Generation of acoustically distributed feedback lasers based on gyrotropic crystals

Abstract

Oscillation conditions were determined for acoustically distributed feedback (ADFB) lasers based on gyrotropic uniaxial and cubic crystals. The lasing threshold was shown to be higher for the modes with clockwise polarization than for those with counterclockwise polarization. It is established that the regions of maximal amplification for clockwise (counterwise) waves of the gyrotropic crystal are displaced in the direction of decreased (increased) phase detuning, respectively, relative to amplification regions that correspond to the absence of crystal gyrotropy. The ADFB laser was shown to be capable of generating at the Bragg frequency.Introduction. Acousto-optical crystals (Bi 12 SiO 20 , Bi 12 GeO 20 , Bi 12 TiO 20 , TeO 2 , Te, α-HIO 3 ) possess gyrotropic properties [1,2]. Continuous laser generation was produced in Bi 12 SiO 20 :Nd 3+ crystals with an end resonator using radiation from a tuned Ti 3+ :Al 2 O 3 laser with λ pump = 0.814 µm for crystallographic direction [100]. Feedback in this laser was effected by highly reflective mirrors. The threshold pumping power for generation at λ em = 1.0716 µm was ~18 mV.Lasers with distributed feedback (DFB) and acoustically distributed feedback (ADFB) are used widely in various areas of science and technology [4][5][6]. Reflective phase lattices in photorefractive crystals are the principal element of DFB lasers and form coherent light waves at large convergence angles of interfering beams [2,7]. Light-diffraction features in static phase lattices in gyrotropic cubic crystals using inverse Bragg reflection have been investigated [7,8]. Two regimes of Bragg diffraction with inverse reflection in gyrotropic media have been defined [8]. These have a monotonic increase of the diffraction effectiveness with increasing coupling constant for ρ 2 ≤ χ 2 (ρ is the specific rotation parameter; χ, the coupling constant of interacting waves) and with an oscillatory change for ρ 2 > χ 2 . The coupling of oppositely directed modes in ADFB lasers is effected by an acoustic wave that propagates along the resonator axis [6]. Energetic and phase conditions for laser generation with DFB based on gyrotropic cubic crystals have been published [9]. It should be noted that whereas gyrotropy in uniaxial and biaxial crystals appears only for light-propagation directions close to the optical axes, it must be considered for any light-propagation directions in cubic crystals [10].Herein features of ADFB lasers based on gyrotropic uniaxial and cubic crystals are investigated. Light and ultrasonic waves are propagated along optical axes of uniaxial crystals or crystallographic directions of cubic crystals.Calculations. Let us assume that an ultrasonic phase lattice is located in an amplifying medium between planes z = 0 and z = l. The incident light wave is linearly polarized and can be represented as a sum of clockwise and counterclockwise polarized waves, i.e., A = A 01 e + + A 02 e -, where A 01 and A 02 are amplitudes of the circularly polarized components and e ± = (e 1 ± ie 2 ) ⁄ √ ⎯ ⎯2 ...