Diode-pumped doubly Q-switched Nd:Lu0.33Y0.37Gd0.3VO4 laser with an electro-optic modulator and a single-walled carbon nanotube saturable absorber

By simultaneously using an electro-optic (EO) modulator and a single-walled carbon nanotube saturable absorber (SWCNT-SA) in the cavity, a diode-pumped doubly Q-switched Nd:Lu_0.33Y_0.37Gd_0.3VO₄ (Nd:LuYGdVO₄) laser is demonstrated. At the incident pump power 11.43 W and f=2 kHz, the minimum pulse width 17.6 ns and the maximum pulse peak power 19,886 W can be obtained. The experimental results show that this doubly Q-switched Nd:LuYGdVO₄ laser can generate shorter pulse width and higher peak power compared to the singly Q-switched Nd:LuYGdVO₄ laser with only EO or SWCNT-SA.     

Improvement of stability and pulse energy in a diode-pumped dual-loss-modulated QML Nd:Lu0.2Y0.8VO4 laser with EO modulator and GaAs

The Q-switched and mode-locked (QML) performance in a diode-pumped Nd:Lu_0.2Y_0.8VO₄ laser with electro-optic (EO) modulator and GaAs saturaber absorber is investigated. In comparison with the solely passively QML laser with GaAs, the dual-loss-modulated QML laser with EO and GaAs can generate pulses with higher stability and shorter pulse width of Q-switched envelope, as well as higher pulse energy. At the repetition rate 1 kHz of EO, the pulse width of Q-switched pulse envelope has a compression of 89% and the pulse energy has an improvement of 24 times. The QML laser characteristics such as the pulse width, pulse peak power etc. have been measured for different small-signal transmittance (T₀) of GaAs, different reflectivity (R) of output coupler and modulation frequencies of the EO modulator (f_e). The highest peak power and the shortest pulse width of mode-locked pulses are obtained at f_e = 1 kHz, R = 90% and T₀ = 92.6%. By considering the influences of EO modulator, a developed rate equation model for the dual-loss-modulated QML laser with EO modulator and GaAs is proposed. The numerical solutions of the equations are in good agreement with the experimental results.     

Multi-criteria optimization in CO2 laser ablation of multimode polymer waveguides

High interconnection density associated with current electronics products poses certain challenges in designing circuit boards. Methods, including laser-assisted microvia drilling and surface mount technologies for example, are being used to minimize the impacts of the problems. However, the bottleneck is significantly pronounced at bit data rates above 10 Gbit/s where losses, especially those due to crosstalk, become high. One solution is optical interconnections (OI) based on polymer waveguides. Laser ablation of the optical waveguides is viewed as a very compatible technique with ultraviolet laser sources, such as excimer and UV Nd:YAG lasers, being used due to their photochemical nature and minimal thermal effect when they interact with optical materials. In this paper, the authors demonstrate the application of grey relational analysis to determine the optimized processing parameters concerning fabrication of multimode optical polymer waveguides by using infra-red 10.6 µm CO₂ laser micromachining to etch acrylate-based photopolymer (Truemode^™). CO₂ laser micromachining offers a low cost and high speed fabrication route needed for high volume productions as the wavelength of CO₂ lasers can couple well with a variety of polymer substrates. Based on the highest grey relational grade, the optimized processing parameters are determined at laser power of 3 W and scanning speed of 100 mm/s.     

Doubly Q-switched GdVO4/Nd:GdVO4 laser with AO modulator and Cr4+:YAG saturable absorber under direct 879 nm diode pumping to the emitting level

In this letter, a doubly Q-switched 1.06 μm pulse laser with AO modulator and Cr⁴⁺:YAG saturable absorber by direct pumping grown-together composite GdVO₄/Nd:GdVO₄ crystal is demonstrated for the first time. Compared to purely AO Q-switching, the simultaneous use of AO Q-switch and Cr⁴⁺:YAG saturable absorber can generate shorter pulses and more symmetric temporal profiles. The thermal lens effect of laser crystal was analyzed.     

