Dispersive resonators with volume holographic gratings

A dispersive resonator with volume holographic phase gratings for a tunable laser is described. The experimental results showed advantages of these resonators over the analogous devices using blaze-angle reflection relief gratings.     

Developed profile of holographically exposed photoresist gratings

A simulation of the profile of holographically recorded structures in photoresists is performed. In addition to its simplicity this simulation can be used to take into account the effects that arise from exposure, photosensitization, development, and resolution of positive photoresists. We analyzed the effects of isotropy of wet development, nonlinearity of the photoresist response curve, background light, and standing waves produced by reflection at the film-substrate interface by using this simulation, and the results agree with the experimentally recorded profiles.     

Interferometric fabrication of modulated submicrometer gratings in photoresist

Interferometric recording is applied to the fabrication of modulated submicrometer gratings in photoresist.High diffraction efficiency requires optimized recording conditions, which are obtained by the use of an on-axis continuous surface-relief grating for the generation of the object beam. The optimized phase function is copied into the resist layer by means of a self-aligned two-step recording process with an intermediate copy in a volume photopolymer hologram. As a result, we demonstrate high carrier frequency surface-relief off-axis fan-out gratings for illumination in transmission with visible light.     

Development in situ for gratings recorded in photoresist

A technique for developing recording gratings in situ in Photoresist Shipley S-1822 is described. The developing process is accomplished by use of a spray without removing the sample from the optical setup. The results for the diffraction efficiency show that there is not a large difference between gratings achieved with the traditional wet development process and those obtained with the in situ developing technique. The potential of this in situ developing technique is shown with a moiré interferometric experimental setup used for displacement showing.     

Applications of holographic gratings to two-dimensional spectroscopy

Calculations are presented for a set of aberration-corrected holographic concave gratings for possible use in space mission instruments. It is concluded that, for the visible range 0.26-1.02 μm when detectors with a 15-μm pixel size are used, a total field of view of ～1° is possible at an aperture of ?/7.0. For the infrared regions 0.9-2.5 μm and 2.4-4.2 μm, in which detector arrays have larger pixel sizes of 30-40 μm, a spatial field of view of ～2° at ?/7.0 and ～1.0° at ?/3.5 can be achieved. An exploration of spectrum lengths showed that performance starts to fall off sharply for lengths over 15 mm at a focal length of 150 mm (i.e., a spectral angular extent of～6°).     

Fourier analysis of high-spatial-frequency holographic phase gratings

Plane-wave holograms were recorded on Agfa–Gevaert 8E75HD holographic plates, in a wide range of bias exposures and fringe visibilities. Plates were processed by developer AAC and bleaching agent R-9. Phase gratings were studied by phase-contrast microscopy, using a high-power immersion (100×) objective. Phase-contrast photomicrographs were Fourier analysed. Thus first-, second- and third-order modulations of the refractive index as functions of bias exposure and visibility of the recording interference pattern could be determined. Relative amplitudes of the higher-order modulations to that of the first-order modulation can serve as a measure of the nonlinearity of the holographic recording. The results presented here can be used to check the validity of grating profile calculations based on higher-order coupled-wave theory.     

Aspheric wave-front recording optics for holographic gratings

The geometric theory of aspheric wave-front recording optics is extended to include the fourth-order groove parameters that correspond to the fourth-order holographic terms in the light-path function. We derived explicit expressions of the groove parameters by analytically following an exact ray-tracing procedure for a double-element optical system that consists of a point source, an ellipsoidal mirror, and an ellipsoidal grating blank. Design examples of holographic gratings for an in-plane Eagle-type vacuum-UV monochromator are given to demonstrate the capability of the present theory in the design of aspheric wave-front recording optics.     

用于大尺寸衍射光栅的光刻胶残余物的灰化系统研制

在制作大尺寸厚基底衍射光学元件时,经常需要清除残余底胶,为此我们研制了大尺寸衍射光栅灰化装置.该装置可以在450mm×450mm(φ650mm)范围内产生均匀性良好的等离子体,通过气体辉光放电来达到去残胶的目的,辉光放电速率可通过调节工作气体的浓度来控制.已用该装置灰化处理了200 mm×400mm×50mm的脉宽压缩光栅.     

Concave reflective SU-8 photoresist gratings for flat-field integrated spectrometers

On-chip spectrometry will play a leading role in the development of micro-optofluidic systems for analytical chemistry. Integrated spectrometers fabricated using a polymer-on-silicon platform have been designed, fabricated, and characterized. Reflective grating designs have been implemented using a recursive algorithm to calculate the facet positions as described by McGreer [Appl. Opt. 35, 5904 (1996)]. It is shown that the free spectral range, the output focal plane geometry, and the linear dispersion can be selected with a high degree of control independently of the chosen grating order. The polymer-on-silicon platform facilitates integration with microfluidic circuits and cost-efficient batch fabrication.     

