Resonant nonlinear 10 μm refraction of ammonia at low pressure measured with new HgCdTe detectors

• Published in: Infrared physics & technology 1998-10, Vol.39 (6), p.369-391
• Main Authors: Baumgartner, M.O., Kneubühl, F.K.
• Format: Article
• Language: English
• Subjects: Ammonia; Beam trapping, self-focusing and defocusing; self-phase modulation; Beam trapping, self-focusing, and thermal blooming; Bolometer; infrared, submillimeter wave, microwave and radiowave receivers and detectors; Bolometers; infrared, submillimeter wave, microwave, and radiowave receivers and detectors; CO 2-laser; Exact sciences and technology; Fundamental areas of phenomenology (including applications); HgCdTE detectors; Infrared, submillimeter wave, microwave and radiowave instruments, equipment and techniques; Instruments, apparatus, components and techniques common to several branches of physics and astronomy; Nonlinear optics; Optics; Physics
• ISSN: 1350-4495; 1879-0275
• DOI: 10.1016/S1350-4495(98)00028-0

In this paper we report on nonlinear interactions of 10 μm CO 2-laser radiation with ammonia molecules. In order to study these effects, the CO 2-laser radiation was tuned to resonance with the ν 2-vibration of NH 3 in a first step. This caused a high nonlinear polarization of the NH 3 gas. Then we determined the resulting self-focusing of the laser radiation as a function of the NH 3 pressure. In addition, we have studied the phase modulation induced by the nonlinear refractive index ( n 2) with the aid of a Mach–Zehnder interferometer. Since the modulation of the phase is proportional to the inducing laser intensity, we have succeeded in determining the molecular nonlinear refractive index γ for the wavelengths 10.334 μm, 10.349 μm and 10.365 μm. The experiments described demanded the use of highly sensitive fast 10 μm HgCdTe detectors. Therefore, we have determined the linear response of four of these detectors as well as their response time with the aid of an optical free induction decay (OFID) 10 μm-CO 2 laser system which yields 35 ps 10 μm pulses. The measured rise times τ 10–90% of 1.4 ns to 3.3 ns equal the fall times.