Diode-pumped Q-switched and mode-locked Nd:Gd0.3Lu0.33Y0.37VO4 laser with EO modulator and single-walled carbon nanotube

By using both the single-walled carbon nanotube saturable absorber (SWCNT-SA) and the electro-optic (EO) modulator, the stably doubly Q-switched and mode-locked (QML) operation of Nd:Gd_0.3Lu_0.33Y_0.37VO₄ laser has been demonstrated. The QML laser characteristics such as the pulse width, single-pulse energy, etc., have been measured for different modulation frequencies of the EO modulator (f_e) and reflectivity (R) of output coupler. In comparison with the solely passively QML laser with SWCNT-SA, the experimental results show that the doubly QML laser can generate more stable and shorter pulses with higher pulse energy. At 9.24 W pump power, f_e=1 kHz and R=93.5%, the doubly QML laser has compressed the Q-switched envelope pulse width 88% and improved the mode-locked pulsed energy 55 times.     

Combustion of micron-sized particles of titanium and zirconium

Particles of titanium and zirconium in the size range of 2–25 μm are ignited while passing through a CO₂ laser beam and their combustion is monitored optically. Prior to ignition, particles pass through a low-power auxiliary laser beam so that the diameter of each ignited particle is measured in situ based on the amplitude of the scattered light pulse. The particles of both Ti and Zr are observed to exhibit micro explosions, similar to those observed for larger size particles of these metals. Particle emission traces are recorded, and a data processing routine is established for discounting emission signals produced by unignited particles and particles partially combusted within the CO₂ laser beam. Burn times and combustion temperatures are measured and compared to earlier measurements for coarser particles of the same metals. For both metals, average combustion temperatures implied by the emission spectra are very close to their respective adiabatic flame temperatures. For both metals, for the particle size range considered, particle combustion temperatures do not depend on the particle size. The particle burn times were found to be only weak functions of the particle size; burn times for Zr are shorter and temperatures are higher compared to the similarly sized Ti particles.     

Miniature high-repetition-rate TEA CO2 laser with surface-wire-corona preionization

In this article, an experimental study of a miniature, sealed-off, high-repetition-rate transversely excited atmospheric-pressure (TEA) CO₂ laser with a kind of surface-wire-corona preionization (SWCP) is described. We have utilized an SWCP consisting of SiO₂ dielectric tube and a fine wire strained and attached to the dielectric surface. A BN ceramic material, which has an extremely low coefficient of thermal expansion of about 5 × 10⁻⁷/°C was employed as a supporter of the resonator. A measurement on emission spectra of SWCP has been reported. By applying SWCP to the TEA CO₂ laser, efficient laser operation at an overall efficiency of 9.8% with an output energy of 150 mJ has been achieved from a small discharge volume of 25 cm³ with an active length of 230 mm. At the pulse repetition frequency of 60 Hz, the TEM₀₀ mode of laser beam with pulse width of 60 ns was obtained.     

Passively Q-switched diode-pumped Raman laser with third-order Stokes eye-safe oscillation

We demonstrate a passively Q-switched all-solid-state laser system with intracavity Raman frequency conversion to the eye-safe spectral region. Laser oscillation at the 1.064 μm wavelength with a pulse repetition rate of several kilohertz was provided by a Nd:YAG crystal and a Cr:YAG passive absorber. Third Stokes oscillations at the 1.599 and 1.494 μm wavelengths were obtained in Ba(NO₃)₂ and PbWO₄ crystals with output pulse energies of 5 μJ and 6 μJ, respectively. The results of the numerical simulation of the pulse dynamics are in good agreement with the experimental data.     

The influence of thermal lens effect on pulse repetition rate in diode-pumped passively Q-switched Nd:GdVO4/V:YAG laser

The influence of thermal lens effect on pulse repetition rate in diode-pumped Nd:GdVO₄ 1.34 μm laser has been demonstrated. The repetition rate first increased, then reduced with augment of the pump power, for V:YAG with initial transmission (T₀) of 96%. The maximum repetition rate was 70 kHz, obtained at the pump power of 6.78 W. The best output laser characteristics—the pulse width of 39.2 ns, the peak power of 2.5 kW and the single pulse energy of 102 μJ—were obtained by V:YAG of T₀=89%. With the Gaussian spatial distribution of intracavity photon density being considered, the rate equations were solved numerically and the theoretical calculations agreed with the experimental results.     

