Holography is the science of generating a 3D image by recording the interference patterns between two light beams; one reference beam and one object incidence beam.
Lasers for Holography and Imaging
Rather than an image as recorded by standard photography, a holographic image is a record of the difference in phase and amplitude intensities of the two light paths as they arrive at the recording media. The resulting interference image is meaningless when viewed under a different light source, but when illuminated by the same light source as used for its creation, the original light path is recreated and the object can be seen as if it were still present. Fine detail, dimensions and the 3D nature of the object can be replicated exactly.
Apart from its frequent application in the arts, holography is also extensively used to prevent forgery in currency or documents, due to the difficulty in reproducing these holograms without the original light source. This requirement for highly accurate phase information is what mandates the use of lasers with excellent spatial and temporal coherence.
Holography is also being hailed as a key technology behind the next wave of Digital Data Storage. It is used to create a 3D interference pattern over the entire volume of the storage material, rather than only on the surface, and greatly increases the information density as well as increasing data read and write speeds.
Holography also underpins the growing applications of augmented and virtual reality devices, which require extremely high resolutions - combining digital holography with tomographic imaging.
Several factors relating to the laser source are critical and common to these Holographic applications.
1. Narrow Linewidth
The coherence length, or narrow linewidth, of the laser is a key characteristic that needs to be considered. Any phase difference between the two light paths will reduce the resolution available in the final image. This is not so critical during the reproduction of holographic plates and the coherence can be much shorter.
2. High Power
As with standard photography, the creation of a holographic image requires an exposure time, which is dependent on the sensitivity of the recording media and the amount of light that is available. Higher power laser outputs offer shorter exposure times and larger fields of view.
3. Wavelength Stability
For static objects in a vibration isolated environment, exposure time becomes less critical and lower power lasers can be considered. Instead, wavelength stability becomes critical, as a slight drift or mode-hopping of the wavelength can cause distortion of the final image.
The final consideration when looking at lasers for holography is the wavelength needed for the best results. Security labels would be ineffective if they were recorded in the IR region, outside the range of the human eye, and many modern holographic images are created using multiple wavelengths - red, green and blue - in order to produce a coloured final image. Holographic applications that do not rely on the eye can be operated out with the visible spectrum and data storage, for instance, would indeed benefit from shorter UV wavelengths, leading to higher information density.
UniKLasers design and manufacture high power, single frequency laser sources with unrivalled wavelength stability, narrow linewidths, and long coherence lengths over a range of wavelengths within a small footprint. We currently offer single frequency lasers in the red and green areas of the visible spectrum with our Solo 640 Series and Duetto 532 Series respectively; to complement our development of a blue Duetto 442, to facilitate high resolution, full colour holograms.