V. T. Nguyen

Spin‐flip Raman laser at wavelengths up to 16.8 μm

An InSb spin‐flip Raman (SFR) laser is pumped with an optically pumped NH3 laser line at 780.515 cm−1 to obtain tunable first Stokes laser radiation at wavelengths up to 16.8 μm. We report results on the power output, tunability, and preliminary spectroscopy of UF6. Scaling of the primary CO2 pump laser as well as the NH3 laser together with the SFR laser appears possible for potential application of this system to uranium isotope separation.

Spin dynamics and four-photon mixing in InSb

Abstract The spin flip Raman interaction can be used to excite coherent spin precession in semiconductors. Resonant, four-photon mixing is shown to be equivalent to Raman scattering from this coherent state. Studies of the four-photon intensity give information concerning spin dynamics (T1 and T2) in n-InSb.

Tunable cw difference‐frequency generation in tellurium at ∼11 μm

The narrow spectral width and the nearly continuous tunability of the cw spin flip Raman (SFR) laser operating near 5.3 μm can be transferred to other wavelengths from 5 to 30 μm by difference‐frequency mixing in tellurium. In a demonstration experiment, the SFR laser output is mixed with a fixed‐frequency CO2 laser line to give cw tunable power output near 11 μm. An example of high‐resolution spectroscopy possible with this new source is shown by the spectrum of NH3 which indicates a linewidth of ⩽0.01 cm−1.

Nonequilibrium free hole absorption studies of two-photon magneto-interband transition selection rules in InSb

Abstract The absorption of CO 2 laser radiation by free holes created by two-photon magneto-interband transition has been investigated in InSb. We show for the first time experimentally that, in a transverse magnetic field, the transitions n = ± 1, -3 are explained by the inter-intraband perturbation theory. On the other hand, the tunneling theory must be used to explain the n = 0 transitions.

Study of spin resonance in Hg1−xCdxTe by four-photon mixing

Abstract Four-photon mixing is used to measure spin resonance of conduction electrons in Hg 1− x Cd x Te ( x = 0.23). The magnetic tuning rate and the motionally narrowed linewidth are studied experimentally below and through the quantum limit and comparison is made with theory.

Two‐photon resonance‐enhanced third harmonic generation in deuterium chloride

Two‐photon resonance‐enhanced third harmonic generation of CO2 laser radiation has been studied in DCl. The measurements of the phase‐matched third harmonic signal in a DCl‐CF4 mixture of 1 : 0.010 up to 5 atm show that the third‐order susceptibility for DCl gas is substantially larger than that for the CO gas.

Two‐photon absorption spectroscopy of the intrinsic exciton fine structure in CdS

We have observed the fine structure of two‐photon excited P states in CdS by focusing a dye laser and a CO2 laser into the crystal. From the clear‐cut polarization selection rules, we demonstrate that the visible photon creates a virtual 1S exciton and, subsequently, the infrared photon brings it to the final P state. On this basis, we have calculated the two‐photon absorption coefficient which is in good agreement with experimental data.

Dynamic Stark‐tuned FIR lasers in Rb

Superfluorescent FIR lasers near 50 μm in Rb vapor have been tuned over 800 MHz by using the dynamic Stark effect induced by a Q‐switched CO2 laser beam. The latter is nearly resonant with a transition involving the lower level of the FIR laser. A tuning range of several cm−1 should be possible by using a TEA CO2 laser.

Radiative transitions of photoexcited electrons between Landau levels in n‐InSb

We report the first observation of radiation corresponding to transitions of photoexcited electrons between the two lowest Landau levels in n‐InSb at 2 K. These excited electrons are produced by irradiating a high‐purity n‐InSb sample (n=2×1013 cm−3) with a 10.6‐μm CO2 laser beam. From the study of the radiated power we determine an excited electron density of about 6×1012 cm−3 for an emission frequency of 100 cm−1 and a pump intensity of 2×106 W cm−2.

cw tunable laser‐sideband generation from 5.5 to 6.5 μm by light scattering from spin motion in a spin‐flip Raman laser

We have succeeded in generating cw laser sidebands at wavelengths tunable from ∼5.5 to ∼6.5 μm. The behavior of the power output of the generated radiation is described quantitatively by using the equivalence between four‐photon mixing and Raman scattering from coherent spin motion in a spin‐flip Raman laser.