Laser output power over 5 W at 1.06 μm for Nd:GdVO4 single crystal

In this paper, we report the polarization absorption spectra from 400 to 850 nm, polarization emission spectra from 1050 to 1100 nm and laser properties of an Nd:GdVO₄ crystal. An output power of up to 5.29 W at 1.06 μm has been achieved with a 3×3×3 mm Nd:GdVO₄ crystal sample when it is pumped by a cw laser diode.     

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.     

Continuous-wave and passively Q-switched Nd:GdVO4 lasers at 1.06 μm end-pumped by laser-diode-array

We demonstrated a diode-end-pumped continuous-wave and passively Q-switched Nd:GdVO₄ laser operating at 1.06 μm wavelength with a three-mirror folded resonator. The maximum continuous-wave output power of 8.18 W was obtained at the incident pump power of 22.5 W, with the corresponding optical conversion efficiency of 36.4%. For Q-switched operation, the maximum average output power was measured to be 4.64 W with the corresponding optical conversion efficiency of 25.8%, when the initial transmission of Cr⁴⁺:YAG crystal was 90%. The shortest pulse width of 83 ns, the largest pulse energy of 20.7 μJ and the highest peak power of 246.7 W were obtained when the Cr⁴⁺:YAG crystal with an initial transmission of 85% was used.     

Passively Q-switched Nd:GdVO4 laser with In0.25Ga0.75As being an output coupler

We report a diode-end-pumped passively Q-switched Nd:GdVO₄ laser operating at 1.06 μm with In_0.25Ga_0.75As being the saturable absorber as well as an output coupler. Q-switched pulses with a pulse duration of 20 ns, pulse energy 4.2 μJ and pulse repetition rate 200 kHz were produced, corresponding to peak power of 210 W.     

Plasma-mediated ablation of brain tissue with picosecond laser pulses

Plasma-mediated ablations of brain tissue have been performed using picosecond laser pulses obtained from a Nd:YLF oscillator/regenerative amplifier system. The laser pulses had a pulse duration of 35 ps at a wavelength of 1.053 µm. The pulse energy varied from 90 µJ to 550 µJ at a repetition rate of 400 Hz. The energy density at the ablation threshold was measured to be 20 J/cm². Comparisons have been made to 19 ps laser pulses at 1.68 µm and 2.92 µm from an OPG/OPA system and to microsecond pulse trains at 2.94 µm from a free running Er:YAG laser. Light microscopy and scanning electron microscopy were performed to judge the depth and the quality of the ablated cavities. No thermal damage was induced by either of the picosecond laser systems. The Er:YAG laser, on the other hand, showed 20 µm wide lateral damage zones due to the longer pulse durations and the higher pulse energies.     

Compact eye-safe laser sources based on OPOs with KTP or PPKTP crystals

We report on compact eye-safe nanosecond laser sources emitting in the 1.5 μm wavelength range based on non-critically phase-matched parametric interaction in optical parametric oscillators (OPOs) with KTP and periodically poled KTP (PPKTP) crystals, pumped by the fundamental frequency of Nd:YAG lasers. As much as 250 μJ signal pulse energy at 1.5 μm wavelength, 6.5 ns FWHM pulse-width, has been obtained in a PPKTP-OPO, extracavity pumped by a Nd:YAG microlaser oscillator–amplifier at 650 μJ pump pulse energy, 8 ns pulse-width. A single signal pulse of 2.7-mJ output energy at 1.57 μm wavelength, less than 5 ns pulse-width, was generated in a KTP-OPO, intracavity pumped by a passively Q-switched Nd:YAG laser.     

Spectroscopic and laser properties of Nd:Gd0.8La0.2VO4 crystal

The polarised absorption and fluorescence spectra of Nd:Gd_0.8La_0.2VO₄ crystal are measured and compared to those of Nd:GdVO₄. CW laser properties of diode-pumped Nd:Gd_0.8La_0.2VO₄ crystal operating at fundamental wavelengths of 1.06 and 1.34 μm, as well as when intracavity frequency-doubled to 532 and 670 nm, have been studied. The maximum output powers at 1.06 μm, 1.34 μm, 532 nm and 670 nm are 1.18 W, 671 mW, 206 mW and 42 mW respectively, at a diode-launched pump power of 2.9 W. The threshold pump powers are 80, 267, 7 and 15 mW respectively.     

