Plasma shutter for pulse shaping of TEA CO 2 laser

Abstract

Two types of plasma shutters which can achieve pulse shaping of transversely excited atmospheric-pressure (TEA) Co2 laser are presented. We have designed two optical devices, which are plasma shutter and laser triggering spark gas (LTSG). The pulse forming network circuit used for precise triggering control is designed. In experiment, optical triggering gas free-breakdown plasma shutter and electrical triggering plasma shutter controlled via LTSG are researched for pulse shaping of the TEA CO2 laser. The collimated laser beam is focused at the center of two ZnSe lenses, producing an intensity of approximately 7x 1O'°W/cm2. In order to optimize truncated laser pulses, some operating parameters which include gas types filled in plasma shutter, gas pressure, LTSG 's voltage, and so on, are investigated via experiments. Using this technique, the nitrogen "tail" of the TEA CO2 laser pulse can be clipped, thus shortening the output laser pulse from the duration 6Ons to '3Ons.

Pulse shaping of transversely excited atmospheric CO2 laser using a simple plasma shutter

“…Several methods have previously been employed to remove the long tail of the pulsed CO 2 laser, including Q-switching 5 and the breakdown plasma shutter. [6][7][8][9][10] The crystal used for Q-switching of CO 2 infrared laser pulses usually absorbs a large portion of CO 2 energy, hence amplifier stages are necessary for obtaining high peak power. 5 Instead, by using a plasma shutter, one can truncate the laser pulse at a certain point in time so as to transmit the high-power initial spike and block the low-power nitrogen tail, therefore increasing the average power of the laser pulse.…”

“…These methods may be combined, for example, electrodes may be placed in a chamber with a pressurized gas. 10 In this manner, breakdown occurs due to electrical discharge, but is facilitated by the pressurized gas in the chamber. This design requires a pressure chamber as well as a timing generator and high-voltage electrical pulse generator.…”

CO2-Tea pulse clipping using pulsed high voltage preionization for high spatial resolution I.R. Lidar systems

“…For helium and argon, the threshold intensities extend from 3×10 11 Wcm −2 -5×10 12 Wcm −2 and from 2×10 11 Wcm −2 -2×10 12 Wcm −2 , respectively. The plot shows no evidence for the plateau that illustrates the multiphoton ionization (MPI) processes in gases [3] but does confirms the predominance of the collision ionization process due to the IR emission band of TEA-CO 2 lasers where the laser-induced breakdown is expected to be driven by an avalanche ionization mechanism [4]. For nitrogen, the threshold breakdown intensities extend from 3×10 13 Wcm −2 -2×10 14…”

“…This type of pulse limits the range resolution of LIDARS to some hundreds of meters unless pulsedeconvolution techniques [1] are adopted. Short laser pulses can also be obtained by various techniques such as mode locking, free induction decay, pulse slicing with electro-optic switched [2][3][4][5]. However, output pulses from these require further amplification for any useful application due to their very low energy content.…”