Analysis of an active stabilization system for a holographic setup

Abstract

An active stabilization system for a holographic setup based on detection of phase shift between the interference pattern and a reference hologram is described. Its basic feature is the possibility of operating for 0, pi or +/-pi/2 at will, always in a null-detection mode. The reference hologram may be a previously recorded permanent hologram or a real-time (even reversible) one. The use of the open loop response of the stabilization system is developed for analyzing its performance, which allows closer insight into parameters limiting Its behavior. The effects of different noise sources are analyzed in detail. The real-time effect in a positive resist is successfully employed for operating the stabilization setup for recording an improved grating in this material.

Stabilized photorefractive running holograms, with arbitrarily selected phase shift, for material characterization

“…The use of self-stabilization techniques for holographic recording [10,11] in conditions where a nonstationary hologram arises was shown [12] to produce so called fringe-locked running holograms that were later used for analysing the recording process [13] and for material and hole-electron competition [14] characterization in photorefractives [15,16]. The effect of bulk light absorption on the dielectric relaxation and its effect on running hologram recording was demonstrated [17] and taken into account for improving the mathematical model for feedback-operated running hologram recording [18].…”

Voltage Effect in Holograms of Polyvinyl Alcohol with FeCl3

“…Diffraction gratings with high quality can be obtained by increasing the stability of the interference pattern, for reducing noise. Using active control technique, and technique of null detection with piezoelectric mirrors [27,28].…”

Oscillating holograms recorded in photorefractive crystals by a frequency detuned feedback loop

“…[16][17][18][19][20][21][22][23][24][25] Stabilization of a holographic setup using a photorefractive crystal in a two-wave mixing experiment was first proposed by Kamshilin et al 16 The method is based on the active control of the phase shift between the transmitted and diffracted beams that propagate along one of the crystal output directions. Phase is linked to the holographic phase shit between the interference pattern and the refractive index modulation; for a pure index grating and in cases where self-diffraction effects can be neglected, = Ϯ / 2.…”

“…16 is suitable for operating the feedback loop with =0 ͑or ͒. Developments and/or improvements on different aspects of the technique extended its application to = Ϯ / 2, 17 and later to any arbitrary value. 18 By using these techniques, phase-locked photorefractive waves moving at constant velocities have been generated in different applications.…”

“…The technique uses some ideas reported in Refs. [16][17][18] and introduces a quasisynchronous demodulation scheme to create a voltage-controlled phase term into the extracted error signal. This is done through a voltage waveform from a function generator and an electronic time delay circuit, which shift the frequency of the reference wave used for signal demodulation.…”