Browse Prior Art Database

Cross Field Nitrogen Laser With Gas Introduction to Form a Shock Wave

IP.com Disclosure Number: IPCOM000086970D
Original Publication Date: 1976-Nov-01
Included in the Prior Art Database: 2005-Mar-03
Document File: 4 page(s) / 71K

Publishing Venue

IBM

Related People

Dreyfus, RW: AUTHOR

Abstract

Nitrogen lasers are commonly constructed with a fast, high current source passing electrical current through the nitrogen at ~50 torr pressure. For the present purpose, the high current source is a Blumlein transmission line, although N(2) lasers with discrete coaxial feedpoints behave quite similarly. In either case, the ability to convert electrical energy into excited N(2) molecules is limited because the electrical impedance of the N(2) gas drops to a very much lower value than the characteristic impedance (~0.1 ohm) of the Blumlein during the time of the discharge. Also, at times >/~0.1 nsec, the electron temperature drops to too low a value (

This text was extracted from a PDF file.
At least one non-text object (such as an image or picture) has been suppressed.
This is the abbreviated version, containing approximately 53% of the total text.

Page 1 of 4

Cross Field Nitrogen Laser With Gas Introduction to Form a Shock Wave

Nitrogen lasers are commonly constructed with a fast, high current source passing electrical current through the nitrogen at ~50 torr pressure. For the present purpose, the high current source is a Blumlein transmission line, although N(2) lasers with discrete coaxial feedpoints behave quite similarly. In either case, the ability to convert electrical energy into excited N(2) molecules is limited because the electrical impedance of the N(2) gas drops to a very much lower value than the characteristic impedance (~0.1 ohm) of the Blumlein during the time of the discharge. Also, at times >/~0.1 nsec, the electron temperature drops to too low a value (</~5eV).

In the following description and in Fig. 1, an apparatus is described which overcomes these limitations by dynamically introducing the N(2) gas so as to produce a pressure gradient. The general concept and relative timing of the events are shown in Fig. 2.

Prior to firing, the Blumlein is charged to ~20 kV and the laser tube is evacuated to a pressure <<1 torr. At time t=0, a solenoid valve is rapidly opened to introduce the N through an aperture in one of the electrodes and starts across the discharge channel. A shock wave forms a sharp boundary between the high density N(2) gas introduced into the chamber and the low density gas ambient in the chamber. After the high pressure (~50 torr) N(2) gas has traversed approximately half the width of the laser tube, the Blumlein discharge circuit is activated by switch S. The electrical discharge requires <<10 nsec, so that the N(2) gas may be considered as stationary during this time.

The average electrical impedance during the discharge time is adjusted to equal or slightly exceed the impedance of the Blumlein. The impedance is increased by decreasing the gas density on the low pressure side of the shock front. Under the condition of nearly matched impedances, a current of ~10/5/ amperes will flow in the discharge, corresponding to an excitation power of ~10/9/ watts. If an electrical to laser efficiency of about .3% is assumed, the nitrogen laser power is 3M watts. The efficiency should be high because the electrons will cross over into the high density N(2) with energies of >>10eV. The maximum kinetic energy that the electrons could have is 20kV which would produce a range of ~1 cm in 50 torr...