Adaptive interferometer based on wave mixing in a photorefractive crystal under alternating electric field

Abstract

Coupling of two waves with different polarization states in a photorefractive crystal under an ac electric field allows us to achieve the linear transformation of a small transient phase shift into the intensity modulation without any output polarization filtering. This can lead to design of an adaptive interferometer with sensitivity that reaches the classical homodyne detection limit.

Orthogonal geometry of wave interaction in a photorefractive crystal for linear phase demodulation

“…It is the result of the interference between the non-diffracted vertically polarized component of the object wave and the horizontally polarized component of the input reference wave after its diffraction from the dynamic hologram accompanied by the polarization state rotation. The average phase shift between these polarization components is the sum of three terms: (i) the phase shift between the distribution of the recorded space-charge field and the input interference pattern, which is equal to p/2 in the case of the diffusion recording, (ii) Fresnel's phase shift of p/ 2 that accompanies diffraction from any phase hologram, and (iii) the inherent p/2-phase difference between vertical and horizontal components of the elliptically polarized reference wave [4]. Note that the third term appears in the sum because the horizontally polarized component of the reference beam diffracts from the grating formed by the vertically polarized components of the interacting beams.…”

“…In the diffusion-dominated mechanism (without external field), the quadrature condition are satisfied by employing the vectorial wave mixing technique VWM [4]. In VWM the object and reference waves are mixed in PRC with linear and circular polarization state, respectively.…”

Multi-Channel Adaptive Interferometers Based on Dynamic Hologram Multiplexing

“…Alternatively, holographic recording in the diffusion regime (without external electric field) leads to the less sensitive, quadratic regime of phase demodulation (Kamshilin, et al, 1986). However, as it was shown later by Kamshilin and Grachev, the linear phase-to-intensity transformation can be achieved even in the diffusion regime of the hologram recording if the interfering waves have different polarization states (Kamshilin & Grachev, 2002). The last approach is based on vectorial-wave mixing (VWM) in photorefractive crystals for which the theory was developed by Sturman et al (Sturman, et al, 1999).…”

“…The last approach is based on vectorial-wave mixing (VWM) in photorefractive crystals for which the theory was developed by Sturman et al (Sturman, et al, 1999). It is worth noting that an adaptive interferometer based on the technique proposed in (Kamshilin & Grachev, 2002) operates in so called enhanced diffusion mode when a strong AC-electric field is applied to a crystal for enhancing wave coupling. Further development of VWM-based approach has allowed one to find solutions which it made it possible: -to avoid use of any external electric field due to recording the hologram in pure diffusion mode in reflection geometry of wave coupling at high spatial frequencies (Di Girolamo, et al, 2007a;Romashko, et al, 2005a); -to use an object wave with arbitrary polarization (e.g.…”

A new fiber-optic non-contact compact laser-ultrasound scanner for fast non-destructive testing and evaluation of aircraft composites

“…Other approaches aimed at minimizing the effects of speckle structure include modifications of a Sagnac interferometer [33][34][35][36][37][38] and interferometer schemes employing photorefractive crystals. 31,[39][40][41] However, the detection sensitivity of all these optical techniques does not approach that of a well-designed, contact piezoelectric transducer.…”