Charles Freed

Determination of laser line frequencies and vibrational-rotational constants of the 12C18O2, 13C16O2, and 13C18O2 isotopes from measurements of CW beat frequencies with fast HgCdTe photodiodes and microwave frequency counters

Abstract The frequencies of 12 C 18 O 2 , 13 C 16 O 2 , and 13 C 18 O 2 isotope lasers have been measured to better than 3 MHz (0.0001 cm −1 ) by comparing with a 12 C 16 O 2 reference laser. Heterodyne techniques were used to generate 139 difference frequencies in a liquid nitrogen cooled HgCdTe photodiode. Microwave frequency counter measurements of the difference frequencies were then used to calculate new values for the band centers and rotational constants of the rare isotopes. Procedures to achieve further improvements are discussed.

ERRATA: STANDING WAVE SATURATION RESONANCES IN THE CO2 10.6‐μ TRANSITIONS OBSERVED IN A LOW‐PRESSURE ROOM‐TEMPERATURE ABSORBER GAS

The standing‐wave saturation resonances are observed by subjecting the CO2 absorber gas to the standing‐wave 10.6‐μ laser field and detecting the change induced in the entire 4.3‐μ (001) → (000) spontaneous emission band as the laser frequency is tuned within the Doppler profile of a specific 10.6‐μ transition. Long‐term stabilization on any oscillating transition is achieved.

OPTICAL HETERODYNE DETECTION AT 10.6 μm OF THE BEAT FREQUENCY BETWEEN A TUNABLE Pb0.88Sn0.12Te DIODE LASER AND A CO2 GAS LASER

Optical heterodyning between a CO2 gas laser and a current‐tunable Pb0.88Sn0.12Te diode laser has been observed with both lasers in CW operation. The beat frequency was tunable from under 50 MHz to 1300 MHz and from 300 MHz to 3500 MHz for heterodyne experiments with the P20 and P18 CO2 laser transitions, respectively.

SEALED‐OFF OPERATION OF STABLE CO LASERS

Several watts of stable (Δf/f≤3×10−10) pure TEM00q‐mode output power was obtained from completely sealed‐off CO lasers at operating temperatures between +35 and −90°C. No deterioration of output powers has been seen after hundreds of hours of sealed‐off operation.

Advances in CO2 Laser Stabilization Using the 4.3 μm Fluorescence Technique

Significant improvement in signal-to-noise ratios is achieved with new, low pressure CO2 stabilization cells external to the lasers. A time domain fractional frequency stability of σy(τ) 6 × 10-12 τ-1/2 was measured with independently line-center locked 1.5 metre grating controlled CO2 lasers. Accurate, repeatable determination of pressure shift is demonstrated.

Fundamental linewidth in solitary, ultranarrow output PbS1−xSex diode lasers

The fundamental, quantum phase noise limited Lorentzian linewidth was directly measured from the beat‐note spectra generated by heterodyning PbS1−xSex diode lasers with a stable CO gas laser. The experimental results were matched by calculated theoretical line profiles. Linewidths as narrow as 22 kHz full width at half‐maximum power were observed.

HgCdTe varactor photodiode detection of cw CO2 laser beats beyond 60 GHz

The simultaneous operation of a HgCdTe photodiode as an optical heterodyne receiver and a varactor microwave harmonic generator and frequency downconverter has made possible the detection of CO2 laser beats to beyond 60 GHz.

Laser radar component technology

The development of the laser soon led to recognition of its potential in radar applications. As radar systems were designed and implemented, however, it became clear that major refinement of the laser sources was needed to meet specific radar transmitter requirements in terms of waveforms, spectral purity, stability, beam quality, and power. The sensitivity and bandwidth of receivers were also in some cases insufficient, and new enabling detector technologies had to be created. This article provides a framework for much of the component development by describing the wideband high-power carbon dioxide (CO/sub 2/) imaging radar system at the Firepond Laser Radar Research Facility. The paper also details the critical components developed for the Firepond CO/sub 2/ range-Doppler imaging laser radar transmitter as well as transmitters for short-range CO/sub 2/ radars.

Absolute frequency calibration of the CO 2 isotope laser transitions

The frequencies of rare CO2 isotope lasers are measured by comparison with 12C16O2 reference lines and with each other. Improved heterodyne techniques are used to generate difference frequencies in a liquid-nitrogen-cooled HgCdTe varactor photodiode. Microwave frequency counter measurements of the difference frequencies are then used to calculate the band centers, rotational constants and transition frequencies with an estimated accuracy of less than a few kilohertz. Selected applications of CO2 isotope lasers in precision heterodyne calibration, spectroscopy, microwave and IR synthesis are described.

Precision Heterodyne Calibration

The frequencies of 12C18O2, 13C16O2 and 13C18O2 isotope lasers have been measured to better than 3 MHz (0.0001 cm−1) by comparison with a 12C16O2 reference laser. Heterodyne techniques were used to generate 139 difference frequencies in a liquid-nitrogen cooled HgCdTe photodiode. Microwave frequency counter measurements of the difference frequencies were then used to calculate new values for the band centers and rotational constants of the rare isotopes. It is shown that an additional thousandfold improvement in accuracy and a greatly extended spectral range can be readily achieved.