Interferometry of resonator modes in submillimeter wave lasers

Characterizing Far-infrared Laser Emissions and the Measurement of Their Frequencies

The generation and subsequent measurement of far-infrared radiation has found numerous applications in high-resolution spectroscopy, radio astronomy, and Terahertz imaging. For about 45 years, the generation of coherent, far-infrared radiation has been accomplished using the optically pumped molecular laser. Once far-infrared laser radiation is detected, the frequencies of these laser emissions are measured using a three-laser heterodyne technique. With this technique, the unknown frequency from the optically pumped molecular laser is mixed with the difference frequency between two stabilized, infrared reference frequencies. These reference frequencies are generated by independent carbon dioxide lasers, each stabilized using the fluorescence signal from an external, low pressure reference cell. The resulting beat between the known and unknown laser frequencies is monitored by a metal-insulator-metal point contact diode detector whose output is observed on a spectrum analyzer. The beat frequency between these laser emissions is subsequently measured and combined with the known reference frequencies to extrapolate the unknown far-infrared laser frequency. The resulting one-sigma fractional uncertainty for laser frequencies measured with this technique is ± 5 parts in 10(7). Accurately determining the frequency of far-infrared laser emissions is critical as they are often used as a reference for other measurements, as in the high-resolution spectroscopic investigations of free radicals using laser magnetic resonance. As part of this investigation, difluoromethane, CH2F2, was used as the far-infrared laser medium. In all, eight far-infrared laser frequencies were measured for the first time with frequencies ranging from 0.359 to 1.273 THz. Three of these laser emissions were discovered during this investigation and are reported with their optimal operating pressure, polarization with respect to the CO2 pump laser, and strength.

Simultaneous measurement of circular dichroism and Faraday rotation at terahertz frequencies utilizing electric field sensitive detection via polarization modulation

A far-infrared system measures the full complex Faraday angle, the rotation as well as the ellipticity, with an unprecedented accuracy of 10 microrad/T. The system operates on several far-infrared laser lines in the spectral range from 0.3 to 6 THz and produces results as a continuous function of temperature from 10 to 310 K and applied fields between +/-8 T. Performance of the instrument is demonstrated by measurements on a GaAs two-dimensional electron gas heterostructure and Bi(2)Sr(2)CaCu(2)O(8+x) single crystal.

High Power Pulsed HCN Laser

By optimizing the discharge parameters of a pulsed HCN laser, peak powers up to 1 kW have been obtained with the output radiation predominantly in the lowest transverse mode. The production of discharge impurities at high input power limits the long-term repetitive operation to 450-W output. Details of the variation of power with discharge voltage, repetitive rate, gas composition, and flow rate are given, and suggestions for further increasing the power are made.

Transient Phenomena in the 337-microm Maser

An attempt has been made to Q-switch the w 337 -microm maser, but no large increase in peak power was observed. The gain factors of 337-microm radiation for pulsed and cw discharges have been measured and found to be 70% per meter and 10% per meter, respectively. It has also been shown that the pulsed maser is saturated in normal operation. Multiple pulse emission has been observed with the output delayed by times of the order 750 microsec after the applied electrical pulse.