Choosing Lasers for Holographic Applications

15 October, 2018

News

See our article in Novus Light September 2018:

Choosing Lasers for Holographic Applications

The single most important performance characteristic required when considering lasers for holographic applications is long coherence length, in addition to good power stability, wavelength accuracy and stability, and, above all, excellent reliability.

Developments in laser technology, emulsions and illumination sources have also lead to drastic improvements in the white light holography, which is opening up new applications for holography related to ultra-realistic 3D replication of objects.The performance characteristics of the lasers used to write single or multi-color holograms or HOEs, whether as a master or in volume production, are critical.

White light holography

By far the most important performance requirement on the laser for writing a hologram or HOE is the coherence length. A hologram can more technically be described as a photograph of the light field including its phase content. In order to record the phase content of the light field, the source needs to be coherent. By coherent we mean that all the light waves travel in synchronization i.e., they have the same period and phase, and this characteristic is found in truly single longitudinal mode (SLM) or single frequency (SF) lasers. The coherence length of a light source is directly correlated to the spectral bandwidth of the emitted light (temporal coherence) and the homogeneity of the phase front over the beam cross section (spatial coherence). The distance the light needs to be coherent over in order to make an interference pattern is determined by the depth of field; the larger the depth of field the longer the coherence length that is needed. In general, a coherence length of >1m is more than sufficient.In addition to coherence length, there are a few other parameters which are important to consider. Besides wavelength, they are: output power, wavelength accuracy and stability, as well as reliability.

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