1.34 μm fluorescence and laser properties of Nd:La0.11Y0.89VO4 crystal

For Nd:La_xY_1−xVO₄ (x = 0.11) crystal, the ⁴F_3/2 → ⁴I_13/2 transition property was investigated for the first time. The fluorescence peak of Nd:La_0.11Y_0.89VO₄ crystal exhibited obvious inhomogeneous broadening comparing with that of Nd:YVO₄ crystal. With laser diode array as pump source, 1.34 μm continuous-wave (CW) and active Q-switched laser operations based on ⁴F_3/2 → ⁴I_13/2 transition were realized. For CW laser operation, the maximum output power of 2.47, 2.13 W is obtained with slope efficiencies of 29.4%, 27.6%, and optical to optical conversion efficiency of 26.2%, 24.7%, respectively for a, c cut crystal samples. For acousto-optic (AO) Q-switched laser operation, the shortest pulse width, highest peak power and maximum pulse energy came from the a-cut sample, which were 13 ns, 2.69 kW and 35 μJ, respectively.     

Fast femtosecond laser ablation for efficient cutting of sintered alumina substrates

Fast, accurate cutting of technical ceramics is a significant technological challenge because of these materials' typical high mechanical strength and thermal resistance. Femtosecond pulsed lasers offer significant promise for meeting this challenge. Femtosecond pulses can machine nearly any material with small kerf and little to no collateral damage to the surrounding material. The main drawback to femtosecond laser machining of ceramics is slow processing speed. In this work we report on the improvement of femtosecond laser cutting of sintered alumina substrates through optimisation of laser processing parameters. The femtosecond laser ablation thresholds for sintered alumina were measured using the diagonal scan method. Incubation effects were found to fit a defect accumulation model, with F_th,1=6.0 J/cm² (±0.3) and F_th,∞=2.5 J/cm² (±0.2). The focal length and depth, laser power, number of passes, and material translation speed were optimised for ablation speed and high quality. Optimal conditions of 500 mW power, 100 mm focal length, 2000 µm/s material translation speed, with 14 passes, produced complete cutting of the alumina substrate at an overall processing speed of 143 µm/s – more than 4 times faster than the maximum reported overall processing speed previously achieved by Wang et al. [1]. This process significantly increases processing speeds of alumina substrates, thereby reducing costs, making femtosecond laser machining a more viable option for industrial users.     

An experimental study of an acousto-optic Q-switched Yb3+-doped all-fiber laser

The Q-switched fiber lasers are very attractive sources in many applications such as military affairs, surgical operation, laser machining, laser marking, nonlinear frequency conversion, range finding, remote sensing and optical time domain reflectometer. In this paper, an acousto-optic Q-switched Yb³⁺-doped all-fiber laser at 1083 nm is reported. The pulse energy of 2.94 mJ has been obtained at the pump power of 8.47 W, and the pulse width is 3 μs.     

Passively Q-switched a-cut Nd:GdVO4 self-Raman laser with Cr:YAG

A passively Q-switched a-cut Nd:GdVO₄ self-Raman solid-state laser with Cr:YAG saturable absorber was firstly demonstrated. The first Stokes at 1173 nm was successfully obtained. At the maximum incident pump power, the pulse width was about 1.8 ns and the repetition rate was 27.5 kHz. 586.5 nm yellow laser output was also realized by use of an LBO frequency doubling crystal.     

