Interferometric Observation of Absorption Induced Index Change Associated With Thermal Blooming

Abstract

The induced index changes associated with thermal blooming have been observed in iodine-doped CCl4 by means of a Mach-Zehnder interferometer. The interference fringe shape next to the window and the temporal growth of the peak fringe displacement at various positions in the cell have been analyzed. Both the conductive and convective stages of thermal blooming are observed.

Thermal Defocusing of a Co2 Laser Beam in Air Doped With Sf6

“…We have exploited the similarity between the liquid and gas cases by fitting fringe shapes occurring at early times to contours computed from the thermal diffusion equation alone, under the assumption of a Gaussian heating source (2). Figure 7 shows such a lit for a fringe -1 cm from the entrance window at 0.042 sec.…”

Thermal blooming in gases

“…The description of the blooming provided by Equation 1 is valid in liquids until a strong vertical temperature gradient is established. This induces the onset of convective motion in the liquid due to the Rayleigh instability, terminating the conductive phase of the blooming [4].…”

Trace chemical vapor detection by photothermal interferometry

“…2,3 In the late 1960's it was recognized that optical absorption resulting in sample heating and subsequent changes in the index of refraction would induce a phase shift in light probing the heated region. McLean, Sica, and Glass 4 were the first to demonstrate use of an interferometer to measure these photo-induced index changes. Most PTI apparatus are based on laser sources for both excitation and probe.…”

“…The literature indicates that a trace gas sensor with high sensitivity can be constructed using interferometer designs similar to ones previously mentioned. [1][2][3][4]7,8 We have designed, built, and are testing a new instrument for trace gas analysis in ambient air by PTI. The design uses a Jamin interferometer with a specialized optical coating, mid-IR excitation source, and HeNe probe source.…”