Date of Award

Spring 2000

Document Type

Thesis

Degree Name

Master of Science (MS)

Department

Electrical & Computer Engineering

Program/Concentration

Electrical Engineering

Committee Director

Amin N. Dharamsi

Committee Member

Karl H. Schoenbach

Committee Member

Ravindra P. Joshi

Call Number for Print

Special Collections LD4331.E55 F58

Abstract

Wavelength modulation spectroscopy was employed to investigate water vapor absorption lines in the 1.462 µm wavelength region using an external-cavity diode laser. These measurements were necessary in the development of a lidar (light detection and ranging) instrument for differential absorption measurement of the concentration and movement of water vapor in the Earth's atmosphere. Differential absorption measurements require that the laser frequency remain stable throughout the duration of the measurement. To ensure this stability, the laser output wavelength is monitored and a feedback control loop set up to minimize laser line drift. Three lines were investigated in the 1.462 µm region. The first-harmonic spectroscopic signal of the strongest of these lines was used as an error signal for the stabilization feedback loop. The derivative-like nature of harmonic signals provides a zero crossing for odd harmonics, which can be used to determine the polarity of the requisite feedback voltage and compensate the laser wavelength accordingly. The feedback control loop utilized the virtual instrument capabilities of Labview and locking to within ±5.2MHz was achieved using this method. The feedback loop was also tested on two other lasers to demonstrate flexibility. These lasers, and external cavity diode laser centered at 944nm and a Ho:Tm:YLF laser, will also be used in the development of lidar instruments for the measurement of atmospheric water vapor. The Ho:Tm:YLF laser can be used to measure carbon dioxide as well.

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DOI

10.25777/jnrx-0z19

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