Henning Rehn

BEAM-FANNING NOVELTY FILTER WITH ENHANCED DYNAMIC PHASE RESOLUTION

We demonstrate a novel method to enhance the phase resolution of a barium titanate beam-fanning novelty filter by means of an external phase shift in one part of the signal wave. The new technique is described theoretically on the basis of the coupled-wave theory. Experimental results are presented to demonstrate the behavior and the advantages of the novel device for the evaluation of spatial and temporal phase changes in incident signal waves.

Experimental investigations of the external self-pumped phase conjugate mirror

Abstract Reported are experimental investigations of a barium titanate self-pumped phase conjugate mirror (SPPCM), where the pump waves are generated by means of a concave mirror. The principle of this type of SPPCM has been described theoretically but has not been investigated carefully under various experimental conditions. The use of this SPPCM instead of the usual “cat” SPPCM results in several advantages such as a considerable shorter response time.

Photorefractive two-wave mixing and the lambert W function

A stationary solution for photorefractive two-wave mixing with arbitrary modulation is expressed in closed form in terms of the Lambert W function.

Transient phase measurement using a self-pumped phase-conjugate mirror as an optical-novelty filter

A transient phase-measuring technique that uses a self-pumped phase-conjugate mirror as an optical novelty filter is presented. A change in the reflectivity of the mirror as a function of a change in the incident wave front permits the transient measurement of a two-dimensional phase distribution. This method allows us to investigate fast processes using media with slow response. A simple theoretical model explains the experimental results with sufficient accuracy. The results can be used for the calibration of the measuring system. The described method is used for the measurement of a temporally varying wave front.

Azo-dye-doped polymers as novel optical storage media in holographic interferometry

We describe a real-time holographic interferometric set-up for the determination of dynamic deformations of reflecting surfaces. The optical storage medium used is based on the novel polymer poly(vinyl alcohol) with alkoxyazobenzencarbonyl substituent. This material does not need any development and is characterized by low costs.

Photorefractive novelty filters for transient phase evaluation

In our report we compare different ways of realizing an optical novelty filter with photorefractive barium titanate crystals. We present experiments on the basis of beam fanning, two-wave mixing and self-pumped phase conjugate geometries. The application of photorefractive novelty filters not only for phase visualization but also for the measurement of transient phase changes in a laser beam is demonstrated. The phase calculation from an interferogram is supplied or replaced by the novelty filters phase transfer function. The use of such techniques instead of conventional interferometry for transient phase evaluation results in a simplified measuring procedure.

New image processing technique for transient fringe evaluation

Our technique allows for the evaluation of a cross-section of a fringe pattern with a temporal resolution of 40 ms over a range of 20s. It can be applied to all two-beam interferometer, fringe projection, or ESPI techniques if a phase shift device is a part of the optical set-up.

Stationary and transient interferometry with a self-pumped phase conjugate mirror

For the application of self-pumped phase-conjugate mirrors in interferometric arrangements, the properties of such devices have to be characterized. In this paper, we define figures of merit on the basis of experimental investigations and show, how the field of possible interferometric applications is limited in the case of a non-ideal phase conjugation process under stationary and transient conditions.

Measurement of phase differences with a novelty-filter phase-step technique

We present a technique for the measurement of temporal phase differences. In this method, the holographic storage of a given wavefront in a photorefractive BaTiO3 crystal is combined with the interferometric phase-step technique. We obtain a novelty-filter phase-step method which allows for the measurement of phase changes within a unique process. The application and some features of the technique are demonstrated.

Incoherent-to-coherent conversion via photorefractive fan-out and two-wave mixing

Abstract We report a novel scheme for an incoherent-to-coherent converter by means of the selective erasure of the random dynamic gratings created by the beam-fanning process in BaTiO3. Furthermore, the spatial resolution properties of a two-wave mixing incoherent-to-coherent converter are discussed in the geometrical limit, and using the two-dimensional two-wave mixing theory.