Showing papers on "Diffraction efficiency published in 2009"
TL;DR: A technique is proposed theoretically and verified experimentally to eliminate a zero-order beam caused by a pixelated phase-only spatial light modulator (SLM) for holographic projection that results in higher reconstruction quality and diffraction efficiency.
Abstract: A technique is proposed theoretically and verified experimentally to eliminate a zero-order beam caused by a pixelated phase-only spatial light modulator (SLM) for holographic projection. The formulas for determination of the optical field in the Fourier plane are deduced, and the influence of the pixelated structure of a SLM on the intensity of the zero-order beam is numerically investigated. Two currently existing techniques are studied and a new one is presented. These three techniques are used separately to eliminate the zero-order interruption, and the optical performances of the reconstructed patterns are compared. The new technique results in higher reconstruction quality and diffraction efficiency. A short animated movie is illuminated for holographic projection display. The experimental results show that the zero-order beam can be efficiently eliminated by the new technique. It is believed that this technique can be used in various optical systems that are based on pixelated phase-only SLMs, such as holographic optical tweezers and optical testing systems.
156 citations
TL;DR: In this paper, a systematic study of Bloch surface wave (BSW) properties and applications in diffraction-based biosensors is presented, in which polarization and 1DPC termination effects are simply described.
Abstract: A systematic study of Bloch surface wave (BSW) properties and applications in diffraction-based biosensors is presented. The design of such devices starts with the calculation of the BSW dispersion relation for a semi-infinite one-dimensional photonic crystal. We propose an approach in which polarization and 1DPC termination effects are simply described. Since in a realistic device the number of periods is limited, we investigate the issues arising from finite size effects and the choice of a structure substrate. Diffraction efficiency is studied as a function index contrast, multilayer termination, grating thickness, and number of periods. Numerical examples for Si/SiO2 and a-Si1−xNx:H periodic dielectric stacks are presented, showing that BSW can be exploited for the realization of efficient diffraction-based biosensors from the infrared to the visible range.
118 citations
Patent•
IBM1
TL;DR: In this paper, a dispersive element includes resin members for forming a diffraction grating, being composed of a plurality of diffraction gating members having a cross-sectional shape respectively surrounded by two straight lines such as a triangular shape.
Abstract: In a transmission grating as a dispersive element, diffraction efficiency is enhanced and manufacturing costs are considerably reduced. A dispersive element includes resin members for forming a diffraction grating, being composed of a plurality of diffraction grating members having a cross-sectional shape respectively surrounded by two straight lines such as a triangular shape, and metal members as light-shielding members each being formed on corresponding one of the diffraction grating members at one side of the diffraction grating member along any of the straight line and the curved line of the cross-sectional shape of the diffraction grating member formed by the resin member. The metal members are configured to reduce zero-order transmitted light with respect to incident light, and to enhance diffraction efficiency of first-order transmitted light.
106 citations
TL;DR: The ability of optical axis gratings (OAGs) to fully transfer the energy of an unpolarized incident light beam into the ± 1st diffraction orders is explored in this paper for development of a polarization-independent optical system with nonlinear transmission.
Abstract: The ability of optical axis gratings (OAGs) to fully transfer the energy of an unpolarized incident light beam into the ±1st diffraction orders is explored below for development of a polarization-independent optical system with nonlinear transmission Diffractive properties of OAGs based on azo dye doped liquid crystals (azo LCs) are efficiently controlled with low power radiation Switching from diffractive to transmissive states of the OAG takes place within 50 ms at 60 W/cm2 power density level, while the diffractive state is restored within ~ 1 s in the absence of radiation High contrast optical switching is demonstrated with violet as well as green laser beams A photoswitchable OAG is paired with a light-insensitive OAG in diffraction compensation configuration to obtain an optical system switchable from high to low transmission state The thinness of OAGs required for high contrast switching ensures high overall transmission of the system Given also the spectrally and angularly broadband nature o
105 citations
TL;DR: It is demonstrated that they can be combined for polarization-insensitive imaging and optical switching applications and a pair of closely spaced, parallel oriented, cycloidal polarization gratings is capable of canceling the diffractive property of an individual grating.
Abstract: Liquid crystal polarization gratings exhibit high diffraction efficiency (~ 100%) in thin material layers comparable to the radiation wavelength. We demonstrate that they can be combined for polarization-insensitive imaging and optical switching applications. A pair of closely spaced, parallel oriented, cycloidal polarization gratings is capable of canceling the diffractive property of an individual grating. As a result, the phase of the beam is not distorted, and holographic images can be formed through them. An anti-parallel arrangement results in a broader effective diffraction band and doubles the diffraction angle. Broadband diffraction spanning from 480 nm to beyond 900 nm wavelengths has been obtained for a pair of gratings with 500 nm and 633 nm peak diffraction wavelengths. Liquid crystal polymer cycloidal gratings were used in the study showing 98% diffraction efficiency over a large area, and allowed for the use of laser beams expanded to 25 mm. The characteristics of combined cycloidal gratings were tested with laser beams at both UV and red wavelengths.
