Sourabh Mukhopadhyay

Enhancement of stability and efficiency of a nonlinear mirror mode-locked Nd:YVO(4) oscillator by an active Q-switch.

The stability and the peak power of a nonlinear-mirror mode-locked Nd:YVO(4) laser are significantly increased by the insertion of an acousto-optic modulator inside the laser cavity. The repetition rate for reliable operation can be varied in the range 35 kHz - 50 kHz. The laser generates the most intense and stable mode-locked pulses of width 9 ps lying underneath a Q-switched envelope of width 110 ns with a Q-switch modulation frequency of 38 kHz. For 10 W of pump power, a 224 times enhancement of peak power over that of cw mode-locking is obtained under reliable Q-switched and mode-locked operation.

Simultaneous multi-wavelength oscillation of Nd laser around 1.3 µm: A potential source for coherent terahertz generation

Simultaneous oscillations of 1318.8nm, 1320.0nm, 1332.6nm, 1335.0nm, 1338.2nm and 1339.0nm in a side, pulsed-diode-laser-array pumped Nd:YAG laser is realized for both free running and Q-switched operation. An average power of 1.1W is obtained for an absorbed pump power of 7.1W with an effective optical slope efficiency of 33%. The difference frequency interactions among these wavelengths may be used to generate radiation in the range 0.13-3.43THz. With the two most intense lines at 1318.8nm and 1338.2nm, it is possible to generate coherent radiation at 3.3THz with numerically estimated peak power of 0.21W in a 1.5mm thick GaSe crystal.

Realization of inverse saturable absorption by intracavity third-harmonic generation for efficient nonlinear mirror mode-locking

A technique of suppressing passive Q-switching by inverse saturable absorption in a cw nonlinear mirror mode-locked laser is presented. The nonlinear mirror saturable absorber consists of a second-harmonic generation crystal and a dichroic mirror while the inverse saturable loss is realized by intracavity third-harmonic generation. The inverse saturation reduces significantly the critical intracavity pulse energy for stable, self-starting, self-sustained, and power scalable cw mode-locking. Two LiB3O5 crystals are employed to realize the technique in a diode array pumped Nd:YVO4 oscillator providing a peak power of 918W, pulse width of 29ps, and repetition rate of 170MHz.

Dual colour cw mode-locking through soft aperture based on second order cascaded nonlinearity

Large nonlinear phase shift achieved by exploiting intracavity second order cascaded nonlinear process in a non-phasematched second harmonic generating crystal is transformed into amplitude modulation through soft aperturing the nonlinear cavity mode variation within the laser gain medium to mode-lock a Nd:YVO4 laser. The laser delivers stable dual wavelength cw mode-locked pulse train with pulse duration 10.3 ps and average power of 1.84 W and 255 mW at 1064 nm and 532 nm respectively for a pump power of 12 W. A comprehensive theoretical analysis finds the regime of self starting and stable cascaded second order mode-locking, inconformity with the experimental result.

Acousto-optic-modulator-stabilized low-threshold mode-locked Nd:YVO4 laser

A substantially low-threshold, kilohertz repetition rate and laser-diode-array pumped Nd:YVO4 laser, actively Q switched by an acousto-optic modulator and passively mode locked by a nonlinear mirror consisting of a KTiOPO4, second harmonic generating crystal, and a dichroic output coupler, is demonstrated with enhanced efficiency. The mode-locked pulses with a width of 11.5ps lie underneath a Q-switched envelope having a width of 58ns with a Q-switched modulation frequency of 40kHz. For 10W of pump power, a peak power of 719kW is obtained under stable Q-switched and mode-locked operation, which is a marked improvement compared to the earlier reports.

Picosecond pulse generation and its simulation in a nonlinear optical mirror mode-locked laser.

A nonlinear mirror composed of a lithium triborate crystal and a dichroic output coupler is used to passively mode lock an Nd:YVO4 laser that is pumped by a diode laser array. A mode-locked output power of 3.2 W, a repetition rate of 178 MHz, a pulse width of 8.4 ps, and a beam quality parameter (M2) of 1.27 are obtained at 1064 nm for a pump power of 10.0 W. The numerical simulation for the steady-state pulse width agrees well with the bandwidth-limited value. A double-pass average gain g(ave) is defined by considering the constancy of the output energy. In the simulation g(ave) is kept as a free parameter, and its value required for the bandwidth-limited pulse is found to be 0.047, whereas its calculated value, based on our definition, is 0.057.

Diode array pumped, non-linear mirror Q-switched and mode-locked Nd : YVO4 laser — a good tool for powder SHG measurement

A non-linear mirror consisting of a lithium triborate crystal and a dichroic output coupler are used to mode-lock (passively) an Nd : YVO4 laser, pumped by a diode laser array. The laser can operate both in cw mode-locked and simultaneously Q-switched and mode-locked (QML) regime. The peak power of the laser while operating in QML regime is much higher but pulses suffers from poor amplitude stability. The incorporation of an acousto-optic modulator as an active Q-switch enhances the stability of the QML pulse envelope. The second-order non-linearity of powdered crystalline urea is conclusively measured with respect to KDP while the laser is operating in passively Q-switched and passively mode-locked regime as well as in actively Q-switched and passively mode-locked regime.

Widely Tunable Intracavity Phasematched Cascaded Second-Order Interaction for the Generation of Multicolor Radiation

A theoretical and experimental study of all-solid-state barium borate (BBO)-based optical parametric oscillator with wide tunability from visible to near-infrared by means of intracavity second-order cascaded nonlinear interaction has been demonstrated for simultaneous generation of multicolor radiation. Radiations in the wavelength range of 600-661 nm in the visible and 892-1322 nm in the near-infrared range are generated by a combination of optical parametric oscillation and simultaneous second harmonic generation in BBO crystal. The effective third-order susceptibility is measured to be 885.18 pm2/V2, which is greater than intrinsic third-order susceptibility by one order of magnitude.

Intracavity cascaded second order interaction in BBO for generation of efficient, widely tunable coherent radiation

An all-solid-state BBO-based widely tunable coherent source from visible to near-infrared source is developed by means of intra-cavity second-order cascaded nonlinear interaction with

Multi-colour OPO based on second order cascaded nonlinear interaction

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