Grating efficiency theory as it applies to blazed and holographic gratings

Development and validation of a cryogenic far-infrared diffraction grating spectrometer used to post-disperse the output from a Fourier transform spectrometer

Recent advances in far-infrared detector technology have led to increases in raw sensitivity of more than an order of magnitude over previous state-of-the-art detectors. With such sensitivity, photon noise becomes the dominant noise component, even when using cryogenically cooled optics, unless a method of restricting the spectral bandpass is employed. The leading instrument concept features reflecting diffraction gratings, which post-disperse the light that has been modulated by a polarizing Fourier transform spectrometer (FTS) onto a detector array, thereby reducing the photon noise on each detector. This paper discusses the development of a cryogenic (4 K) diffraction grating spectrometer that operates over the wavelength range of 285 to 500 μm and was used to post-disperse the output from a room-temperature polarizing FTS. Measurements of the grating spectral response and diffraction efficiency are presented as a function of both wavelength and polarization to characterize the instrumental performance.

Thermal near-field scattering characteristics for dielectric materials

In this study, we passively analyzed the near-field characteristics of thermally excited evanescent waves, which are radiation waves generated by the local dynamics of materials, including electron motions and lattice vibrations. The thermally excited evanescent waves on aluminium nitride (AlN) and gallium nitride (GaN) were measured using passive spectroscopic scattering-type scanning near-field optical microscopy (s-SNOM) in the wavelength ranges of 10.5-12.2 μm and 14.0-15.0 μm, which include the surface phonon-polariton (SPhP) wavelength of the studied dielectrics. We determined the unique decay characteristics of AlN and GaN, indicating a ten-fold increase in the probe area contributing to the scattering of waves near the SPhP wavelength compared to that in other wavelength ranges. The extended probe area correlated with the polariton decay lengths, indicating that the non-enhanced polaritons around K ~ ω/c were dominant in the scattered waves near the SPhP wavelength. In addition to the conventional passive detection mechanisms for metals, the proposed detection scheme will be a versatile passive detection model in the near future.

Chiral liquid crystal based holographic reflective lens for spectral detection

Flat optics based on chiral liquid crystal (CLC) can be achieved using holographic polarization recording with the help of a photoalignment technique to vary the orientation of the optical axis in a thin CLC layer. A variety of reflective diffractive optical components with high efficiency and polarization selectivity can be realized employing this technique. In this work we discuss the use of CLC diffractive lenses in a spectrometer. The functionalities of two mirrors and a linear grating used in a traditional spectrometer are combined into a single holographic CLC component. Circularly polarized light entering through the slit can be reflected and projected onto a linear detector by the CLC component, with over 90% efficiency. This excellent optical functionality can be achieved with a micrometer thin CLC layer, offering the opportunity for device integration.

Progress in the Preparation and Characterization of Convex Blazed Gratings for Hyper-Spectral Imaging Spectrometer: A Review

Convex blazed gratings, which can effectively broaden the spectral range and improve spectral resolution, have gradually evolved into a crucial optical component for lightweight and compact imaging spectroscopy instruments. Their design, processing, and testing involve multidisciplinary interdisciplinary scientific issues, and they continue to be a major area of research in imaging optics applications. This paper summarizes the effects of various grating groove shapes and structural parameters on the spectral range and diffraction efficiency of convex blazed gratings, after providing a brief introduction to the typical functions and applications of convex blazed gratings. Firstly, the latest progress in typical processing methods for convex blazed gratings is reviewed. It focuses on the current fabrication processes and reviews their capabilities in creating convex blazed gratings from three main types of technologies, namely ultra-precision machining, high-energy density beam processing, and chemically assisted fabrication processes. Secondly, the adaptability of the manufacturing process for convex blazed gratings on different scales is summarized, analyzing the adaptation of current procedures to various grating fabrication scales and their bottlenecks. Finally, the characterization methods and future feasible characterization methods for convex blazed gratings are reviewed. The development trend of efficient and precise preparation of convex blazed gratings is pointed out.

