| Popis: |
Surface damage thresholds of polished calcite crystals were measured with a pulsed ruby laser at the wavelength of 694.3 nm. Three grades of calcite used for laser polarizers were tested: Grade A, Schlieren-Free, and Scatter-Free, as characterized by the manufacturer, Karl Lambrecht Corporation of Chicago. The test samples were cut and polished with the surfaces parallel to the optic axis. Sample dimensions were 1 cm X 1 cm and 2 to 3 mm thick. The ruby laser oscillator was passively Q-switched to produce 12-ns pulses in a single-transverse and longitudinal mode. Samples were irradiated at near-normal incidence to the 1-cm2 surfaces with a laser 1/e2 spot diameter of approximately 0.12 mm. Tests were conducted with a single shot per site, and photoelectric detection of a laser- induced surface spark was used as a sensitive method for detecting the onset of damage. Damage threshold of 30, 60, and 50 mJ/cm2, were determined for the three grades, respectively. No significant threshold differences were observed between test with the laser polarization parallel and perpendicular to the optic axis. Laser-induced damage, visible by scattering of a collinear He-Ne laser beam, was most frequently observed at the rear surfaces, although it sometimes occurred at the front surface alone or in the interior. On the basis of standing wave electric-field analysis, the predicted energy density at the rear surface was more than twice that at the front surface, and laser damage at the rear surface was expected to occur at a correspondingly lower fluence. Early damage at randomly distributed surface imperfections appeared to preclude such a consistent correlation.© (1997) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only. |
