG passively Q-switched laser, is experimentally presented. By optimizing the mode matching, low threshold (0.66 W) and high repetition rate (21 kHz) operation of the IOPO has been investigated. At the incident diode pump power of 1.56 W, the miniature (56 mm long) IOPO produces a signal average output power up to 86 mW. Efficient parametric conversion leads to short duration (1.8 ns) pulses and high peak power output (2.3 kW) at 1.57 μm. Moreover, near diffraction limited and Gaussian type signal beam profile is also observed.     

A high-power far-infrared NH3 laser pumped in a three-mirror CO2 laser cavity with optically-switched cavity-dumping

Results are reported of cavity-dumping a submillimeter radiation high-Q, zig-zag optically-pumped resonator which utilizes a silicon optical switch photo-excited by a NdYAG laser. Peak powers at 152 m approaching 10 kW in temporally smooth pulses of 5 ns (FWHM) duration have been obtained at a pulse repetition rate of 12 Hz. The far-infrared laser radiation, as measured with a scanning metal-mesh Fabry-Perot interferometer and averaged over many pulses, is, upon deconvolution of the 125 MHz instrumental linewidth, found to oscillate in a predominantly single longitudinal mode of width 250 MHz. Theoretical investigations of the transient far-infrared reflectivity of the silicon optical switch predict a rise in the Brewster-angle reflectivity from 0% to nearly 80% in 1 ns, when activated by a Q-switched, frequency-doubled NdYAG laser providing an incident energy density of 50 mJ/cm² in a pulsewidth of 10 ns.