Q-switched Intracavity Optical Parametric Oscillator Research Articles

Experimental optimization and dynamics solution of active-passive Q-switched intracavity optical parametric oscillator based on EO modulator and layered-WSe2 SA

By applying a prepared 3 nm-thick tungsten diselenide (WSe2) saturable absorber to an electro-optic (EO) modulated fundamental-light laser, an active and passive Q-switched intra-cavity optical parametric oscillator (IOPO) has been experimentally realized. Benefiting from the saturable absorption property of WSe2, the output characteristics of Q-switched IOPO with signal-light oscillating are obviously improved, including the 93.7%-increased peak power, 54.6%-compressed pulse width, 30.1%-improved conversion efficiency, 60.1%-improved pulse-train stability, 17.8%-improved beam quality, and 27.4%-shortened linewidth. With the values of absorption parameters calculated from the measured nonlinear-transmittance curve of WSe2, the rate equations for dual-loss Q-switched IOPO with WSe2 saturable absorber and electro-optic modulator are numerically solved. The theoretical values correspond to the experimental data well.

An active and passive dual-loss Q-switched intracavity OPO based on few-layer WS2 saturable absorber

A 2.5 nm-thickness tungsten disulfide (WS2) saturable absorber (SA) was successfully fabricated by the electron beam evaporation (EBE) combined with post vulcanization. By applying the prepared WS2 SA to an acousto-optic (AO) Q-switched fundamental laser, a dual-loss-modulated Q-switched intracavity optical parametric oscillator (IOPO) has been experimentally realized. Because of the participation of WS2 SA, the problem of output decline was alleviated when the pump power was between 8.6 W and 10.8 W. The pulse width could be maximally compressed by 73% in WS2 SA based active-passive Q-switched IOPO with 10 kHz pulse-repetition rate, and the shortest pulse width in experiment was 1.098 ns. Benefiting from the pulse compression, the maximum pulse peak power in dual-loss-modulated Q-switched IOPO was 427% higher than that in AO active Q-switched IOPO. The application of WS2 SA also contributed to the stability of signal pulse train whose root mean square error (RMS) was efficiently lowered from 0.01776 to 0.00954. The nonlinear conversion efficiency was improved by approximate 38.2% in the dual-loss-modulated Q-switched IOPO.

Investigation of thermal induced diffraction loss on Q-switched intracavity optical parametric oscillator

In this paper the influence of thermal induced diffraction loss on the optical parametric oscillator has been investigated numerically by analysing the rate equations model. The model has been performed to the practical example of Q-switched Nd:YVO4-KTA optical parametric oscillator to verify the theoretical model. The numerical analysis shows that the signal output power can be maximized for unique pump beam radius. The pump beam radius is calculated to be 297μm which is reported 300μm from experimental results.

Double-prism domain PPLN for simultaneous laser Q-switching and optical parametric oscillation in a Nd:YVO_4 laser

We report a design and demonstration of an electro-optically Q-switched intracavity optical parametric oscillator (IOPO) based on a unique ramped duty-cycle periodically poled lithium niobate (PPLN) in a diode-pumped 1064-nm Nd:YVO(4) laser. The PPLN crystal, having a double-prism domain (DPD) structure with a domain period of 30 μm, can work simultaneously as an electro-optic (EO) beam deflector (and therefore an EO Q-switch in the laser cavity) and an optical parametric down converter. The characterized deflection sensitivity of the DPD PPLN device was 1.15°/kV-cm. At a 180-V Q-switching voltage and a 1-kHz switching rate, we measured a down-converted signal at 1550 nm with pulse energy of >8.1 μJ (or peak power of >2.3 kW) from the constructed IOPO at 7.5-W diode pump power. Continuous wavelength tuning of the IOPO signal was also demonstrated.

Theoretical and experimental studies on passively Q-switched KTiOAsO4 optical parametric oscillator

A passively Q-switched intracavity optical parametric oscillator based on KTiOAsO4 (KTA) crystal is studied theoretically and experimentally. The rate-equation-based theoretical model is established to describe the time evolutions of the population inversion density of the laser crystal, ground-state population density of the saturable absorber, fundamental photon density, signal photon density and the idler photon density. In the experiment, a laser diode-end pumped, passively Q-switched Nd:YAG/KTA IOPO with a Cr4+:YAG crystal as the saturable absorber is realized to verify this model. The characteristics including the output power, the pulse repetition rate, the pulse width and the beam quality were investigated for this OPO. The experimental results for the output power and the repetition rate agree with the theory well. And both results show that with same pumping level the idler pulse width is shorter than the signal one.

Laser-diode-pumped doubly Q-switched Nd:GdVO4/KTA intracavity optical parametric oscillator

By using an acousto-optic (AO) modulator and a Cr4+:YAG saturable absorber, a high repetition rate doubly Q-switched noncritically phase-matched KTiOAsO4 (KTA) intracavity optical parametric oscillator (IOPO) at 1.50 μm is realized. In comparison to AO Q-switched IOPO, the lower threshold energy, the higher output average power, the narrower pulse width and the higher peak power from the doubly Q-switched IOPO can be obtained.