High efficiency echelle gratings for the far ultraviolet

Modern grating manufacturing techniques suffer from inherent issues that limit their peak efficiencies. The anisotropic etching of silicon facilitates the creation of custom gratings that have sharp and atomically smooth facets, directly addressing these issues. We describe work to fabricate and characterize etched silicon echelles optimized for the far ultraviolet (FUV; 90-180 nm) bandpass. We fabricate two echelles that have parameters similar to the mechanically ruled grating flown on the Colorado High-resolution Echelle Stellar Spectrograph sounding rocket. We demonstrate a 42% increase in peak order efficiency and an 83% decrease in interorder scatter using these gratings. We also present analysis on where the remaining efficiency resides. These demonstrated FUV echelle improvements benefit the faint source sensitivity and high resolution performance of future UV observatories.

Coloration in Supraparticles Assembled from Polyhedral Metal-Organic Framework Particles

Supraparticles are spherical colloidal crystals prepared by confined self‐assembly processes. A particularly appealing property of these microscale structures is the structural color arising from interference of light with their building blocks. Here, we assemble supraparticles with high structural order that exhibit coloration from uniform, polyhedral metal–organic framework (MOF) particles. We analyse the structural coloration as a function of the size of these anisotropic building blocks and their internal structure. We attribute the angle‐dependent coloration of the MOF supraparticles to the presence of ordered, onion‐like layers at the outermost regions. Surprisingly, even though different shapes of the MOF particles have different propensities to form these onion layers, all supraparticle dispersions show well‐visible macroscopic coloration, indicating that local ordering is sufficient to generate interference effects.

Wavelength beam-combining of terahertz quantum-cascade laser arrays

Wavelength beam-combining of four terahertz (THz) distributed-feedback quantum-cascade lasers (QCLs) is demonstrated using low-cost THz components that include a lens carved out of a plastic ball and a mechanically fabricated blazed grating. Single-lobed beams from predominantly single-mode QCLs radiating peak power in the range of 50-170mW are overlapped in the far field at frequencies ranging from 3.31-3.54THz. Collinear propagation with a maximum angular deviation of 0.3^∘ is realized for the four beams. The total power efficiency for the focused and beam-combined radiation is as high as 25%. This result could pave the way for future commercialization of beam-combined monolithic THz QCL arrays for multi-spectral THz sensing and spectroscopy at standoff distances.

When nanocellulose meets diffraction grating: freestanding photonic paper with programmable optical coupling

Photonic crystals based on plasmonic or dielectric periodic structures have attracted considerable interest owing to their capabilities to control light-matter interactions with tailored precision. By using a nanocellulose derived chiral liquid crystal as a building block, here we demonstrate a bio-inspired dual photonic structure that contains the combination of microscopic periodic 1D surface grating and nanoscopic helical organization, giving rise to programmable colour mixing and polarization rotation. We show that a variation in the photonic band-gap in the bulk matrix leads to simultaneous control over the reflection and diffraction of light with controllable iridescence.

Extreme Asymmetry in Metasurfaces via Evanescent Fields Engineering: Angular-Asymmetric Absorption

On the quest towards full control over wave propagation, the development of compact devices that allow asymmetric response is a challenge. In this Letter, we introduce a new paradigm for the engineering of asymmetry in planar structures, revealing and exploiting unilateral excitation of evanescent waves. We test the idea with the design and experimental characterization of a metasurface for angular-asymmetric absorption. The results show that the contrast ratio of absorption (the asymmetry level) can be arbitrarily engineered from zero to infinity for waves coming from two oppositely tilted angles. We demonstrate that the revealed asymmetry effects cannot be realized using conventional diffraction gratings, reflectarrays, and phase-gradient metasurfaces. This Letter opens up promising possibilities for wave manipulation via evanescent waves engineering with applications in one-side detection and sensing, angle-encoded steganography, flat nonlinear devices, and shaping the scattering patterns of various objects.

Mask aligner lithography using laser illumination for versatile pattern generation

Mask aligner lithography is a well-established back-end fabrication process in microlithography. Within the last few years, resolution enhancement techniques have been transferred and adapted from projection lithography to further develop mask aligner lithography, especially concerning achievable resolution. Nonetheless, current technology using a mercury vapor lamp as a light source has reached its limits, e.g. for high-resolution pattering. Within this paper, we present the extension of the existing mask aligner illumination system by replacing the mercury vapor lamp with a solid-state laser. Full-field mask aligner lithography is guaranteed by a rotating diffuser expanding the laser beam and minimizing undesired speckle effects. An additional integrated galvanometer scanner allows a flexible choice of arbitrary angular spectrum distributions of the photomask illumination. We show versatile results like simple binary patterns of squares and triangles, as well as a more complex lateral shape like a blazed grating.

