R.A. Wood

An optically pumped waveguide laser with mesh reflectors

Abstract An optically pumped far infrared waveguide laser has been operated using metallic meshes as laser reflectors. The radiation modes sustained in the waveguide laser have been examined, and the use of the laser for magneto-optical measurements demonstrated.

Stimulated spin-flip Raman scattering: a magnetically tunable infrared laser. I

A microscopic theory of spin-flip Raman scattering from conduction electrons in semiconductors has been set out both in terms of appropriate general scattering theory and of detailed calculation of the electron band states of a solid in a magnetic field. From the latter, matrix elements determining the scattering cross-section have been evaluated as a function of frequency and magnetic field for the various ‘anharmonic’ processes involved in indium antimonide. New experimental results on magnetic field dependence of gain and loss, of direct relevance to comparison with microscopic theory, are presented and discussed. These results, together with earlier work, confirm the basic theoretical model and clearly demonstrate the potential of this continuously tunable infrared laser.

Spectroscopy between 5 and 6 μm with a tunable spin-flip Raman source

Abstract We describe the application of a tunable, infrared, spin-flip Raman source to the measurement of the absorption spectra of gases in the spectral region 5–6 μm. Continuous tuning was obtained by using a low finesse Raman crystal cavity to eliminate mode pulling and hopping effects. The effects of atmospheric absorption, and pulse-to-pulse and magnetic field dependent intensity variations were cancelled by using a double beam arrangement. As an illustration of the operation of such a Raman spectrometer we obtain the P and Q branch absorption spectra of nitric oxide at various gas pressures in the spectral region 1890-1835 cm -1 . Studies at low gas pressure and with the tunable source operating close to the threshold for stimulated emission show a resolution of ≈ 0.08 cm -1 , determined by the linewidth of the Raman scattered radiation. This linewidth is shown to be in agreement with a mechanism of stimulated superradiant narrowing of the spontaneously scattered lineshape.

Mode properties of optically pumped infrared waveguide lasers

Abstract An optically pumped CF3OH far i.r. waveguide laser has been operated using metallic meshes as laser reflectors. The radiation modes sustained in metal and glass waveguides have been examined, and the use of the laser for magneto-optical measurements demonstrated.

Tunable far-infrared generation by difference frequency mixing in InSb

Abstract Far-infrared radiation tunable over the range 85–105 cm -1 and at power levels of up to 10 μW has been generated by difference frequency mixing in InSb. The infra-red radiations which are mixed are a 10.6 μm TEA-CO 2 laser line and the tunable Stokes radiation produced from it by spin-flip Raman-laser action, again in an InSb sample. It is argued that careful choice of the free-carrier concentrations in the crystals used for (a) the Stokes generation and (b) the mixing, or the application of an electric field across the mixing sample, should considerably improve the far-infrared power levels.

Tunable laser-sideband generation in InSb

Abstract The resonant third order non-linear susceptability in InSb has been employed to generate a magnetically tunable cw laser sideband near 5 μm.

Operating characterics of an optically pumped waveguide fir laser

Abstract We report measurements of the effect of resonator length changes, 13 CO 2 laser frequency and 13 CO 2 laser intensity on the FIR power emitted by an optically pumped waveguide FIR laser operating on the exceptionally strong 15 NH 3 laser line at 152.9 μm. The Doppler-splitting of the FIR output frequency shows a CO 2 power-dependent deviation from the linear dependence on 13 CO 2 laser frequency expected from rate equation theory. Similar, but weaker, effects are also reported using the less strong CH 3 OH FIR line at 118.8 μm.

High power pulsed operation of a tunable spin-flip raman laser at low magnetic field

Abstract We report high power (kW), high efficiency (40%) operation of a pulsed tunable spin-flip Raman laser near 5.3 μm, with magnetic fields as low as 0.9 kG. Continuous tuning over a range of 52 cm -1 with radiation linewidths of 2 X 10 -2 cm -1 has been obtained using a low field (7kG) electromagnet.

Quantum oscillations and pump depletion effects in an efficient high-power tunable spin-flip laser

Tunable stimulated Stokes, second-Stokes and anti-Stokes Raman scattering have been studied in InSb pumped with short pulses of 5.3 mu m radiation. Very high power levels (700 W) and conversion efficiencies (45%) have been observed for the tunable Stokes emission, and confirmed by measurements of the power depletion of the pump radiation. Stimulated Stokes emission was observed at magnetic fields as low as 5 kG, well below the quantum limit condition, and exhibited a low-field oscillatory variation of the power output due to stimulated spin-flip transitions between high-quantum-number Landau levels.

Fundamental loss mechanisms of the spin-flip Raman laser

The authors have observed striking minima in the spectrum of the output power against magnetic field of the InSb spin-flip Raman laser near 10.6 mu m. These minima, which occur in the Stokes, anit-Stokes and double Stokes emissions, are attributed to harmonic cyclotron resonance absorption of the Stokes scattered radiation in the InSb crystal. Independent studies of the transmission of the sample as a function of magnetic field support this interpretation.