Dynamics of a mode-locked low-pressure photolytic I* laser

A longitudinally pumped photolytic iodine laser has been reliably mode-locked over a broad range of iodide pressures (1-30 Torr). Average mode-locked pulse widths ranging from 1.4-2.5 ns were observed as a function of CF₃I iodide pressure and added buffer gas (Ar). Low-pressure data indicate an increased gain bandwidth as a result of an initial nonthermal I* atom distribution following rapid (<20 ns) photolysis of the parent molecule, CF₃I. Nearly 1.75 eV of excess pump energy is available and is deposited into the internal vibrational and rotational degrees of freedom of the large radical and into the translation of the nascent iodine atom, allowing for high iodine atom velocities in the frame of observation. A diode laser system tuned to the 3-4 transition of spin-orbit excited iodine atoms was used to observe the time-dependent behavior of line center gain along the optical axis. Preliminary data indicate an I* atom velocity relaxation on the order of 1 μs for an iodide pressure of 1 Torr, and approximately 300 ns for a pressure of 10 Torr. At 5 Torr of CF₃ I, the laser mode build up time is 200 ns, allowing access to the increased gain bandwidth and resulting in mode-locked pulse widths less than the predicted transform-limited pulse width for an inhomogeneous gas laser