P D Gupta
Articles written in Sadhana
Volume 26 Issue 6 December 2001 pp 603-611
A second-order autocorrelator for single-shot measurement of ultrashort laser pulse durations has been set up. It is based on recording the spatial profile of non-collinear phase-matched second harmonic generation in a KDP crystal using a CCD camera-framegrabber combination. Performance of the system is described from measurement of 250 femtosecond transform-limited laser pulses from a passively mode-locked, diode pumped Nd:glass laser. It can also be used for measurement of picosecond laser pulses in the multi-shot scanning mode.
Volume 31 Issue 1 February 2006 pp 61-68
A PC-based control software and data acquisition system is developed for an existing commercial microdensitometer (Biomed make model No. SL-2D/1D UV/VIS) to facilitate scanning and analysis of X-ray films. The software is developed in Labview, which includes operation of the microdensitometer in 1D and 2D scans and analysis of spatial or spectral data on X-ray films, such as optical density, intensity and wavelength. It provides a user-friendly Graphical User Interface (GUI) to analyse the scanned data and also store the analysed data/image in popular formats like data in Excel and images in jpeg. It has also on-line calibration facility with standard optical density tablets. The control software and data acquisition system is simple, inexpensive and versatile.
Volume 31 Issue 5 October 2006 pp 613-620
A single-frame X-ray framing camera has been set up for fast imaging of X-ray emissions from pulsed plasma sources. It consists of two parts, viz. an X-ray pin-hole camera using an open-ended microchannel plate (MCP) detector coupled to a CCD camera, and a high voltage short duration gate pulse for the MCP. The camera uses a 10-Μm pin-hole aperture for imaging on the MCP detector with a magnification of 6 X. The high voltage pulser circuit generates a pulse of variable duration from 5 to 30 ns (at 70% of peak amplitude) with variable amplitude from 800 V to 1.25 kV, and is triggered through a laser pulse synchronized with the event to be recorded. The performance of the system has been checked by recording X-ray emission from a laser-produced copper plasma. A reduction factor of ∼ 6.5 is seen in the dark current contribution as the MCP gate pulse is decreased from 250Μs to 5 ns duration.
Volume 32 Issue 3 June 2007 pp 235-242
An electro-magnetic interference noise shielding enclosure for Pockels cells for high speed synchronized switching has been set-up and tested. The shielding effectiveness of the aluminum enclosures housing the Pockels cells and the electronic circuitry has been measured using a high impedance probe and is found to be $\sim 50 dB$. This ensures a noise-free and synchronized electro-optic switching in an
Volume 33 Issue 4 August 2008 pp 443-453
A large aperture disc ampliﬁer has been designed, set-up and characterized for its performance on small signal gain, spatial variation of gain, and thermal recovery time. This ampliﬁer, consisting of three elliptical Nd: phosphate glass discs of size 214 × 114 × 20 mm mounted at Brewster angle and pumped by ten xenon ﬁlled ﬂash lamps of 600 mm arc length, provided a small signal gain of 6 at electrical pump energy of 36 kJ (in a pulse of 450 𝜇s) using an in-house developed dual-polarity capacitor bank based power supply. It was coupled to a high power Nd: phosphate glass laser chain and a maximum output pulse energy exceeding 100 J in a 1·5 ns (FWHM) pulse has been measured. A dry nitrogen gas based cooling system was developed for cooling the glass discs with a thermal recovery time of ∼ 20 minutes.
Volume 36 Issue 3 June 2011 pp 349-355
X-ray lasing through high voltage, high current discharges in gas ﬁlled capillaries has been demonstrated in several laboratories. This method gives highest number of X-ray photons per pulse. The fast varying current and the j x B magnetic force compress the plasma towards the axis forming a hot, dense, line plasma, wherein under appropriate discharge conditions lasing occurs. At Laser Plasma Division, RRCAT, a program on high voltage capillary discharge had been started. The system consists of a 400 kV Marx bank, water line capacitor, spark gap and capillary chamber. The initial results of the emission of intense short soft X-ray pulses (5–10 ns) from the capillary discharge are reported.