A multilens high pressure H2 cell has been used to demonstrate that efficient, high optical quality and low threshold down-conversion to 1st Stokes can be obtained also with a poor quality broadband pump, with just the condition that the pump pulsewidth is larger than the cell transit time. A backward 1st Stokes with 0.7 overall quantum efficiency conversion has been obtained from a broadband Nd:YAG duplicated laser.

By using the spectroscopic constants recently reported, it has been possible to assign many FIR transitions in dimethyl ether (CH3OCH3) and methyl fluoroform (CH3CF3) that have been previously published in the scientific literature. Several of these assigned transitions have high quantum numbers and they can be used to improve the accuracy of the spectroscopic constants.

The refractivity around an absorption band is related to the strength of the band absorption. In this work this relation is used to derive the CO2 vibrational band strengths from the accurate measurements of the refractivity and to accurately represent with a simple expression the refractivity behaviour of CO2 from the visible to the microwave region.

The refractive index of SF6 has been measured at low pressure with some CO2 laser lines in the 9–11μm region. These measurements can be related in a simple way to the ν3 absorption band by means of a simple quantum mechanics relation that allows to calculate the refractive index behaviour over a frequency range much larger than the bandwidth, and to derive the integrated band absorption intensity. With this method the absolute intensity Sν0=19.03(16)×10-17cmmolecule−1 has been measured for n-SF6 ν3 band.

By means of an interferometric technique we have determined the refractive index of ammonia for the 9P18–9P26 CO2 lines. A calculation model is also reported to derive from these refractive index measurements the dispersion contribution of the sR(3,K) multiplet, resonant with the 9P20 line. This dispersion is the main responsible of the phase mismatching of the resonant four waves MIR generation observed under the strong resonant Raman scattering of this CO2 line in ammonia. The calculated corresponding time modulation is in good agreement with the observed modulation of the experimental MIR pulses.

The refractive index of carbon-dioxide, nitrogen, helium, oxygen and air have been measured at 23°C temperature by means of a tunable CO2 laser at 10.57μm and of a differential interferometric technique. As the gas refractive index depends on the pressure P as n=1+αPP, the pressure coefficients αP has been measured with 5e–3 accuracy.

The CO2 refractivity has been measured at several CO2 laser lines with a better accuracy than in previous works. The observed dependence on frequency shows the effect of the CO2 absorption bands at 15μm and 4.3μm even if they are well far from the frequency region under analysis.

The dynamics of the Resonant Raman Scattering (RRS) of multimode broadband lasers is described and resolved without neglecting the phase and cavity effects. The multimode pump structure leads to an equivalent Raman structure by mixing interaction. When the stokes and the pump modes have the same phase, the forward multimodal Raman scattering shows a gain equivalent to the gain of a single mode pump with an equivalent mean power, so that in a Raman resonator the Raman modes can be synchronously amplified to the saturated power until the de phasing destroys the Raman conversion. All these effects have been experimentally observed. Besides an incoherent scattering process is always present in competition with the coherent one.

The refractive index of some simple molecules has been determined with different CO, laser lines in the 10 mu m region. Some gases show a frequency dependence of the refractive index. This frequency behaviour can be related in a simple way to the presence of an absorption band adjacent to the 10 mu m region. This simple relation allows to derive with good accuracy the integrated absorption intensity S,. of the involved bands. In this way the model validity is confirmed and the model can be used to calculate the theoretical refractivity over the whole IR region (< 5000 cm(-1)) by using the S-x(0) values of all the IR bands reported in literature. (c) 2005 Elsevier B.V. All rights reserved.

The “anomalous” dispersion of the refractive index has been determined around the 10P18 CO2 absorbing line by recording the spectrum of a mode tunable CO2 laser emission transmitted through a high quality Fabry–Perot resonator. The weak phase shift observed agrees well with the usual quantum mechanic treatment of a two level transition.

The analysis of the FIR emission of Ammonia inside a laser cavity shows the transition from a superfluorescent pulse starting from a lethargic gain to the behaviour of the cavity stimulated emission.

The assignment of the NH MIR rotational laser lines previously observed (T. Tillert, et at. Int. J. of IR&MMW 17,1011-21(1996)) inside the 2ν vibrational level is reported. The most part of the reported emissions of this isotopic species is due to the off resonance two photon pumping (Oa->1s->2a) with intermediate detunings as large as 800GHz

The assignment of the 15NH3 MIR rotational laser lines previously observed (T. Tillert, et at. Int. J. of IR&MMW 17,1011-21(1996)) inside the 2ν2 vibrational level is reported. The most part of the reported emissions of this isotopic species is due to the off resonance two photon pumping (Oa->1s->2a) with intermediate detunings as large as 800GHz

In this work is reported the assignment of the NH3 MIR rotational laser lines previously observed inside the 2ν2 vibrational level. Some of them are due to the one photon pump of the hot band 1s->2a, the most part is assigned to off resonance two photon pumping (0a->1s->2a) induced at intermediate detunings as large as 600GHz

The assignment of the 15 NH 3 MIR rotational laser lines previously observed (T. Tillert, et at. Int. J. of IR&MMW 17,1011-21(1996)) inside the 2ν 2 vibrational level is reported. The most part of the reported emissions of this isotopic species is due to the off resonance two photon pumping (Oa->1s->2a) with intermediate detunings as large as 800GHz

The usual laser rate equations have been applied to fit energy and shape of pulsed emissions of RF CO 2 single mode lasers starting from the discharge and cavity parameters. The model well reproduce the laser behaviour, if to fit the turn-off normally observed in these lasers we introduce a phase laser gain correction related to the frequency chirp.

The dynamics of multiple Raman scattering in a long, path liquid nitrogen (LN2) cell is analysed by using a long, pulse unfocused Nd-YAG laser. This medium in this configuration is the most suitable to evaluate the window and mixing effects in the dynamics of the Raman process. In this experiment the window reflections have been evidenced in the time behaviour and they have a calculable effect to lower the Raman threshold. Moreover, some four wave mixing effects have also been calculated and observed both reducing the threshold for the second Stokes scattering and producing a pump regeneration.

A model is reported to foresee ,for different mirror choices, the spectral properties of a high pressure, frequency tunable, CO 2 laser, operating with a non-Littrow grating mounting. The calculations show a larger frequency selectivity for not collimated plane cavities. The model is experimentally verified in a suitable high pressure laser. In particular narrowed linewidths less than 300MHz ( FWHM) are obtained.

A dynamical model giving the infrared plasma reflection in a semiconductor is used to reproduce the transient reflectivity at 10.6 µm due to an intense photo-plasma. In this way we have derived the `cubed' coefficient of the Auger recombination in indium arsenide and gallium antimonide from the stationary peak reflectivity produced by a ns Nd laser. We have derived the cubic coefficients 12(4)×10-27 cm6 s-1 and 9(3)×10-28 cm6 s-1 for InAs and GaSb respectively.

In order to reproduce the transient IR-FIR reflectivity and transmission due to an intense photo-plasma generated by a fast laser pulse at a frequency above the band gap, we have used a dynamical model of plasma evolution. In this way we have derived both the `quadratic' and `cubed' coefficients of the Auger recombination in indium antimonide, by analysing the transient reflectivity at 10.6 µ and 119 µ induced by a fast Nd pulse. In particular we have derived a cubic coefficient of about 7±3×10-26 cm6 s-1, a result larger than those derived in previous experimental works but quite in agreement with the theory.