Thermal effects in laser-assisted pre-embryo zona drilling

Diode lasers [lambda = 1480 nm] are used with in vitro fertilization to dis sect the zona pellucida (shell) of pre-embryos. A focused laser beam is app lied in vitro to form a channel or trench in the zona pellucida. The proced ure is used to facilitate biopsy or as a promoter of embryo hatching. We pr esent examples and measurements of zona pellucida ablation using animal mod els. In using the laser it is vital not to damage pre-embryo cells, e.g., b y overheating. In order to define safe regimes we have derived some thermal side effects of zona pellucida removal. The temperature profile in the bea m and vicinity is predicted as function of laser pulse duration and power. In a crossed-beam experiment a HeNe laser probe is used to detect the tempe rature-induced change in the refractive index of an aqueous solution, and e stimate local thermal gradient. We find that the diode laser beam produces superheated water approaching 200 degreesC on the beam axis. Thermal histor ies during and following the laser pulse are given for regions in the neigh borhood of the beam. We conclude that an optimum regime exists with pulse d uration less than or equal to5 ms and laser power similar to 100 mW. (C) 20 01 society of Photo-Optical Instrumentation Engineers.