Local Thermal Fixing of a Photorefractive LiNbO(3) Hologram by use of a CO(2) Laser.

A real-time, in situ fixing method by use of heating with a CO(2) laser beam is suggested for thermal fixing of a small local hologram in the bulk of a Fe:LiNbO(3) photorefractive crystal. For heating up to 100 degrees C-200 degrees C a volume with a shape similar to that of the laser beam a heat-guiding technique is developed. On the basis of the heat-transfer equations, different heating modes-with or without metal absorbers for heat guiding-obtained by use of a continuous or pulsed laser beam are analyzed. The optimal mode may be pulsed heating with absorbers. On this basis experiments have been designed and demonstrated. It is seen that the fixing process with CO(2) laser beam is short compared with the process by use of an oven, and the fixing efficiency is quite high.