Passively Q-switched Nd:LuVO4 laser using Cr:YAG as saturable absorber

A passively Q-switched all solid-state Nd:LuVO₄ 1.06 μm laser was demonstrated by using Cr⁴⁺:YAG as saturable absorber. The characteristics of average output power, pulse width, repetition rate, pulse energy, and peak power were studied with different output couplings and initial transmission of saturable absorbers. When output coupling with the transmission of 20% was used, the shortest pulse width of 16 ns at the repetition rate of 12.5 kHz was obtained, which results in the pulse energy of 71 μJ and peak power of 4.43 kW with the initial transmission of 70% of Cr⁴⁺:YAG crystal.     

LD-pumped passively Q-switched Nd:YVO/LBO red laser with V:YAG

An LD-pumped Nd:YVO₄ passively Q-switched by V:YAG and intracavity frequency doubled by LBO red pulse laser at 671 nm was presented. With 1.6 W incident pump power, average output power of 53 mW, pulse duration (FWHM) of 29.5 ns, pulse repetition rate of 37.2 kHz, peak power of 48.3 W and single-pulse energy of 1.43 μJ were obtained. The stability of pulse energy and repetition rate was better than 3% for 4 h.     

IR-induced nonlinear optics in Ge-doped Bi12TiO20 large-sized nanocrystallites

Photoinduced non-linear optical effects in large-sized (up to 25 nm) nanocrystallites (NC) of Ge-doped Bi₁₂TiO₂₀ (BTO:Ge) incorporated within olygoether photopolymer matrix have been studied. Photoinduced second harmonic generation (PISHG) was measured. Nd:YAG pulsed laser (λ=1.06 μm) was used as a source of photoinducing light. As a fundamental light source for the SHG and two-photon absorption, Er:LiYF₄ laser (λ=2.065 μm) was used. We have found that with increasing IR pump power density, the output doubled frequency SHG signal (λ=1.03 μm) increases and achieves its maximum value at the pump power density about 0.45 GW/cm² and NC size about 12 nm.The values of second-order optical susceptibilities were almost 20% larger than for the pure BTO NC single crystals. With decreasing temperature below 60 K, the SHG signal increases achieving maximal value at LHeT.     

Pulsed infrared radiation transmission through chalcogenide glass fibers

Two different kinds of chalcogenide glass IR fibers were evaluated relative to transmission of pulsed IR radiation produced by several laser sources in the wavelength range from 1 to 10 μm. Fibers composed either from As-Se-Te or from As₂S₃ glass, of 250, 500, 750 and 1000 μm and 250, 750 and 1000 μm core diameters were studied, respectively. Attenuation measurements were obtained as a function of the laser energy input and as a function of curvature, wherever this was possible. The output beam quality was also studied using a beam profiler. The lasers used were a Q-switched Nd:YAG laser, emitting at 1.06 μm, a free-running or Q-switched Er:YAG laser emitting at 2.94 μm and a tunable pulsed CO₂ laser emitting in the range of 9.3-10.6 μm. The fibers exhibited better behavior when tested with the Er:YAG laser and they were found fragile in pulsed radiation from the Nd:YAG and the CO₂ laser. The output beam profiles generally showed a central multi-spiking energy distribution.     

高重频2.94 μm Er:YAG激光器的研究

分析了Er3+离子的能级结构特性和Er:YAG四能级系统的激光速率方程。采用了双灯,双椭圆腔和窄脉冲放电等方式提高了抽运效率; 通过提高激光谐振腔的反射率,降低阈值,从而实现了输出2.94 μm的高重频窄脉冲激光; 采用高压高速层流冷却技术降低了热效应的影响。Er3+:YAG激光器的重复频率为40 Hz,单脉冲输出能量为0.5 J,满足实际应用需要。     

Actively Q-switched intracavity second-harmonic generation of 1.06 μm in BiB3O6 crystal

We have investigated the acousto-optically Q-switched intracavity second-harmonic generation of 1.06 μm in a 1.9-mm-long BiB₃O₆ crystal, cut for type-I phase-matching direction of (θ,)=(168.9°,90°), performed in a diode-end-pumped Nd:YVO₄ laser. When the incident pump power was 4.3 W at 30 kHz of pulse repetition frequency, a maximum average green output power of 480 mW, the shortest pulse with FWHM width of 72 ns, the highest single pulse energy of 16 μJ and the maximum peak power of 222 W were obtained, giving the corresponding optical conversion efficiency of 11.2%. The effect of varying temperature in BIBO crystal on the average green output power was also investigated.     

