D. T. Hodges

Efficient high-power operation of the cw far-infrared waveguide laser

Order‐of‐magnitude increases in output power and efficiency have been obtained from optically pumped FIR lasers using a new FIR waveguide laser geometry and a new output coupler. Conversion efficiencies 5–15% of the theoretical maximum are reported for several lines between 71 and 1222 μm and cw output of 400 mW at 118 μm and 40 mW at 496 μm are obtained from a laser 2 m in length. These results indicate that the stronger FIR transitions are capable of cw operation at the 0.1–1.0‐W level for 100 W of CO2 pump power.

Far infrared imagery

Active imaging experiments are described in the 300 microm-l mm-region of the far infrared (FIR) spectrum. Transmission data are presented for a wide variety of common materials indicating the range of applicability of FIR imaging to law enforcement or nondestructive testing. The FIR images of several objects are presented, and the practicality of FIR imaging is discussed in light of straightforward improvements that can be made in the simple imaging system employed in these studies.

A review of advances in optically pumped far-infrared lasers

Abstract This paper reviews the general operating principles and techniques that have evolved from research during the past several years on pulsed and CW optically pumped rotational transition lasers. State-of-the-art performance is summarized and discussed in terms of output expectations estimated from simple rate equation modeling. The impact of molecular dynamics on laser design and geometric configuration is considered along with speculation on future trends.

High-power operation and scaling behavior of CW optically pumped FIR waveguide lasers

High-power far infrared (FIR) laser operation at the 10- 100 mW level is described for wavelengths throughout the 40 μm-1.22 mm spectral region. These data correspond to order of magnitude improvements in converting CO 2 laser energy into FIR laser output. This improved FIR laser performance is attributed to a waveguide laser geometry with reduced losses for the CO 2 pump and also to a new method of output coupling. The basic design concept of the efficient laser resonator is discussed as well as the prospect for further increases in laser performance through improved efficiency and sealing.

Basic physical mechanisms determining performance of the CH3F laser

Abstract This paper summarizes the results of a series of diagnostic experiments which clarify the basic physical mechanisms of the CH 3 F laser. Theoretical predictions of laser performance are compared with experimental data.

Low-threshold CW submillimeter- and millimeter-wave laser action in CO 2 -1aser-pumped C 2 H 2 F 2 , and CH 3 OH

Abstract : CW laser action between 40.7 micrometers and 1.02 mm is described in 1, 1 difluoroethane, 1, 1 difluoroethylene, and methyl alcohol optically pumped by a CO2 laser. Far infrared radiation (FIR) laser threshold was achieved for CO2 pump powers of typically 1 to 2 watts, and FIR laser output powers of several milliwatts were observed on the stronger lines. (Modified author abstract)

High performance at new FIR wavelengths from optically pumped CH 2 F 2

A parametric study to clarify efficiency limiting mechanisms and to maximize the performance of the CH(2)F(2) laser has led to the discovery of five new CO(2) pump lines and ten new FIR laser lines. The wavelengths of the new lines fill a previous gap in the spectrum of strong cw FIR laser lines. With appropriate cavity design, measured conversion efficiencies exceed 30% of the maximum theoretical limit. Optimization of the output coupling for the strongest line at lambda = 184.6 microm has doubled the maximum output power from the identical system using the lambda = 118.8-microum line of CH(3)OH. The exceptionally high conversion efficiency (33%) occurring at the highest-available CO(2) pump power indicates that the limits on scaling to higher output powers have not yet been reached. The results confirm the high-performance capability of the CH(2)F(2) laser, the strongest cw optically pumped FIR laser reported to date.

Extension of the Schottky barrier detector to 70 μm (4.3 THz) using submicron‐dimensional contacts

Schottky barrier diode detection in both video and mixing modes of operation has been extended to 4.252 THz (70.5 μm) using 0.5‐μm‐diam diodes fabricated from heavily doped nonepitaxial n‐type GaAs. These ultrasmall, and consequently ultralow capacitance, junctions were prepared using electron‐beam lithography and have yielded the smallest reported series‐resistance junction‐capacitance product for a Schottky barrier diode. The potential for extending diode operation to still higher frequencies is discussed.

High-Resolution Atmospheric-Transmission Measurement Using a Laser Heterodyne Radiometer

Knowledge of the atmospheric transmission precisely at laser emission wavelengths is very important in many laser experiments. Over horizontal propagation paths a direct measurement of the transmission using the laser source can be made. A vertical propagation path through the entire atmosphere presents a more difficult measurement problem at the requisite spectral resolution. At present, the most reliable transmission coefficients are calculated using atmospheric models. It is the purpose of this letter to show that a laser heterodyne radiometer can be used to measure accurately the atmospheric transmission for laser radiation propagating through the entire atmosphere. Measurements, with a spectral resolution of 7 × 1 0 4 c m 1 , are presented for the P(20) C O2 1 6 laser line and compared with the calculated values. In a recent article, McElroy has discussed the use of a laser radiometer receiving solar radiation for measuring the atmospheric transmission and for making solar temperature measurements. He indicates that an adequate signal-to-noise ratio can be achieved by chopping the incident radiation and synchronously detecting the heterodyne signal. In the present work, the emphasis is on the measurement of the atmospheric transmission coefficient close to the center of the CO2 gaseous absorption line. For this purpose the spectral bandwidth must be small and, consequently, the signal-to-noise ratio is not excessive. Our expression for the postdetection signal-to-noise ratio differs slightly from that of McElroy because we chose a different postdetection correlation (sinusoidal modulation and correlation) and included a geometric factor χ. The factor χ, which is unity for an extended source and is less than unity for a finite source, has been calculated by Yura as a function of the detector size and Fig. 1. Block diagram of the laser heterodyne radiometer.

New far infrared CW optically pumped cis-C 2 H 2 F 2 laser

Lasing on 6 FIR lines is reported for the new laser molecule cis-C2H2F2with high conversion efficiencies up to 7 percent of the maximum theoretical limit. A set of molecular selection criteria was used to predict efficient FIR lasing from this molecule, and analysis of the laser performance has increased the basic understanding of the molecular parameter contribution to high conversion efficiency. From this work a refined set of selection criteria has evolved that may be used to predict additional efficient laser molecules.