Holography - Holography is a method of recording an objects image in a way that when viewed later, it appears three dimensional. A light field is created by a laser source that illuminates both the object and the recording media. The scattered light from the object interferes with the reference light and it is this interference pattern that creates the image. Light from a laser is split in two and, via optical components, is formed to illuminate the object and the recording media.
Holograms are used in many different areas such as artistic displays, security marking and data storage. This latter application is particularly interesting as it offers the possibility of storing far higher quantities of data compared to magnetic or 2D optical methods, with the added benefit of the data being read at far higher rates.
In order for the interference pattern to be encoded with information about the object, the coherence length of the illuminating light is an important factor, and due to the long exposure times needed, the available power, wavelength stability and divergence of the beam are critical.
The coherence length of the laser becomes less critical when being used to copy/print a hologram and many of our lasers are suitable, however the LSS Series from Laserglow are ideal for all holography applications as the beams have long coherence lengths, divergence and the mode stability.
Holography is an imaging technique in which light scattered from an object is captured on a recording medium. However, unlike a two dimensional photograph, a hologram encodes information for the reproduction of a three dimensional image viewable from different angles.
Holography was discovered by the scientist Dennis Gabor in 1947. In 1971 Gabor won the Nobel Prize in physics for this discovery.
A hologram is produced by illuminating an object with a coherent light source split into an illumination beam and a reference beam, both of which interact at the recording medium. The light source used is a laser which produces coherent light at a stabilized frequency. An optical component called a beam splitter directs half of the light toward the object being imaged (illumination beam) and the other half directly onto the recording medium (reference beam). Mirrors are also used in order to direct the light. The entire setup must be vibrationally isolated and is often mounted on a beam table.
A hologram is produced by the recording of the interference pattern resulting from the interaction of the illumination beam and the reference beam. The illumination beam strikes the object being imaged and upon diffracting off of the object, strikes the recording medium. The reference beam travels from the laser to the recording medium without diffraction. Upon meeting at the recording medium the illumination beam and the reference beam produce an interference pattern unique to the object being imaged. To view the hologram, a source of light matching the reference beam is supplied. The light diffracts off of the pattern in the hologram reproducing an image of the object in three dimensions. When the viewing angle of the system changes different angles of the object can be seen.
A Raman Spectrum features peaks of Raman scattered light, showing their intensity and wavelength position. Each bond or group of bonds within a molecule has a unique molecular vibration and structure. The interaction of light with these vibrating molecular bonds produces unique corresponding peaks on the spectrum. This creates what is essentially a chemical “fingerprint” which can be used to quickly and reliably identify a sample and to characterize its composition. Spectra from Stokes Raman scatter and Anti-Stokes Raman scatter contain the same frequency information. Most Raman spectra are representations of Stokes scatter as most molecules at room temperature exist in the ground state. Anti-Stokes scatter is used for contact thermometry and when Stokes scatter is not easily observable.