Blazed wire-grid polarizer for plasmon-enhanced polarization extinction: design and analysis

We explore plasmon-enhanced wire-gird polarizers (WGPs) to achieve improved polarimetric performance with more relaxed fabrication parameters compared to conventional WGP. A WGP designed with a blazed wire-grid profile was considered for plasmonic enhancement. The results show that a blazed WGP can achieve extremely high polarimetric extinction at a longer wire-grid period (Λ) compared to conventional WGP structure. Under the optimum geometrical parameters, a blazed WGP may attain an extinction ratio of over 40 dB at Λ = 800 nm, which may allow photolithography for fabrication. In contrast, conventional WGPs obtained comparable performance at Λ = 200 nm, requiring more difficult lithographic techniques. The study can therefore be of significant importance for WGPs to be more widely available for diverse applications.

Wide-band/angle Blazed Surfaces using Multiple Coupled Blazing Resonances

Blazed gratings can reflect an oblique incident wave back in the path of incidence, unlike mirrors and metal plates that only reflect specular waves. Perfect blazing (and zero specular scattering) is a type of Wood's anomaly that has been observed when a resonance condition occurs in the unit-cell of the blazed grating. Such elusive anomalies have been studied thus far as individual perfect blazing points. In this work, we present reflective blazed surfaces that, by design, have multiple coupled blazing resonances per cell. This enables an unprecedented way of tailoring the blazing operation, for widening and/or controlling of blazing bandwidth and incident angle range of operation. The surface can thus achieve blazing at multiple wavelengths, each corresponding to different incident wavenumbers. The multiple blazing resonances are combined similar to the case of coupled resonator filters, forming a blazing passband between the incident wave and the first grating order. Blazed gratings with single and multi-pole blazing passbands are fabricated and measured showing increase in the bandwidth of blazing/specular-reflection-rejection, demonstrated here at X-band for convenience. If translated to appropriate frequencies, such technique can impact various applications such as Littrow cavities and lasers, spectroscopy, radar, and frequency scanned antenna reflectors.

Single-order transmission diffraction gratings based on dispersion engineered all-dielectric metasurfaces

A single-order transmission diffraction grating based on dispersion engineered all-dielectric metasurfaces is proposed, and its wavelength discriminating properties have been theoretically described and confirmed using numerical simulations. The metasurface is designed using a 2D array of all-dielectric resonators, which emulates a Huygens' source configuration to achieve a perfect match to free space in broad bandwidth. Using a holey dielectric nanodisk structure as the unit cell, the resonant wavelength is tapered across the metasurface to engineer the wavelength-dependent spatial phase gradient, to emulate a dispersive prism. Consequently, different wavelengths are steered toward different directions and thus are discriminated on the output image plane. Due to the subwavelength periodicities involved, wavelength discrimination is achieved directly in the zeroth diffraction order of the device, unlike conventional diffraction gratings, thereby providing a high-efficiency wavelength discriminating device.

Laser microstructured metal thin films as promising alternative for indium based transparent electrodes

In the search for alternative materials to replace indium-tin-oxide in transparent electrodes we have structured copper and aluminum thin films (between 5 an 40 nm) for tailoring their optical properties. Micrometer scaled holes were produced using the direct laser interference patterning (DLIP) technique. We compared the optical and electrical parameters of nanosecond and picosecond processed thin films. It was found that the optical transmittance of the structured layers was relatively increased between 25 to 125% while the electrical resistance was marginally influenced. In addition, the laser treatment enhanced the diffuse to total transmission ratio (HAZE) by values ranging from 30 to 82% (relative) as a potential advantage of μm structuring. The results also show that both of the studied metals succeed to match the target which is set by typical applications of indium thin oxide (ITO) films. Furthermore, numerical simulations are performed in order to understand the ablation process of thin film material for ps and ns pulses.

CW 50W/M2 = 10.9 diode laser source by spectral beam combining based on a transmission grating

An external cavity structure based on the -1st transmission grating is introduced to spectral beam combining a 970 nm diode laser bar. A CW output power of 50.8 W, an electro-optical conversion efficiency of 45%, a spectral beam combining efficiency of 90.2% and a holistic M(2) value of 10.9 are achieved. This shows a way for a diode laser source with several KW power and diffraction-limited beam quality at the same time.