87 citations
TL;DR: A holographically fabricated, optically switchable grating using azo-dye-doped, polymer-dispersed liquid crystals (LCs) is reported, showing that upon photoirradiation, the diffraction of the grating was decreased significantly.
Abstract: We report a holographically fabricated, optically switchable grating using azo-dye-doped, polymer-dispersed liquid crystals (LCs). Our experiments show that upon photoirradiation, the diffraction of the grating was decreased significantly. We believe that this switching behavior is due to two factors--nematic-isotropic phase transition of LCs and thermal expansion of the grating structure.
76 citations
TL;DR: It is demonstrated that surface-relief gratings with modulation depth of up to 440 nm can be inscribed through the use of hydrogen bonding between the polymer and the chromophores, which simplifies the preparation process compared to covalent functionalization while still being strong enough to induce macroscopic motions of the polymer chains.
Abstract: We show that efficient photoinduced surface-relief gratings can be inscribed in polymer-azobenzene complexes which are bonded by phenol-pyridine hydrogen bonding The grating inscription was studied as a function of chromophore concentration and the molecular weight of the host polymer, both of which can be easily tuned without demanding organic synthesis Stable gratings with modulation depth as high as 440 nm and with diffraction efficiency exceeding 40% were inscribed in the equimolar complexes Our results demonstrate that phenol-pyridine hydrogen bonding not only allows one to increase the chromophore content until each polymer unit is occupied but is also sufficiently strong to induce mass migration of the polymer chains in a manner comparable to covalently functionalized polymers
74 citations
TL;DR: A novel digital holographic algorithm, correcting optical system imaging, is developed that uses plane wave spectrum decomposition of optical field for solving diffraction problem between parallel and tilted planes and enabling correction of imaging system aberrations.
Abstract: In the paper the optical diffraction tomographic system for reconstruction of the internal refractive index distribution in optical fiber utilizing grating Mach-Zehnder interferometer configuration is explored. The setup applies afocal imaging. Conventional grating application gives, however, highly aberrated object beam producing incorrect refractive-index reconstructions. The grating inherent aberrations are characterized, its influence on both image projections and refractive index reconstructions is presented. To remove aberrations and enable tomographic reconstruction a novel digital holographic algorithm, correcting optical system imaging, is developed. The algorithm uses plane wave spectrum decomposition of optical field for solving diffraction problem between parallel and tilted planes and enabling correction of imaging system aberrations. The algorithm concept was successfully proved in simulations and the experiment.
71 citations
TL;DR: In this paper, it was shown that the paraxial diffraction can be eliminated by using atomic diffusion to influence the spreading of the image, regardless of its position and shape.
Abstract: Electromagnetically induced transparency in an atomic gas can slow the propagation of images. It is now shown that the diffraction of such images as they propagate can be controlled and even eliminated. This is achieved by using atomic diffusion to influence the spreading of the image. Any image, imprinted on a wave field and propagating in free space, undergoes a paraxial diffraction spreading. The reduction or manipulation of diffraction is desirable for many applications, such as imaging, wave-guiding, microlithography and optical data processing. As was recently demonstrated, arbitrary images imprinted on light pulses are dramatically slowed1,2 when traversing an atomic medium of electromagnetically induced transparency3,4 and undergo diffusion due to the thermal atomic motion5,6. Here we experimentally demonstrate a new technique to eliminate the paraxial diffraction and the diffusion of slow light, regardless of its position and shape7. Unlike former suggestions for diffraction manipulation8,9,10,11,12, our scheme is linear and operates in the wavevector space, eliminating the diffraction for arbitrary images throughout their propagation. By tuning the interaction, we further demonstrate acceleration of diffraction, biased diffraction and induced deflection, and reverse diffraction, implementing a negative-diffraction lens13. Alongside recent advances in slow-light amplification14 and image entanglement15, diffraction control opens various possibilities for classical and quantum image manipulation.
66 citations
TL;DR: The quality of polarization gratings imprinted with linear polarized light is as high as that of gratings obtained in the holographic process, while exhibiting twice larger diffraction angle.
Abstract: We provide detailed description and characterization of specifics of the imprinting technique for fabrication of large-area and high-efficiency liquid crystal polymer polarization gratings. We show that the quality of polarization gratings imprinted with linear polarized light is as high as that of gratings obtained in the holographic process, while exhibiting twice larger diffraction angle. The cycloidal polarization pattern used for imprinting is obtained from a master polarization grating, and the importance of fine tuning of its peak diffraction wavelength to the wavelength of imprinting radiation is emphasized. Tuning of the peak diffraction wavelength of imprinted polarization gratings from UV to near IR was realized with the aid of multilayer structures. Since the imprinting process does not involve a holographic setup, it is insensitive to ambient conditions and vibrations and provides an opportunity for large scale production of polarization gratings.
