Holographic optical element

HOEs may be regarded as a generalization of Fresnel lenses and their definitions partly overlap—for instance, the kinoform structure shown in Fig. 2.2e is a typical HOE. We may say that Fresnel lenses are a subgroup of holographic optical elements. 

In Fresnel-type HOEs, the light distribution in the hologram plane is the Fresnel diffractive image of the object. For radially symmetrical kinoforms (rings and circles), 2D Fourier and Fresnel integrals are reduced to ID Hankel s integrals [146]. 

DOE lenses for HgCdTe detector arrays were described within the context of HgCdTe detector focal plane arrays [150]. Diffractive (8-16-phase-level) Ge microlenses reducing the detector size in focal plane arrays by 3-6 times were described in [151]. 

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Holographic optical elements can also be made by the preparation of polymer-dispersed liquid crystals using twin lasers in transmission holographic photopolymerisation (see section 5.4.2). They have also been made using photorefractive composites of polymer dispersed liquid crystals (see section 5.6.3). 

Holographic Optical Elements in Liquid Crystal Display Systems... 

The technology associated with holographic optical elements (HOEs) existed for some time before applications to spectroscopy but were applied to Raman... 

Gel permeation chromatography Planck constant Hydroxyethylmethacrylate Holographic optical element Intensity... 

Luna D., Olivares A. Barriel L. (1977). Photoresist shipley 1350- with crystal violet tint for holographic optical elements. Optical Materials, 7,189-195. 

The interest to static volume holograms with thickness of several millimeters is due, mainly, to their use in research and in creation of holographic optical elements (HOE) of various purposes with unique parameters (Sukhanov et al., 1984 Ludman at al., 1997 Popov, et al., 2000 Luo, at al., 2008). Requirements to materials for recording of such holograms are rather specific and cannot be met when using traditional light-sensitive materials. 

It has been proposed that holographic optical elements (HOEs) could achieve concentrations in the range 10-20 x without tracking by stacking individual elements designed to be effective at different times of the day. This is impossible, as indicated by the dashed box in Fig. 15, because it would violate the thermodynamic limit. 

H Owen, D Battey, MJ Pelletier, JB Slater. New spectroscopic instruments based on volume holographic optical elements. Bellingham, WA SPIE, 1995, pp 260-267. 

From the point of view of coupling efficiency (minimization of reflection losses), the best solution is monolithic or hybrid integration however, in practical situations one can encounter all of the mentioned approaches. Two main types of focusing lenses may be used—either refractive lenses fabricated in material with high real part of refractive index and low absorption coefficient at IR wavelengths, or diffractive lenses. Any of them may be either discrete or arrayed. Reflective optical concentrators may be used, also reflective holographic optical elements or any of their combinations. 

If a DOE is fabricated using holography, it is called a holographic optical element (HOE). The terms HOE and DOE are sometimes used interchangeably. 

H. Owen, Volume phase holographic optical elements, in Handbook of Vibrational Spectroscopy, J. C. Chalmers and P. R. Griffiths, Eds., Wiley, Chichester, West Sussex, England, 2002, Vol. 1, p. 482. 

Volume holographic optical elements developed for military uses, are successfully applied for Raman spectroscopy a so-called notch filter reflects a laser line virtually completely, its intensity is reduced by >6 orders of magnitude, with a transmission of about 70% at the other wavelengths. 

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