Analysis of a color-matching backlight system using a blazed grating and a lenticular lens array

A high efficiency LCD employing a color-matching backlight system that consists of a collimation lenticular lens sheet, a blazed grating, and a focusing lenticular lens array is proposed and analyzed. The RGB lights that are collimated and dispersed from the collimation lenticular lens sheet and the blazed grating are incident on the RGB color filters by the focusing lenticular lens array. The color-matched transmittance was increased 183% and 121% for divergence angles of 2° and 11°, respectively, compared to a conventional backlight that does not use a blazed grating. The design, simulation, and experimental results for the prototype color-matching backlight system are presented.

Angularly separated harmonic generation from intense laser interaction with blazed diffraction gratings

We made numerical simulations of the generation of narrowband beams of extreme ultraviolet radiation from intense laser interaction with a blazed grating surface. Strong fifth harmonic emission into its blazed diffraction order was observed as well as heavy suppression of the fundamental frequency with comparison to a typical harmonic spectrum from a flat target. The results demonstrate a new highly efficient method of generating near-monochromatic harmonics from the fundamental with minimal effect on the pulse duration.

Confocal fluorescence polarization microscopy for linear unmixing of spectrally similar labels

Studies of biological samples often call for simultaneous identification of multiple molecular or structural components. Multiple labelling fluorescence techniques are a powerful way of achieving this. However, the ability to distinguish a number of fluorescent probes unambiguously can be restricted by the fact that fluorescence spectra are generally broad and overlapping. Recently a technique known as linear unmixing has been combined with spectral imaging to discriminate between multiple fluorophores. In this study a scheme is proposed whereby fluorescence polarization information is used to expand the capability of the linear unmixing technique to accommodate additional fluorescent probes. As a proof-of-concept, it is shown that this polarization-based technique can be used to divide the signals generated by two spectrally similar fluorescent probes into their separate components.

Reduction of polarization-induced artifacts in grating-based spectrometers

An optical device that converts unpolarized light into a single polarization state is described. The device is based on a polarizing beam splitter that separates the two polarization directions. The beam splitter is combined with two pairs of equilateral prisms that are used to collimate the two beams in terms of both propagation and polarization directions. When it is used in combination with a blazed diffraction grating, this device is shown to effectively remove the polarization dependence of the first-order diffracted power. The device has an insertion loss of approximately 14% for purely s-polarized light. However, for unpolarized light incident upon the two gratings studied here, the increased throughput of the p-polarized component leads to an average relative gain in overall efficiency of 13%-19%, depending on the grating. In collimating the two polarization directions, the device may cause a reduction in spectral resolution for a rectangular entrance slit. As a result, the device is more likely to find use in spectrometers that have a circular aperture, such as that provided by an optical fiber.

Tuning of external-cavity semiconductor lasers with chirped diffraction gratings

We present a novel scheme of tunable semiconductor laser based on the use of a chirped grating in an external cavity. The chirped grating is fabricated using a simple holographic technique: two Gaussian beams having wavefronts with different radii of curvature are brought to interfere on a photoresist layer. The tuning properties of chirped gratings have been investigated with semiconductor lasers operated with an external cavity. With this type of grating positioned in Littrow configuration, the wavelength selection can be done by translating the grating without any need to rotate it. This cavity configuration provides a tunable output beam with an angle of propagation that is independent of the wavelength. The translation of chirped gratings was shown to tune a visible diode laser and an infrared diode laser over the same spectral band as the conventional tuning scheme where an unchirped grating is rotated.

Spectrally narrowed external-cavity high-power stack of laser diode arrays

We describe an effective external cavity for narrowing the spectral linewidth of a multiarray stack of laser diode arrays. For a commercially available 279-W free-running five-array laser diode array operating at 60 A, we narrow the spectral linewidth to 0.40 nm at FWHM with 115 W of cw power output. This technique leads to the possibility of higher-efficiency, lower-cost production of hyperpolarized noble gases for magnetic resonance imaging.

