Volume 89, Issue 3, 01 February 2001
Index of content:
- LASERS, OPTICS, AND OPTOELECTRONICS (PACS 42)
89(2001); http://dx.doi.org/10.1063/1.1338519View Description Hide Description
Films of GaN and ZnO can be separated from the substrates on which they are grown by the use of a laser-assisted debonding process in which a pulsed laser is shone through the substrate and absorbed in the film. Experience shows that the success in separating the films intact and damage free depends sensitively on the laser parameters used and the physical and geometric properties of the films. In this contribution, the mechanics of the laser-assisted debonding of GaN films are presented and used to construct process maps that delineate the conditions for damage-free film separation. The key variable is the nondimensional group where is a lumped material constant, is the laser pulse energy, is the diameter of the illuminated area and is the laser pulse length. Experimental observations of UV/excimer laser assisted debonding of GaN films from sapphire substrates are used to illustrate the types of deformations and cracking modes on which the process maps are based.
89(2001); http://dx.doi.org/10.1063/1.1337087View Description Hide Description
A frequency shift during rotation in a ring laser gyro with its refractive index of unity was already well known. However, when the refractive index is over unity, several expressions for a beat frequency such as and were proposed. In this article, a beat frequency in a uniformly rotating ring laser gyro with is calculated using nonrelativistic, special relativistic, and general relativistic theories. To the first order, all the results obtained from these theories show a common beat frequency, which is proportional to the refractive index as far as the dispersion is neglected. When the dispersion is considered, the beat frequency is in proportion to where f is a frequency of a laser beam, is a wavelength of a laser beam when the ring laser stands still, and is a refractive index at If is satisfied, the beat frequency seems to be independent of the refractive index.