Evaluation of a galvanometric scanner for rapid tuning of CO2 lasers

• Published in: Review of scientific instruments 1989-03, Vol.60 (3), p.322-326
• Main Authors: Gautier, Cynthia R., Fox, Jay A., Ahl, Jeffrey L.
• Format: Article
• Language: English
• Subjects: Exact sciences and technology; Fundamental areas of phenomenology (including applications); Gas lasers including excimer and metal-vapor lasers; Lasers; Optics; Physics
• ISSN: 0034-6748; 1089-7623
• DOI: 10.1063/1.1140431

Remote sensing of gaseous constituents in the atmosphere is possible with a single laser system operating at high (more than 100 Hz) pulse tuning rates so as to minimize the effects of atmospheric turbulence. This article investigates the possibility of using a galvanometric scanner as a rapid tuning device for both pulsed and continuous‐wave CO2 lasers. Preliminary cw experiments, performed in anticipation of future heterodyne lidar development, indicated that lines could be switched at rates up to 77 Hz over the entire spectrum, while much greater rates were achieved by restricting the angular displacement of the galvanometer. When used with a transversely excited atmospheric (TEA) laser, the galvanometer was able to switch lines as fast as 140 Hz. However, amplitude‐dependent position adjustments were necessary to compensate for settling time and/or thermal drift effects in order to obtain maximum energy output. A calibration curve was constructed and tested, but predictions of peak energy positions were accurate only for high gain lines. Using a 16‐bit D to A converter with computer control, there was more than adequate resolution available to extract the maximum energy from each line, even at low gain line positions. Only a small amount (250 μrad maximum) of far‐field beam wander was measured during tuning between any two lines at maximum tuning rates. Thus, it appears that tuning a CO2 laser at line switching rates greater than 70 Hz is possible, but requires a feedback mechanism and/or additional sensor for accurate positioning. Although the galvanometer itself is a relatively simple and compact device, practical utilization may require additional equipment or algorithms.