J. Ducuing

Vibrational relaxation of ortho and para-H2 in the range 400-50 K

Abstract The vibrational relaxation of ortho-para-H 2 mixtures was studied in the interval 400-50 K. At and above 300 K the ortho and para self-relaxation rates, k oo and k pp , are identical within experimental error. In the low temperature range, k oo > k pp and k oo is found to vary slowly with temperature.

Experimental study of the vibrational relaxation of ortho and para-H2 in collisions with 4He in the range 300–50 K

Abstract The vibrational relaxation of ortho-para-H 2 in collisions with 4 He has been studied in the interval 300–50 K. At 300 K the ortho H 2 - He and para H 2 - He rates are identical within experimental error. In the low temperature range .

Tunable, millijoule radiation extending to the 16 μm region

Abstract Efficient Stimulated Raman Scattering (SRS) in liquid nitrogen between 15 and 18 μm was obtained. Infrared radiation output was continuously tunable and narrow-band with energies up to 1.7 mJ.

Powerful tunable infrared and far-infrared Raman sources

Abstract The generation of powerful and monochromatic tunable radiation in the infrared and far-infrared spectrum has been obtained by successive frequency shifts of a tunable source by stimulated Raman scattering. According to the spectral region of interest, different Raman media have been used: gaseous hydrogen, liquid nitrogen and gaseous hydrogen halides. In the latter case, the use of hydrogen fluoride permits a coverage of about 40% of the 40–240 cm −1 range. In each step of the frequency shift the quantum efficiency is between 50 and 10%. Even at the largest wavelength (250 μm) the number of photons created was larger than 10 17 per pulse (2.5 nsec duration).

Two-photon absorption in organic dyes — reply to a comment

Abstract In a recent issue of this journal, Scha¨fer and Schmidt criticized the experimental method and the results of several of our papers. We show that this criticism is unjustified and that there is no more experimental support than theoretical grounds for their geometrical model of two photon absorption.

Tunable Infrared Generation in Molecular Gases

In recent years the use of nonlinear optical processes in gases to generate tunable infrared radiation has received renewed interest. Although gases, in opposition to solids, show no second order dipolar nonlinearity their third order susceptibility can be considerably enhanced through resonances and lead to strong interactions. Furthermore gases offer many advantages over solids: higher damage threshold, broader transmission range, better optical quality and larger volume. Until now, most of the work on tunable generation has concentrated on metal vapours [1–3], which near resonance exhibit very large susceptibilities. However room temperature molecular gases which are considerably simpler to deal with, can also support strong interactions, as evidenced long ago by the easy appearance of stimulated Raman scattering in H2, CH4 and a number of other gases [4], H2 is of special interest, as it shows no electric dipole absorption in the whole infrared spectrum. In the following we discuss the generation of tunable medium infrared through 4-wave interactions in this gas and present results obtained in the range 5–16.5 μm. We also consider a scheme for the efficient generation of tunable far infrared through resonantly enhanced stimulated Raman scattering in HF.

Tunable far-infrared Raman generation

Abstract Resonance enhanced stimulated Raman scattering of a tunable laser was observed in the 60–160 μm range for the Q(J) transitions in hydrogen chloride. The resultant far-infrared source was tunable over about 2.3 cm −1 around each transition studied (J = 2 to 7) and gave a peak power around 80 kW corresponding to a photon efficiency of the order of 12%.