The modified Frantz–Nodvik equation considering the pulse repetition rate (PRR) for continuous-wave end-pumped picosecond laser amplifier is theoretically developed for the first time by analogizing Q-switch theory and solving rate equations. Based on the modified Frantz–Nodvik equation, a simple finite-element slice model is established to simulate the output characteristics of the end-pumped high-repetition-rate picosecond amplifier. Moreover, the validity of the theory and model is well verified by the experimental results of a two-staged diode-end-pumped Nd : YVO4 amplifiers using a picosecond fiber laser with adjustable PRRs as the seed source. The agreement between the experimental and theoretical results illustrates that the as-developed pulse amplification theory and model are a powerful tool for designing and optimizing adjustable-high-repetition-rate solid-state picosecond laser amplifiers.
An economical way to extract semiconducting single-walled carbon nanotubes from common single-walled carbon nanotubes by the liquid-phase exfoliation method was demonstrated. Using the extracted samples as a saturable absorber, a passively Q-switched Nd : YVO4 laser was realized, delivering a pulse duration of 83 ns at a repetition rate of 290 kHz, resulting in a maximum peak power of 1.3 W. Such an outstanding saturable absorption might be caused by high diameter concordance and semi-conducting property.
An efficient soliton mode-locking femtosecond Yb3 + : Y2SiO5 (Yb:YSO) laser at 1059 nm assisted with semiconductor saturable absorber mirror has been successfully realized and demonstrated. Nearly Fourier transform-limited pulse duration as short as 236 fs has been achieved with a pulse repetition frequency of 79.6 MHz and an average output power of 903 mW, corresponding to maximum pulse energy of 11.34 nJ and pulse peak power of 48 kW, respectively. The dependence of pulse duration on the intracavity pulse energy in soliton mode-locking regime has been further investigated and discussed, which is fitted by the soliton mode-locking theory and indicates the nonlinear refractive index n2 of the Yb:YSO crystal to be around 2.1 to 4.8 × 10 − 16 cm2 / W.
First principles calculations based on the plane wave pseudo-potential method have been carried out to study effects of intrinsic point effects in GaAs saturable absorbers on the related electronic structures and optical properties. The defect energy levels corresponding to each kind of the intrinsic point defect and their electron occupancy are analyzed from the aspects of band structure and partial density of states (PDOS). Furthermore, the impacts on the optical properties of GaAs saturable absorbers made by the native point defects are also obtained. It can be found that the absorption edges of the GaAs with VGa defect, VAs defect or GaAs defect exhibit substantial redshifts, which is mainly attributed to the defect energy levels in the band gap, and the absorption coefficient of the GaAs crystal with VGa defect, VAs defect or GaAs defect is bigger than those with other defects in near-infrared range. The dielectric function and the refractive index of GaAs crystal with VGa defect, VAs defect or GaAs defect show redshifts in near-infrared region too. The analysis of the optical properties of GaAs crystal with intrinsic point defects will be helpful in guiding the application of the GaAs crystal as saturable absorber in solid-state laser.
First-principles calculations are performed for the effects of the intrinsic defects in GaAs saturable absorber, using the
state-of-the-art computational method with the Heyd-Scuseria-Ernzerhof (HSE) hybrid functional to correct the band gap.
The defect energy levels corresponding to all point defects and their electrical characteristics are analyzed from the aspects
of density of states and band structures. Furthermore, the partial band decomposed charge density of the defect bands are
also been studied. The relationships between defect energy levels and EL2 deep-level defect will be helpful in ascertaining
the origin of the EL2 deep-level defect in GaAs.
By considering the influence of the turn-off time and the modulation frequency of the acousto-optic (AO) modulator, the coupled rate equations for a diode-pumped doubly Q-switched and mode-locked (QML) laser with AO modulator and Cr4+∶YAG saturable absorber under Gaussian approximation are given. By numerically solving these equations, the key parameters of an optimally coupled doubly QML laser including the gain medium, the saturable absorber and the resonator as well as the modulation frequency of AO modulator are obtained, which can maximize the pulse energy of singly Q-switched envelope. A diode-pumped doubly QML Nd∶GdVO4 laser with AO modulator and Cr4+∶YAG saturable absorber is constructed and the experimental results are in agreement with the numerical simulations.