Modulation light efficiency of diffractive lenses displayed in a restricted phase-mostly modulation display

We present an analysis of the diffraction efficiency of diffractive lenses displayed on spatial light modulators that depends on the modulation response of the display. An ideal display would produce continuous phase-only modulation, reaching a maximum phase-modulation depth of 2pi. We introduce the concept of modulation diffraction efficiency that accounts for the effect of nonlinearities only in the phase modulation of the display. We review a diffractive model with which to evaluate this modulation efficiency, including modulation defects such as nonlinear phase modulation, coupled amplitude modulation, phase quantization, and a limited modulation depth. We apply this diffractive model to Fresnel lenses and show that these modulation defects produce a lens multiplex effect. Finally we demonstrate that the application of a minimum Euclidean projection principle leads to high modulation diffraction efficiency even if the phase-modulation depth is much less than 2pi. We demonstrate that the modulation efficiency can exceed 90% for a modulation depth of 1.4pi and can exceed 40% (the equivalent for a binary phase element) for a modulation depth of only 0.7pi. Experimental results from use of a twisted nematic liquid-crystal display are presented to confirm these conclusions.

Single-longitudinal-mode optical parametric oscillator for spectroscopic applications

We have developed a tunable, narrow-bandwidth nanosecond optical parametric oscillator system and applied it to spectroscopic studies. The system consists of a narrow-bandwidth grazing-incidence oscillator and a seeded power oscillator, generating Fourier-transform-limited 1.5-ns pulses (bandwidth <500 MHz) in the wavelength range 435 to 2000 nm with energy of 3.5 mJ at a pump energy of 22 mJ. Continuous scanning over 30 to 100 GHz (depending on wavelength) is demonstrated by recording of the resonance line of the Hg atom at 253.7 nm and a vibrational transition of the CO (2) molecule at 1528 nm.

Observation of optical Smith-Purcell radiation at an electron beam energy of 855 MeV

Smith-Purcell radiation, generated when a beam of charged particles passes close to the surface of a diffraction grating, has been studied in the visible spectral range at wavelengths of 360 and 546 nm with the low emittance 855 MeV electron beam of the Mainz Microtron MAMI. The beam focused to a spot size of 4 microm (full width at half maximum) passed over optical diffraction gratings of echelle profiles with blaze angles of 0.8 degrees, 17.27 degrees, and 41.12 degrees and grating periods of 0.833 and 9.09 microm. Taking advantage of the specific emission characteristics of Smith-Purcell radiation a clear separation from background components, such as diffracted synchrotron radiation from upstream beam optical elements and transition radiation, was possible. The intensity scales with a modified Bessel function of the first kind as a function of the distance between electron beam and grating surface. Experimental radiation factors have been determined and compared with calculations on the basis of Van den Berg's theory [P.M. Van den Berg, J. Opt. Soc. Am. 63, 689 (1973)]. Fair agreement has been found for gratings with large blaze angles while the measurement with the shallow grating (blaze angle 0.8 degrees ) is at variance with this theory. Finally, the optimal operational parameters of a Smith-Purcell radiation source in view of already existing powerful undulator sources are discussed.

Mode-hop-free electro-optically tuned diode laser

A tunable external-cavity Littrow diode laser, with an intracavity electro-optical crystal, which combines a large mode-hop-free tuning range with high tuning speeds and high tuning accuracy, has been designed. A mode-hop-free single-mode tuning range of 50 GHz at 793 nm with an output power of 60 mW and tuning speeds of 1.5 GHz/micros is demonstrated. The instantaneous linewidth is smaller than 300 kHz. Generally mode-hop-free tuning is obtained when the elongation of the cavity is proportional to the cavity length measured anywhere across the beam. This elongation is achieved with an intracavity crystal in which the thickness, and thus the electric field inside it, varies across the beam.

Free-space wavelength-multiplexed optical scanner

A wavelength-multiplexed optical scanning scheme is proposed for deflecting a free-space optical beam by selection of the wavelength of the light incident on a wavelength-dispersive optical element. With fast tunable lasers or optical filters, this scanner features microsecond domain scan setting speeds and large- diameter apertures of several centimeters or more for subdegree angular scans. Analysis performed indicates an optimum scan range for a given diffraction order and grating period. Limitations include beam-spreading effects based on the varying scanner aperture sizes and the instantaneous information bandwidth of the data-carrying laser beam.

