M. Blanchard

Performance characteristics of a TEA double-discharge grid amplifier

A novel discharge circuit for the pulsed excitation of a double-discharge grid-cathode TEA-CO 2 amplifier is described. A distinctive feature of this circuit is the use of an underdamped preionizing discharge, together with a slow rate of electrical energy injection in the amplifying medium. Significant improvements in the stability and uniformity of the discharge is obtained by increasing the pumping period to the 2-6 \mu s range. Small-signal gain coefficients up to 0.035 cm-1are achieved in a 5 \times 5 \times 50 cm3discharge volume with an electrical input energy density as low as 120 J/l. Details concerning the design and operation of the circuit are given. The temporal dependence of the gain upon circuit parameters, gas mixture composition, and electrical energy input is studied, and an investigation is made of the spatial gain distribution and optical homogeneity over the amplifier cross section. Measurements of the gain-saturation characteristics with a 2-μs probing pulse indicate a value of 5.8 \times 10^{-20} cm2for the stimulated emission cross section.

Plastic recording media for holography at 10.6 μm

A search for recording media suitable for holography at wavelengths comparable to the 10.6 microm of a CO(2) laser has led to the successful use of Saran Wrap plastic films and of thick acrylic plates. Holographic phase recording has been made with a 1-W single mode cw CO(2) laser yielding incident intensities up to 3.5 W/cm(2). Holographic reconstruction at a wavelength of 632.8 nm has given a diffraction efficiency up to 20%. At a wavelength of 10.6 microm, reconstruction by reflection on the silver-coated surface of an acrylic plate had a diffraction efficiency of 0.5%. It was observed that the recording is less linear on acrylic plates than on Saran Wrap films.

Pulsed ir holography on Takiwax films

Phase holograms have been recorded on Takiwax films with pulsed TEA CO(2) laser light. The reconstruction from these phase holograms is accomplished by transmission at a wavelength of 0.633 microm. Holographic characteristics of the recording medium, such as diffraction efficiency vs film thickness, exposure, and spatial frequency, are presented. The capability of Takiwax films to record ir holograms of plane objects and double-exposure holographic interferograms is demonstrated.

Holographie en infrarouge sur de minces couches d'huile.

Oil films of approximately 1-microm thickness on glass plates are used as a holographic recording medium at a 10.6-microm wavelength. This dynamic recording medium (on which the recording is not permanent) shows diffraction efficiencies up to 20% when reconstructing at 632.8 nm, the spatial frequency at the recording being as high as ~50 cycles/mm. Furthermore, the response time of these oil films when recording ir can be as small as 2 msec so that ir holography of moving objects is possible in real time.

Fluorescence A 4.3 μm en fonction de la pression dans un laser CO2 supraatmospherique

Abstract We have observed the 4.3 μm fluorescence signal produced by a superatmospheric double-discharge CO 2 laser, up to a pressure of 5 atm. The evolution of the signal amplitude with pressure reveals an unusual behaviour which we associate to the hot bands. Moreover, we have deduced the V-V relaxation times of CO 2 in mixtures CO 2 :N 2 :He of (10:5:85) and CO 2 :He of (9:91).