浮雕型全息光栅诱导液晶分子取向排列的研究

在玻璃衬底上制备浮雕型全息光栅作为液晶显示器件取向层,分析了液晶层厚度对液晶分子在光栅取向层上排列的影响.发现液晶层厚度约为8μm时,液晶分子是沿光栅沟槽方向一致排列,其显微织构均匀,各点光强均匀一致,两个相同光强的状态周期为90°,周期性的微沟槽是促使液晶分子取向一致的主要原因.     

Finite-difference-time-domain analysis of finite-number-of-periods holographic and surface-relief gratings

The total-field-scattered-field formulation of the finite-difference time-domain method (FDTD) is used to analyze the diffraction of finite incident beams by finite-number-of-periods holographic and surface-relief gratings. Both second-order and fourth-order FDTD formulations are used with various averaging schemes to treat permittivity discontinuities and a comparative study is made with alternative numerical methods. The diffraction efficiencies for gratings of several periods and various beam sizes, for both TE and TM polarization cases, are calculated and the FDTD results are compared with the finite-difference frequency-domain (FDFD) method results in the case of holographic gratings, and with the boundary element method results in the case of surface-relief gratings. Furthermore, the convergence of the FDTD results to the rigorous coupled-wave analysis results is investigated as the number of grating periods and the incident beam size increase.     

Beam-width-dependent filtering properties of strong volume holographic gratings

The finite dimension of the incident beam used to read out volume holographic gratings has interesting effects on their filtering properties. As the readout beam gets narrower, there is more deviation from the ideal response predicted for monochromatic plane waves. In this paper we experimentally explore beam-width-dependent phenomena such as wavelength selectivities, angular selectivities, and diffracted beam profiles. Volume gratings in both reflection and transmission geometries are investigated near 1550 nm. Numerical simulations utilizing the technique of Fourier decomposition provide a satisfactory explanation and confirm that the spread of spatial harmonics is the main contributing factor.     

Hyperbolic holographic gratings: analysis and interferometric tests

The aberrations of hyperbolic diffraction gratings produced with two spherical waves are analyzed theoretically and experimentally. The behavior of these gratings in collimated illumination indicates that for a grating of a given size there is a critical spatial frequency above which the aberration remains constant for all spatial frequencies. Aberrations associated with geometrical errors in the recording geometry are derived. With simple interferometric tests, misalignments in the recording process can be identified easily.     

Polarization holographic gratings in side-chain azobenzene polyesters with linear and circular photoanisotropy

We investigate thin phase polarization holographic gratings recorded with two waves with orthogonal linear polarizations in materials in which illumination with linearly/circularly polarized light gives rise to linear/circular birefringence. The theoretical analysis shows that the presence of circular photoanisot-ropy changes significantly the diffraction characteristics of the gratings. The intensities of the waves diffracted in the +1 and -1 orders of diffraction and their ratio depend substantially on the reconstructing-wave polarization. Experiments with films of side-chain liquid-crystalline azobenzene polyester that is a photoanisotropic material of the considered type confirm the unusual polarization properties. It is shown that polarization holography may be used for real-time simultaneous measurement of photoinduced linear and circular birefringence.     

Effects of anisotropic diffractions on holographic polymer-dispersed liquid-crystal gratings

Volume gratings fabricated by interferometric exposure using composite materials composed of nematic liquid crystals (LC) and LC diacrylate monomers are discussed in the effects of diffraction properties on different grating formations, such as varying LC content ratios, film thicknesses, and the surface conditions composed of alignment layers and rubbing directions. Diffraction properties are experimentally investigated in the viewpoints of anisotropic diffraction and LC orientation. The polarization-azimuth dependence of diffraction efficiencies as functions of the incident polarization states shows the controllability of anisotropic diffractions based on the effects of different surface conditions.     

High-dispersion spherical holographic gratings in a modified rowland mounting

For holographic gratings requiring an extreme dispersion, I consider a modified Rowland mounting, in which the recording laser sources are moved away from the grating, to reduce the uncorrected higher-order aberrations. In addition, I choose the geometric parameters such that first-type coma is corrected. Then a plane multimode deformable mirror (MDM) or two auxiliary spherical holographic gratings (R3 device) are used to aberrate the grating's recording sources; correction up to the fourth order is sufficient to obtain high image quality. Applied to the FUSE-Lyman (FUSE is Far Ultraviolet Spectroscopic Explorer) grating, with a groove density as high as 5767 grooves/mm, these recording devices produce a resolution (chromatic resolving power) as great as 611,000 with the MDM and 3,030,000 with the R3 device. These results far exceed the specified performance of 30,000. Since diffraction limits the resolution to 482,000, the images are diffraction limited with both devices.