Ultraviolet groove efficiency of a holographic grating: implications for a dual-order spectrograph

The ultraviolet groove efficiency for a holographically ruled diffraction grating with a trapezoidal profile has been measured. The efficiencies for the +/-1 and the zero orders are in good agreement with those derived from scalar theory. The +/-1 orders have equal efficiency as a function of wavelength. The peak of the sum of fitted groove efficiency functions is 76%, a level that is competitive with the groove efficiency of a mechanically blazed grating. We suggest that a normal-incidence grating mount with detectors at both orders will offer a system with twice the efficiency and provide a built-in redundancy. We discuss design considerations for reducing astigmatism equally in both orders in such dual-order mountings.

Two-channel tunable monochromatic illuminator with a concave diffraction grating and an original scanning system

A two-channel monochromatic illuminator with only one diffraction grating and an original scanning system has been designed for multiple applications. This scanning system consists of two rotational plane mirrors that reflect light diffracted by a concave diffraction grating to the ?1 orders of the spectrum. The light reflected by the mirrors goes to two exit slits that correspond to two channels of the device. The positions of the centers of rotation of the mirrors are selected to produce minimal deviation of the direction of the light reflected during the scanning. The aberration characteristics of some variations in the optical mounting of the device made by use of spherical and toroidal holographic diffraction gratings recorded in stigmatic and astigmatic beams, the possibilities for application of the device for measuring the color sensitivity of the human eye, and the possibilities for measuring the efficiency of concave diffraction gratings, are also discussed.

Rigorous coupled-wave analysis for practical planar dielectric gratings: 2. Diffraction by a surface-eroded hologram layer

The diffraction efficiencies of practical dielectric holograms are evaluated with rigorous coupled-wave analysis. The cases of the hologram surfaces eroded in several shapes are treated and compared with those in which the surfaces are not eroded and with those in which there are only surface gratings. Eroding the surface will increase the higher-order reflection diffraction efficiencies and the transmissions, thus reducing the first reflection and the zeroth transmission. However, sealing the hologram with a cover plate, as is done in manufacturing many holograms, extinguishes the erosion effect.

Comparison of the calculated and the measured efficiencies of a normal-incidence grating in the 125-225- A wavelength range

The efficiency of a diffraction grating was measured near normal incidence in the 125-225-A wavelength range with synchrotron radiation. The grating pattern had 2400 grooves/mm and was recorded on a concave fused-silica blank by a holographic technique. The grooves were shaped by ion-beam etching to provide a facet with a blaze angle of 2.5 degrees as determined by atomic force microscopy. Because of the characteristics of the etching process the groove profile was approximately triangular, with the other facet inclined at an angle of 5.5 degrees to the surface. The measured efficiency was compared with the efficiency calculated by a computer program, small enough to run on a personal computer, that solved the periodic boundary-value problem corresponding to electromagnetic radiation incident on a diffraction grating with finite conductivity. The calculation was based on the nominal groove profile that was determined by atomic force microscopy. The measured and the calculated efficiencies were in good agreement. This investigation indicates that the diffraction efficiency of a normal-incidence grating can be calculated in the soft-x-ray region with a personal computer.

High-efficiency metallic diffraction gratings for laser applications

The design and fabrication of large-area, high-efficiency metallic gratings for use in high-power laser systems is described. The gratings exhibit a diffraction efficiency in excess of 95% in the m = -1 order (Littrow mount) and have a high threshold for laser damage. Computations and experimental measurements are presented that illustrate the effect of grating shape and polarization on efficiency. A simple theory for optical damage to metallic diffraction gratings is developed and compared with experimental measurements of the laser-damage threshold over the pulse range from 400 fs to >1 ns.

Tunable external cavity diode laser that incorporates a polarization half-wave plate

The threshold current and specttal properties of a grating tuned external cavity semiconductor laser are improved by utilizing an intracavity half-wave plate to optimize the grating feedback.

Effects of diffraction efficiency on the modulation transfer function of diffractive lenses

Diffractive lenses differ from conventional optical elements in that they can produce more than one image because of the presence of more than one diffraction order. These spurious, defocused images serve to lower the contrast of the desired image. We show that a quantity that we define as the integrated efficiency serves as a useful figure of merit to describe diffractive lenses. The integrated efficiency is shown to be the limiting value for the optical transfer function; in most cases it serves as an overall scale factor for the transfer function. We discuss both monochromatic and polychromatic applications of the integrated efficiency and provide examples to demonstrate its utility.

