Infrared Multiphoton Absorption by Methanol

Abstract

The multiphoton absorption of CO2 laser 9 μm P(18), P(20) and P(34) lines by methanol has been studied for fluences from 10−3 to ∼ 20 J/cm2, pulse widths of 6 and 60 ns FWHM and methanol pressures from 0.067 to 13.3 kPa. The absorption depends on laser fluence, laser line and gas pressure but not on laser beam intensity. For each line studied the results can be expressed as a function of fluence and the product of pressure with pulse width. Absorption by a Q‐branch transition (9P(34) pumping) shows a faster relaxation and a stronger absorption than R‐branch transitions (9P(18) and 9P(20) pumping). The results obtained here are compared to multiphoton absorption data for an HF laser pumping the OH stretch vibration.

Multiphoton absorption and decomposition studies of chloroform-d induced by a pulsed 13CO2 laser

“…3. These results show a behaviour similar to the PAT (where AT is laser pulse width) dependence observed for constant @ for CDF, (3 l), CH30H (32), and cyclobutanone (33) and fits the empirical equation [2] [ l ] are negative), absorption of the laser light during transmission through the CDC13 significantly reduces + in the region of the gas that the microphone samples. This, as has been discussed in ref.…”

“…This, as has been discussed in ref. 32, leads to a large uncertainty in the results, and consequently we do not report u values for the photoacoustic measurements. However, from the MPA results, (n)(+) for + = 10 J/cm2 has been estimated using several laser lines.…”