A simultaneous Q-switched and mode-locked (QML) Nd:LuVO4 laser with an acousto-optic (AO) modulator and GaAs was presented. By inserting an AO modulator into the laser cavity, the stability of the QML pulses was improved and the pulse width was compressed significantly. The pulse energy and the peak power of mode-locked pulses under the Q-switched envelope had greatly increased. Considering the influences of the turnoff time and the modulation frequency of the AO modulator, a rate equation model for dual-loss modulated QML lasers was given and the numerical solutions of the rate equations were in good agreement with the experimental results.
Using the ABCD matrix theory that takes into account the thermal lens effect of the gain medium and rate equations that consider the Gaussian spatial distributions of the intracavity photon density and pump beam, the pulse duration of a passively Q-switched laser is optimized by choosing the appropriate oscillating beam radius on the Q-switch wafer and pump beam radius in the gain medium, which provides a simple way to optimize the pulse duration. By changing the positions of the GaAs in the cavity or the pump beam focal plane in the gain medium in a diode-pumped passively Q-switched Nd:YVO4 laser with a GaAs saturable absorber, the optimization of pulse duration is easily realized, which is in good agreement with the theoretical calculations.
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 laser-diode-pumped, doubly Q-switched, intracavity optical parametric oscillator (IOPO) with both acousto-optic modulator (AO) and Cr4+:YAG saturable absorber 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 into account the equations. In the experiment, a laser-diode-pumped, doubly Q-switched, Nd:YVO4/KTP IOPO with an acousto-optic (AO) modulator and a Cr:YAG saturable absorber is realized. The shortest pulse width of 6.7 ns has been obtained at the maximum pump power of 6.3 W. The experimental results agree well with the theoretical calculations.
By using both GaAs and Cr4+:YAG saturable absorbers simultaneously in the same cavity, a xenon-flash-lamp-pumped doubly passively Q-switched intracavity-frequency-doubling Nd3+:YAG/KTP green laser is realized. This laser can generate a more symmetric shape and shorter pulse width compared to the solely passively Q-switched intracavity-frequency-doubling green laser with Cr4+:YAG or GaAs saturable absorber. A symmetric factor is defined to describe the temporal symmetry of the pulses quantitatively. The coupled rate equations under the plane-wave approximation are used to simulate the Q-switched process of the laser, and the numerical solutions agree well with the experimental results.
A model based on rate equations that consider the spatial distribution of photon density and inversion population density, as well as the turnoff time of an acoustic-optical modulator, is developed to perform accurate predictions of the characteristics of a green laser. Numerical solutions are consistent with the experimental results of a diode-pumped acousto optical Q-switched intracavity-frequency-doubled Nd:GdVO4/KTP green laser.
By considering the Gaussian spatial distribution of the intracavity photon density, we introduce the rate equations of a diode-pumped Nd:YVO4 laser doubly Q-switched by an acousto-optic modulator and a Cr4+:YAG saturable absorber. These rate equations are solved numerically, and the dependences of pulse width on incident pump power at different pulse repetition rates are obtained. It is shown that the pulse width is obviously compressed in contrast to a diode-pumped actively Q-switched laser with an acousto-optic modulator and the numerical solutions are in agreement with the experimental results performed by a diode-pumped doubly Q-switched Nd:YVO4 laser with acousto-optic Cr4+:YAG.
The intracavity photon density and the initial population-inversion density are assumed to be Gaussian spatial distributions in the rate equations of a laser diode end-pumped passively Q-switched Nd:YVO4 laser with Cr4+:YAG saturable absorber. These space-dependent rate equations are solved numerically. In an experiment, such a laser has been realized. The dependences of pulse width, pulse repetition rate, single-pulse energy, and peak power on incident pump power were measured, and the experimental results are consistent with the numerical solutions.
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