Hard tissue ablation with a free running Er:YAG and a Q-switched CO2 laser: a comparative study

The Er:YAG and the CO₂ laser are competitors in the field of hard tissue ablation. The use of Er:YAG lasers (2.94 μm, pulse length _L of 100 to 200 μs) show smaller areas of thermal defects then ‘‘superpulsed’’ CO₂ lasers with pulse lengths of approximately 100 μs. Only the development of a Q-switched CO₂ laser (9.6 μm, τ_L=250 ns) allowed for similar results. In this paper new results for the Er:YAG and the Q-switched CO₂ laser under the influence of water spray will be presented. Several parameters are of special interest for these investigations: the specific ablation energy, which shows a minimum for the CO₂ laser at an energy density of 9 J/cm ² and a broad shallow minimum in the range of 10 to 70 J/cm² for the Er:YAG laser, and comparison of the cut-shape and depth. Surface effects and cutting velocity are discussed based on SEM pictures. Received: 19 July 2000 / Revised version: 1 November 2000 / Published online: 30 November 2000     

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%.     

High pulse repetition frequency RF excited waveguide CO2 laser with mechanical Q-switching

In this paper, a mechanical Q-switching is used in radio frequency (RF) excited waveguide CO₂ laser to obtain high pulse repetition frequency (PRF) laser. The Q-switching system includes two confocal ZnSe lenses and a high speed mechanical chopper, which is inserted into the cavity. The peak power is up to 730 W and the pulse width 200 ns at the highest PRF 20 kHz. The laser also has the advantages of compact, small-volume, and low-cost.     

2 μm passive Q-switched mode-locked Tm3+:YAP laser with single-walled carbon nanotube absorber

We report the first demonstration, to our knowledge, of passive Q-switched mode-locking in a Tm³⁺:YAP laser, operating in the 2 μm broadly spectral region formed with a compact Z-flod cavity. A transmission-type single-walled carbon nanotube saturable absorber (SWCNT–SA) is used for the initiation of the pulse generation. The repetition rate of the Q-switched envelope was 60 kHz at the pump power of 8.6 W. The mode-locked pulses inside the Q-switched pulse envelope had a repetition rate of ～92 MHz. A maximum average output power of 761 mW was obtained. The dependence of the operational parameters on the pump power was also investigated experimentally.     

Surface engineering of biomedical metallic materials by plasma-based low-energy ion implantation

Plasma-based low-energy ion implantation, including plasma source ion nitriding/carburizing and plasma source low-energy ion enhanced deposition of thin films, for surface engineering of metallic materials was emerged as low-temperature, low-pressure surface modification technique. Plasma source ion nitriding onto AISI 316L austenitic stainless steel produced a high nitrogen face-centered-cubic phase (γ_N) layer about 10 μm thick at the temperature of 380 °C during 4 h with the high microhardness of HK_0.1 N 22.0 GPa. The microhardness of the nitrided surface from the titanium nitride phase [(Ti, Al, V)N] layer on Ti6Al4V alloy at 750 °C during 4 h achieved up to about HK_0.1 N 15.5 GPa. No pitting corrosion in the Ringer’s solution at 37 °C was detected by electrochemical polarization measurement for the nitrided AISI 316L stainless steel and Ti6Al4V alloy, respectively. Plasma source ion nitriding of the metallic materials provided the engineering surfaces with combined improvement in hardness and corrosion resistance.     

Cavity-dumped electro-optical Q-switched Nd:GdVO4 laser with high repetition rate

We reported a cavity-dumped operation of electro-optical Q-switched Nd:GdVO₄ laser at high repetition rates for the first time. A constant 5.5 ns pulse duration was realized. The maximum average output power was 5.1 W at the highest repetition rate of 50 kHz, corresponding to a peak power of 18.5 kW.     

High-power eye-safe KTA-OPO driven by YVO4/Nd:YVO4 composite laser

We present a high-power 1.53 μm laser based on intracavity KTA-OPO driven by diode-end-pumped acousto-optical Q-switched YVO₄/Nd:YVO₄ composite. The composite crystal was utilized for reducing the thermal effect, and the mode mismatch compensating OPO cavity was designed for efficient OPO conversion. The output power of eye-safe laser at 1535 nm was up to 4.4 W with the pump power of 27 W, corresponding to a diode-to-signal conversion efficiency of 16.3%. To our knowledge, this is the highest output power in diode-end-pumped circumstances. In the experiment, the strong yellow light generated by Raman conversion and frequency doubling in the KTA crystal was observed.