System for acquiring images by means of heterodyne digital holography

#The present application relates to the field of image acquisition, and more particularly aims at a system for acquiring images by heterodyne digital holography.

#Digital holography generally designates techniques enabling to record, by means of a digital image sensor, the phase and the amplitude of a coherent light beam after reflection or transmission by an object.

#Usual holography techniques are based on the use of the interference generated by the superposing of two coherent light beams, where the first one, or object beam, is transmitted or reflected by the object to be examined, and the second one, or reference beam, does not cross the object to be examined.

#The foregoing and other features and advantages will be discussed in detail in the following non-limiting description of specific embodiments in connection with the accompanying drawings, among which:

#FIG. 1 schematically shows an example of a system for acquiring images by heterodyne digital holography;

#FIG. 2 is a diagram illustrating an example of operation of the system of FIG. 1;

#For clarity, the same elements have been designated with the same reference numerals in the various drawings and, further, the various drawings are not to scale. Further, only those elements which are useful to the understanding of the described embodiments have been detailed. In particular, the various uses which may be made of a system for acquiring images by heterodyne digital holography have not been detailed, the described embodiments being compatible with all known applications of heterodyne digital holography.

#FIG. 1 schematically shows an example of a system 100 for acquiring images by heterodyne digital holography.

#System 100 comprises a light source 101 (L) capable of generating a coherent light beam of frequency fL, for example, a laser source. System 100 further comprises a splitter 103, for example, a partly transparent and partly reflective blade 103 placed with a 45-degree angle relative to the emission direction of source 101, enabling to divide into two portions the beam generated by source 101. At the output of splitter 103, a first beam portion, or reference beam R, is modulated by a first acousto-optic modulator MAO1 shifting its frequency by a value fMAO1, and a second beam portion, or object beam O, is modulated by a second acousto-optic modulator MAO2 shifting its frequency by a value fMAO2 different from value fMAO1. The system is arranged so that the object beam, of frequency fL+fMAO2, illuminates an object 105 (OBJ) to be examined, while the reference beam, of frequency fL+fMAO1, does not cross object 105. The reference beam and the object beam reflected or transmitted by object 105 are then directed towards a recombination element 107, for example, a beam splitter, which recombines them. The resulting beam provided by element 107, comprising both the object signal and the reference signal, is projected on an image sensor 109 comprising a pixel array (not shown in FIG. 1).