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A new optical design of tiled single grating pulse compressor has been proposed, set-up and studied. The parametric space, i.e. the laser beam diameters that can be accommodated in the pulse compressor for the given range of compression lengths, has been calculated and shown to have up to two fold enhancement in comparison to our earlier proposed optical designs. The new optical design of the tiled single grating pulse compressor has an additional advantage of self compensation of various tiling errors like longitudinal and lateral piston, tip and groove density mismatch, compared to the earlier designs. Experiments have been carried out for temporal compression of 650 ps positively chirped laser pulses, at central wavelength 1054 nm, down to ~235 fs in the tiled grating pulse compressor set up with the proposed design. Further, far field studies have been performed to show the desired compensation of the tiling errors takes place in the new compressor.

A simple, sensitive and robust technique is proposed for coherent alignment of tiled grating assembly using wedge plate lateral shearing interferometry. In this technique, two thick glass wedge plates are used to generate interferograms from reflected and diffracted laser beams, from the tiled grating assembly under alignment. This single optical element based interferometric technique is easy to set up, insensitive to the vibrations and provides simultaneous information of both reference as well as error interference patterns, which are used to estimate the alignment errors. Performance of this technique was tested through alignment of two reflective gratings (size 140 mm X 120 mm), with an angular and translation sensitivities of less than 1 μ rad and 50 nm respectively.

In this paper, we report theoretical studies on optimization of a broadband optical parametric amplifier (OPA) with enhanced output stability for chirped pulse amplification. Optimization of various signal, pump, crystal and ambient parameters has been carried out to achieve an output energy fluctuation that is much smaller than the pump fluctuation. Different practical examples of single/multi stage OPAs and single/ multi pass OPAs, operating in many optical cycles and few optical cycles regimes have been considered in our studies. It is shown that apart from several crystal and beam parameter parameters, crystal temperature and inter/ intra crystal losses constitute important parameters which can be varied to achieve stable broadband pulse amplification in an optical parametric amplifier.

Experimental results of a study on the wavelength dependence and the dynamic range of the quadratic response of commercial grade light emitting diodes (LEDs) are reported over a broad spectral range of 680 nm to 1080 nm using ~ 100 fs duration laser pulses from cw mode locked laser oscillator. A large dynamic range of the quadratic response has been demonstrated in a reverse biased LED. The observed dynamic range compares well with that obtained using a biased photomultiplier tube with large internal gain.

A simple technique is presented to generate temporally flat-top shaped laser pulses using electro-optic modulator (Pockels cell). It involves splitting of input laser pulse into two halves of equal intensity and then stacking together with appropriate optical delay to get a temporally flat-top laser pulse. It also allows generation of other pulse shapes by varying the relative intensity, delay, and phase between two halves of the input laser pulse. Temporally flat-top laser pulses of duration ~ 9 ns have been generated using ~ 7 ns duration incident laser pulses from a flash lamp pumped Q-switched Nd:glass laser oscillator. The rise and fall-time of the shaped pulse is limited by speed of electro-optic switch (Pockels cell), which is ~ 2 ns in the present case.

A simple flash lamp pumped Nd:phosphate glass laser oscillator has been designed and set up delivering laser pulses of variable duration from ∼800 ps to 6 ns. It is based on Q-switching and full-wavelength cavity dumping and provides single laser pulse energy of 5 mJ and 11 mJ corresponding to pulse duration of ∼800 ps and 6 ns respectively at an electrical pump energy of 50 J. While the maximum pulse duration is governed by the cavity round trip time, the lower limit is decided by the switching speed of the high voltage pulse to the Pockels cell of the cavity dumper. Output laser pulses have shown enhanced pulse energy stability by dumping the cavity four round trips after the peak buildup. The laser pulses were synchronized with 250 ps positively chirped laser pulse train derived from an independent commercial cw mode locked Nd:fluorophosphate glass laser oscillator. The temporal jitter between these two pulses was measured to be ∼200 ps, limited by the speed of the electronics used.

In this paper, a new method for alignment of the pinhole of a spatial filter (SF) has been proposed and demonstrated experimentally. The effect of the misalignment of the pinhole on the laser beam profiles has been calculated for circular and elliptical Gaussian laser beams. Theoretical computation has been carried out to illustrate the effect of an intensity mask, placed before the focusing lens of the SF, on the spatial beam profile after the pinhole of the SF. It is shown, both theoretically and experimentally, that a simple intensity mask, consisting of a black dot, can be used to visually align the pinhole with a high accuracy of 5% of the pinhole diameter. The accuracy may be further improved using a computer-based image processing algorithm. Finally, the proposed technique has been demonstrated to align a vacuum SF of a compact 40 J Nd:phosphate glass laser system.