B.W. James

Far‐infrared superradiant laser action in methyl fluoride

Submillimeter laser pulses exceeding 1‐MW power have been generated superradiantly in CH3F gas pumped by 200 MW of 9.55‐μ CO2 TEA laser radiation. When far‐infrared output was restricted to operation on the 496 line alone, 0.5 MW was achieved within a bandwidth of 100 MHz.

An experimental study of a CW optically pumped far infrared formic acid vapour laser

Abstract This paper describes a comprehensive experimental study of the performance of an optically pumped formic acid waveguide laser operating at wavelengths of 394, 419, 433 and 513 μm. The variation of output power with Pyrex waveguide diameter, in the range 30–92 mm, and output coupling fraction, between 5 and 40% per double pass, is studied in detail. The results are fitted to a theoretical model to obtain the gain and saturation intensity as a function of tube diameter. For this 1.5m long laser, pumped by a 33 W CO 2 laser, the optimum diameter and output coupling are found to be ~ 50 mm and ~20% respectively. This laser is capable of giving output powers of the order of 50 mW on all four lines. Output coupling is varied by using a range of aluminium strip gratings on fused quartz substrates with Teflon antireflection coatings on their rear surfaces, for which the transmission properties are accurately calculable. The polarising properties of the strip grating couplers are used to measure the polarisation anisotropy of the laser output. For typical operating conditions the ratio of maximum to minimum power is in the range 1.2–1.9 for the four lines studied. Laser resonator interferometry is used to study the pair of lines with wavelenghts close to 433 μm, which are separated by 56 MHz, and to identify the longer wavelength line as the stronger.

Effect of repetition rate of a pulsed microwave diamond forming plasma on the density of C2

The relative density of C2 in a pulsed microwave discharge, used for diamond deposition, was measured by optical emission spectroscopy. It was found that the average density of C2 increases with increasing plasma repetition rate (200 Hz–8 kHz) and approaches a limit at high frequencies. These results are explained with a simple plasma chemical kinetics simulation of the pulsed discharge.

The use of Fourier transform techniques for the analysis of hook interferograms

Abstract Hook interferometry is widely used for the measurement of atomic oscillator strengths and atomic energy level populations. The application of Fourier transform techniques to the analysis of hook interferograms is shown to produce greater precision in the determination of hook separation by either the hook or vernier methods. Result obtained for copper density in a magnetron sputtering discharge are presented.

Polarization switching in a strip grating coupled optically pumped submillimeter laser

It is shown that an optically pumped formic acid laser operating at 394 or 433 μm can lase on two sets of nondegenerate orthogonally polarized modes when a strip grating output coupler is used. The laser output polarization can be switched from parallel to perpendicular to the strips by a small cavity length change which is in accordance with calculated reflection phase changes of the grating for the two polarizations. For 30 W pump power ∼5 mW can be obtained at 394 μm in either polarization when the grating strips are oriented perpendicular to the pump polarization.

Observation of enhanced laser emission and new laser transitions in triple cascade operation of an optically pumped cw HCOOH submillimeter laser

We report an investigation of the enhancement of the output power and the observation of new cw lasing transitions for an optically pumped formic acid laser when the resonator length is adjusted so that it is simultaneously resonant for adjacent rotational cascade transitions. Cascade operation was found to be a particularly useful technique for increasing the power of the second transition of a cascade sequence. New cw transitions were observed at 418 μm (the third member of the 394 μm, 406 μm cascade), 447 μm (the third member of the 419 μm, 432 μm cascade), and 460 μm (the third member of the 433 μm, 446 μm cascade).

Annular slot array output couplers for submillimetre lasers

Abstract Arrays of circular and square slots in a metal layer on a transparent substrate have been used as output couplers for an optically pumped formic acid submillimetre laser. These couplers exhibit narrow bandpass transmission, which by suitable choice of dimensions, can provide optimum reflectance at the laser wavelength while also having very high reflectance at the CO 2 pump wavelength. The use of such couplers in place of strip grating couplers produced a 67% increase in submillimetre output power.

A novel cw optically pumped submillimeter laser

Abstract Laser operation has been achieved in an optically pumped submillimetre laser that employs a novel cw resonator design which separates the pumping optics from the resonator optics by the use of a Brewster window. This design also allows pumping by an unfocused CO 2 laser beam. The preliminary performance characteristics of the laser are presented.

Simultaneous two wavelength operation of an optically pumped HCOOH laser on orthogonally polarized modes

Simultaneous laser operation in orthogonally polarized EH11 and TE01 waveguide modes is reported for pairs of cascade lines from an optically pumped formic acid vapour laser incorporating a strip grating output coupler. Observations were made for the 394 μm/406 μm and 433 μm/446 μm cascade sequences, the resonator length being adjusted so that the laser was simultaneously resonant on a mode of the primary transition polarized perpendicular to the strips of the output coupler and the same transverse mode of the secondary transition polarized parallel to the coupler strips. Power measurements showed that for the laser configuration used in this study the power of the primary transition was increased only slightly when the cascade lines were simultaneously resonant, whereas the secondary line could only lase under these conditions.

Resonant array input couplers for optically pumped FIR lasers

Abstract An input coupler consisting of an array of conducting rings on a ZnSe substrate has been used in an optically pumped formic acid laser operating at 433 μm. By using a uniform pump beam of optimized diameter a higher conversion efficiency than obtainable with hole input coupling has been achieved.