Holographic Fourier diffraction gratings with a high diffraction efficiency optimized for optical communication systems

Novel diffraction gratings in a near-infrared region that is specially optimized for optical communication systems are studied and demonstrated by using a simple holographic exposure process. These gratings have a unique groove profile. The gratings of 770 lines/mm have a very high efficiency of 95% at a wavelength of 1.31 microm and more than 85% at a wavelength of 1.52 microm for nonpolarized light in the Littrow mounting. They also show a very low dependence (less than 2%) of the efficiency on the polarization.

Electromagnetic study of transmission gratings

The performances of triangular groove photoresist gratings used in transmission are studied in the visible and near-infrared regions with the electromagnetic theory. The mounting considered here associates triangular groove gratings on the hypotenuse face of a right-angle prism in a configuration, usually called a grism, in such a way that for a chosen wavelength the deviations of the prism and the grating compensate. To assist designers of spectrometric systems, we have covered a complete range of blaze wavelengths and, consequently, of blaze angles. We studied the influence on grating efficiencies when the line density is increased, and the optimal choice angle of incidence is discussed.

Intensity calibration of an EUV polarizer spectrometer detector system

The absolute transmission and polarization of a polarizer and a Seya-Namioka monochromator are measured in the 50-120-nm wavelength range using spectrally dispersed synchrotron radiation. Grating illumination, astigmatism, and higher-order diffraction are taken into account. The efficiency of a channel electron multiplier is determined relative to a NBS calibrated A1(2)O(3) photodiode. The instruments are studied separately. The results are compared to other experimental and theoretical data where possible.

Asymmetrical trapezoidal grating efficiency

The diffraction efficiency behavior of reflection gratings with an asymmetrical trapezoidal groove profile has been studied. Theoretical calculations predict that at certain grating parameters superior efficiency compared to the conventional ruled gratings can be achieved.

Hinge spectrometer: a grating Fabry-Perot instrument for far-infrared/submillimeter spectroscopy in space

A compact submillimeter spectrometer can be constructed through the use of a combination of grating and Fabry-Perot techniques. The instrument has only one moving part, a grating that pivots about an accurately placed hinge. The entire optical train is cooled to liquid helium temperature for low-background low-noise operation and is designed for use in astronomical observations from aircraft, balloons, or space vehicles. Resolving power R ~ 20,000 at ~ 150microm is demonstrated.

Asymmetric triangular grating profiles with 90 degrees groove angles produced by ion-beam erosion

A simple phenomenological model has been developed to account for the effects of redeposition during transverse ion-beam erosion of grating relief patterns on surfaces. The model predicts the evolution with time of an inclined facet in the substrate, and the dependence of the facet angle theta(r) on angle of incidence of the ion beam, erosion rates of mask and substrate, and the geometrical parameters of the mask. The results are illustrated by calculation of the angular dependence of theta(r) for AZ-1350 photoresist masks on GaAs and SiO(2) substrates and for Ti on SiO(2). A strong dependence of theta(r) on mask intercept angle alpha is found, except for a limited range in angle of incidence of the ion beam. Combined with results derived previously, the facet angles theta(S) and theta(r) and the groove angle theta(g) of the asymmetric triangular groove profiles produced in these systems have been determined. A groove angle of 90 degrees cannot be obtained for AZ-1350 on GaAs and SiO(2), but in appropriate conditions a 90 degrees groove angle may be obtained in SiO(2) with a Ti mask.

Absolute S- and P-plane polarization efficiencies for high frequency holographic gratings in the VUV

High frequency plane gratings (3500 and 3600 gr/mm) have been holographically ruled and blazed for the VUV spectral region. All gratings were coated with 70 nm Al + 25 nm MgF(2). Absolute unpolarized and S-and P-plane polarization efficiencies have been measured for the first and second orders in the 120- to 450 -nm spectral region at 18.5 and 30 degrees angles of deviation. For deep grooves, anomalous features are more pronounced for the P-plane polarization efficiency than for the S-plane polarization efficiency. Holographic gratings can be tailored to produce high polarization or low polarization in the VUV. For comparison, efficiencies and polarization of the best conventional high frequency gratings were also determined. Measurements show that scattered light is significantly lower for holographic gratings in the VUV when compared with the conventional gratings.