Electro-optic Q-switched intracavity optical parametric oscillator at 1.53 μm based on KTiOAsO4

An eye-safe, high peak power optical parameter oscillator (OPO) intracavity pumped by electro-optic Q-switched Nd:YAG laser is presented. This OPO is based on a 20mm length KTiOAsO4 crystal with non-critical phase matching (θ=90°, ϕ=0°) cut. An aperture ∅3mm acted as limiting diaphragm to get good beam quality of pumping laser. The output energy of 25mJ at the signal wavelength 1.53μm was obtained with repetition rate of 1Hz. The highest peak power intensity was up to 88MW/cm2 with pulse width of 4ns. Without diaphragm, the maximum output energy of 90mJ was achieved with area of light spot (∅6mm) four times larger, but the peak power intensity was lower.

Analysis of output characteristics of the actively Q-switched intracavity optical parametric oscillator considering Gaussian distribution of intracavity photon densities

By considering the Gaussian spatial distribution of the initial population-inversion density and the intracavity photon densities of the fundamental, the signal and the idle lights, the rate equations of a LD-pumped actively Q-switched intracavity optical parametric oscillator (IOPO) are derived. The influence of the pump rate, the thermal effect in the gain medium and the change of the photon density along the cavity axis have also been taken account in the equations. By numerically solving these coupled equations, the dependences of pulse width, pulse energy and peak power on incident pump power for the generated-signal light are obtained. In the experiment, a laser-diode-pumped actively Q-switched Nd:GdVO4/KTP IOPO with an acousto-optic (AO) modulator is realized and the experimental results agree with the theoretical calculations.

Pulse compression and threshold decrease in high- repetition-rate doubly Q-switched intracavity optical parametric oscillator

By using RbTiOPO4 (RTP) crystals as an electro-optic (EO) modulator and Cr4+:YAG saturable absorber as a passive Q switch, a high repetition rate doubly Q-switched intracavity optical parametric oscillator (IOPO) is realized. In comparison to an EO Q-switched IOPO, the lower threshold energy, the higher output energy, the narrower pulse width, and the higher conversion efficiency from the doubly Q-switched IOPO can be obtained. By considering the gradual loss from the delayed switched time of the EO switch, the coupled rate equations of doubly Q-switched IOPO under the assumption of the uniform distributions of the intracavity photon densities are given, and the numerical solution of the equations fits the experimental data well.

Pulse Compression in Laser-Diode-Pumped Doubly Q-Switched Intracavity Optical Parametric Oscillator Considering Gaussian Distribution of Intracavity Photon Densities

By considering the Gaussian spatial distribution of the initial population-inversion density and the intracavity photon densities of the fundamental, the signal and the idler lights, the rate equations of a laser-diode (LD) end-pumped doubly Q-switched intracavity optical parametric oscillator (IOPO) with both acousto-optic (AO) modulator and Cr4+:YAG saturable absorber are derived. By numerically solving these coupled equations, the dependences of pulse width, pulse energy and peak power on incident pump power for the generated-signal light, whose wavelength is 1.57 µm, are obtained. In the experiment, a LD-pumped doubly Q-switched Nd:GdVO4/KTP (KTiOPO4) IOPO with AO and Cr4+:YAG saturable absorber is realized. The experimental results are compared with those of the AO singly Q-switched IOPO. The doubly Q-switched IOPO can generate the shorter pulse width and higher peak power than that of the AO singly switched one when the input diode power is about from 5.2 to 6 W. The experimental results agree with the theoretical values well.

Temporal behavior of the laser pulse for intracavity optical parametric oscillator

We describe a compact, end-pumped all-solid-state, and Q-switched intracavity optical parametric oscillator (OPO). With this design, the relaxation oscillation type of multi-pulses produced in the intracavity OPO is eliminated. The intracavity OPO is based on periodically poled RbTiOAsO(4) (PPRTA) as the nonlinear material and is pumped by a compact diode-pumped Yb:YAG Q-switched laser at a wavelength of 1.030 microm. The pulse width (FWHM) is about 11 ns at the full pump power for both the signal and idler pulses. Output energies of 384 microJ at idler wavelength and 615 microJ at signal wavelength are obtained. We demonstrate a Q-switched IPOPO oscillator that operates the signal and idler wavelengths without relaxation oscillation type multi-pulses and with fast wavelength tuning ability for both signal and idler wavelength.

Output optimization of a high-repetition-rate diode-pumped Q-switched intracavity optical parametric oscillator at 1.57�?m

The output optimization of a high-repetition-rate diode-pumped Q-switched intracavity optical parametric oscillator at 1573 nm with a type-II non-critically phase-matched x-cut KTP is experimentally and theoretically studied. The optimum output reflectivity is found to be 85–90% for the maximum average power. The average conversion efficiency from diode-laser input power to OPO signal output power is up to 15% at a pulse repetition of 80 kHz. However, the optimum output reflectivity for the maximum peak power is found to be 60–70%; the overall peak power amounts to 3–4 kW at a pulse repetition of 80 kHz.