Characteristics of a passively Q-switched Nd:NaY(WO4)2 laser with Cr:YAG saturable absorber

By using xenon flash lamp as pump source and Cr⁴⁺:YAG as passive Q-switcher, we have performed the Q-switched laser operation at 1.06 μm with an Nd³⁺:NaY(WO₄)₂ (known as Nd:NYW) crystal. Meanwhile, the pulse width, the single pulse energy and the repetition rate under different small-signal transmissions of Cr⁴⁺:YAG and different reflectivities of output reflector are measured, and the numerical solutions of the coupling wave rate equations agree with the experimental results.     

Spike suppression and longitudinal mode selection in a 1.319 μm Nd:YAG laser by high-efficiency intracavity frequency doubling

We describe a flashlamp pumped 1.319 μm Nd:YAG ring laser in which a high-efficiency intracavity frequency doubler is used as a nonlinear output coupler, virtually eliminating all spiking behavior and providing longitudinal mode selection as well. A single frequency, long pulse (>50 μs) output at 660 nm with about 20 W peak power is produced, suitable as a source for visar and other applications where long coherent pulses at relatively high power are required. Experimental results and theoretical analyses are given.     

Manifestation of hexagonal-like structure in the second-order nonlinear effects in the GaN nanocrystallites

Contribution of the hexagonal-like structural components to the photoinduced second harmonic generation (SHG) in GaN large-sized nanocrystallites (with sizes about the 10–30 nm) incorporated into the polyvinylalcohol photopolymer matrices is revealed. The SHG measurements were done using pulsed Nd:YAG laser beam (λ=1.06 μm; pulse duration τ=15–50 ps, laser power about 30 MW) as a fundamental ones and a picosecond nitrogen pulsed laser (P=10 MW; λ=0.377 μm; pulse time duration τ=10–25 ps) as a photoinducing one. We have found that with increasing pumping power density the SHG output signal increases and achieves its maximum value for the power density about 2.6 GW/cm² per pulse. The maximal output photoinduced SHG signal was achieved for parallel directions of the pumping and fundamental beam polarizations. The maximal values of the second-order nonlinear susceptibilities were equal to about 1.09 pm/V. We have observed an increase of the output SHG below 30 K and for pump-probe delaying time about 18 ps. Substantial contribution to the SHG of wurtzite-like (hexagonal) structural fragments is shown.     

New and simple method for fabricating polymer-coated silver hollow fibers with large mechanical strength

A new method is proposed for fabricating polymer-coated silver hollow glass fibers to avoid the flexibility deterioration after the curing process. Transmission properties of fibers made by the two procedures with and without curing process are compared. Little difference was observed in the transmission properties at the wavelength 2.94 μm of Er:YAG laser light and 10.6 μm of CO₂ laser light. The polymer layer is shown to be stable after 2-h, 5-W, continuous wave CO₂ laser light transmission.     

High-energy Q-switched operation of a fiber-laser-pumped Er:YAG laser

A high-energy Q-switched Er:YAG laser in-band pumped by an Er,Yb co-doped fiber laser is reported. A simple two-mirror multi-mode resonator incorporating an electro-optic Q-switch and a multi-Brewster-plate polarizer was employed, together with a simple compensation scheme to reduce the depolarization loss due to thermally induced stress birefringence in the Er:YAG crystal at high pump powers. The laser yielded Q-switched pulses at 1617 nm with 30.5-mJ pulse energy and <20-ns pulse duration (FWHM) at 20-Hz repetition rate, corresponding to a peak power of >1.5 MW for 55 W of pump power at 1532 nm. The prospects for further improvement in Q-switched performance are discussed.     

Q-switched NYAB laser end-pumped by a high-power diode-laser array

A diode-laser array end-pumped acousto-optically Q-switched NYAB laser operating at both 1.06 and 0.53 μm has been demonstrated. An average output power of 1.3 W at 1.06 μm at a pulse repetition frequency (PRF) of 60 kHz was obtained with an optical conversion efficiency of 18.1% and a slope efficiency of 21.3%. At the incident pump power of 6.1 W, the 1.06 μm shortest laser pulse was reached at PRF of 20 kHz with FWHM width measured to be 32 ns, yielding a largest pulse energy of 30 μJ, and a highest peak power of 938 W. The attainable maximum average green power was found to be 185 mW, with an optical conversion efficiency of 3%.     

Single axial mode Q-switched pulse generation at 1.052 μm by self seeding in a Nd: YAG oscillator

Single axial mode Q-switched pulse generation at 1.052 μm in Nd:YAG by self seeding with free running spikes is discussed. The Nd:YAG, having plane parallel faces without anti-reflection coatings, exhibits modulation-free spikes in the free running regime. By allowing the Q-switching to take place, when the radiation field of any of these pulses is present in the resonator, very reliable and reproducible modulation-free Q-switched pulses are obtained.