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

Abstract

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.

Investigations of 2D PtS2’s Saturable Absorption Characteristic and Its Optimization to OPO’s Operation

“…In theory, Q-switching dynamics is well explained by rate equations [ 32 ]. In this section, the Gaussian assumption and PtS 2 ’s characteristic were considered for the dynamical model of a Q-switched Nd:YVO 4 /KTP IOPO with AO active time-management.…”

“…The IOPO rate equation with the saturable absorption characteristic of PtS 2 SA is obtained by referring to the previous research work [ 26 , 27 , 32 , 33 ]. …”

“…In Equation (4), δ T is the diffractive loss caused by the gain medium’s thermal effect. δ a ( t ) can be written as [ 32 ], where t AO and δ a are the turn-off time and the intrinsic diffraction loss of the AO Q-switch. δ a ( t ) is used to describe the loss function of the gradual AO modulator (AOM) caused by the exponential time delay.…”

“…δ a ( t ) is used to describe the loss function of the gradual AO modulator (AOM) caused by the exponential time delay. The basic parameters for calculating the rate equation refer to previous work [ 32 , 33 , 34 , 35 ].…”

“…With the average output power and the repetition frequency of the pulse, the pulse energy of the signal light could be calculated by E pulse = P average / f p , which is shown in Figure 5 e,g. Then, the peak power was calculated by P peak = E pulse /W, where W is the full width at half maximum (FWHM) of the signal pulse [ 32 ], shown in Figure 5 f,h. Owing to the pulse compression of PtS 2 SA, the peak power of dual-loss Q-switched IOPO increased 131% from 1.815 kW in single Q-switched IOPO to 4.193 kW in doubly Q-switched one at 5.2 W pump power.…”