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1 Feb 2001

Volume 89, Issue 3, pp. 1527-1994

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Mechanics of laser-assisted debonding of films

P. R. Tavernier and D. R. Clarke

J. Appl. Phys. 89, 1527 (2001); http://dx.doi.org/10.1063/1.1338519 (10 pages) | Cited 24 times

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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 ΩEp/(dp2math), where Ω is a lumped material constant, Ep is the laser pulse energy, dp is the diameter of the illuminated area and τ 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. © 2001 American Institute of Physics.
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81.05.Dz II-VI semiconductors
81.05.Ea III-V semiconductors
81.90.+c Other topics in materials science (restricted to new topics in section 81)
42.62.Cf Industrial applications

Beat frequencies in a ring laser gyro with its refractive index over unity

Takahiro Numai

J. Appl. Phys. 89, 1537 (2001); http://dx.doi.org/10.1063/1.1337087 (7 pages) | Cited 1 time

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A frequency shift Δf during rotation in a ring laser gyro with its refractive index of unity was already well known. However, when the refractive index nr is over unity, several expressions for a beat frequency such as 2Δf∝nr, nr0, nr−1, and nr−2 were proposed. In this article, a beat frequency in a uniformly rotating ring laser gyro with nr>1 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 nr, as far as the dispersion is neglected. When the dispersion is considered, the beat frequency is in proportion to nr0[1−(rΩ/λ0)2(dnr/df)2]−1, where f is a frequency of a laser beam, λ0 is a wavelength of a laser beam when the ring laser stands still, and nr0 is a refractive index at λ0. If nr0=1−(rΩ/λ0)2(dnr/df)2 is satisfied, the beat frequency seems to be independent of the refractive index. © 2001 American Institute of Physics.
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78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
42.55.Wd Fiber lasers
42.60.Da Resonators, cavities, amplifiers, arrays, and rings
42.81.Pa Sensors, gyros
78.47.-p Spectroscopy of solid state dynamics
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