Absorption coefficients of weakly absorbing solids: theory of a barothermal gas cell.

For the case in which a laser beam passes through the weakly absorbing windows of a cell containing a non-absorbing gas, the temperature profiles in the cell windows and the pressure and temperature profiles in the gas have been calculated. Both the transient response and steady-state behavior of the cell are examined when the barothermal conditions are valid. These calculations suggest that sufficient heat transfers by thermal conduction from the weakly absorbing windows into the gas to produce a measurable pressure rise in the gas. The theory contains the two assumptions that bulk absorption in the window is the mechanism by which energy is transferred from the laser beam to the windows and that the window and adjacent gas are in good thermal contact. Numerical examples for a laser glass and air (nitrogen) are given.