59 citations
TL;DR: The mechanism of achieving unidirectional transmission in the gratings, which only contain isotropic dielectric and metallic layers, is suggested and numerically validated and is expected to become an alternative to that based on the use of anisotropic materials.
Abstract: The mechanism of achieving unidirectional transmission in the gratings, which only contain isotropic dielectric and metallic layers, is suggested and numerically validated. It is shown that significant transmission in one direction and nearly zero transmission in the opposite direction can be obtained in the same intrinsically isotropic gratings as those studied recently in A. E. Serebryannikov and E. Ozbay, Opt. Express 17, 278 (2009), but at a non-zero angle of incidence. The tilting, non-symmetric features of the grating and the presence of a metallic layer with a small positive real part of the index of refraction are the conditions that are necessary for obtaining the unidirectionality. Single- and multibeam operational regimes are demonstrated. The frequency and angle ranges of the unidirectional transmission can be estimated by using the conventional framework based on isofrequency dispersion contours and construction lines that properly take into account the periodic features of the interfaces, but should then be corrected because of the tunneling arising within the adjacent ranges. After proper optimization, this mechanism is expected to become an alternative to that based on the use of anisotropic materials.
TL;DR: In this article, a binary diffractive optical element (1500 × 1500 × 1500 pixels, diameter 4.5mm) is designed by partial encoding and fabricated by direct electron beam writing in SiO2.
Abstract: A binary diffractive optical element (1500 pixels × 1500 pixels, diameter 4.5 mm) is designed by partial encoding and fabricated by direct electron beam writing in SiO2. Two conjugate hyper-geometric laser modes are generated using the fabricated element. The root-mean-square transverse intensity deviation of the experimental from theoretical diffraction pattern, determined within a circle of radius 1 mm, is below 13%.
TL;DR: This work has demonstrated broad bandwidth large area multilayer dielectric diffraction gratings for the efficient compression of high energy 800 nm laser pulses at high average power.
Abstract: We have demonstrated broad bandwidth large area (229 mm x 114 mm) multilayer dielectric diffraction gratings for the efficient compression of high energy 800 nm laser pulses at high average power. The gratings are etched in the top layers of an aperiodic (Nb0.5Ta0.5)2O5-SiO2 multilayer coating deposited by ion beam sputtering. The mean efficiency of the grating across the area is better than 97% at the center wavelength and remains above 96% at wavelengths between 820 nm and 780 nm. The gratings were used to compress 5.5 J pulses from a Ti:sapphire laser with an efficiency above 80 percent.
TL;DR: It is shown that it is possible to achieve diffractive gratings with diffraction efficiency in the first order near 35% if the in dark evolution is taken into account and a method to calculate the monomer diffusivity in photopolymers is presented.
Abstract: Molecular diffusion effects have been widely studied inside photopolymers for holographic applications. Recently some works have focused on low spatial frequencies to evaluate in real time the monomer diffusion effects. Assuming a Fermi-Dirac function-based profile, we have fitted the diffracted intensities, reflected and transmitted (up to the 8th order), to obtain the phase and surface profile of the recorded gratings. We have studied the influence of diffusion in polyvinyl-alcohol/acrylamide for the range of spatial frequencies between 2 lines/mm and 6 lines/mm. We have demonstrated the influence of the spatial frequency on the magnitude and sign of the material volume variations. We also studied in dark the evolution of the grating shape. We show that it is possible to achieve diffractive gratings with diffraction efficiency in the first order near 35% if the in dark evolution is taken into account. Furthermore we present a method to calculate the monomer diffusivity in photopolymers. The differential equation is deduced and solved, and experimental average value is obtained (D=1.1·10−8 cm2s−1).
TL;DR: In this paper, the room temperature, water-cooled, diode pumped Tm:YLF laser head was elaborated and examined for pumping the fiber coupled (0.2 mm core diameter) 25-W laser diode bar emitting at 792-nm wavelength.
Abstract: The room-temperature, water-cooled, diode pumped Tm:YLF laser head was elaborated and examined. For pumping the fiber coupled (0.2 mm core diameter) 25-W laser diode bar emitting at 792-nm wavelength was deployed. Near 5 W of CW output power and 25% slope efficiency was demonstrated in a short, 70-mm long resonator. Tuning in 1845–1935 nm wavelength range by means of 2-plate Lyot filter was demonstrated only in free-running regime. The fused silica acousto-optic modulator with above 80% diffraction efficiency for 25-W power of RF was deployed as the Q-switch for such a laser. In the best case of Q-switching regime, up to 10-mJ output energy with 47-ns pulse duration, 220 kW peak power was demonstrated for 133 Hz. For higher repetition rate of 2 kHz, 12 kW peak power with 2.5 W of average power was achieved.
TL;DR: In this article, a reflectivemode liquid crystal polarization grating with high reflectance, small grating period, and sub-ms switching times is presented, which can diffract ∼100% into a single order, have highly polarization-sensitive first orders, and have a polarization-insensitive zero order.
Abstract: We experimentally demonstrate a reflective-mode liquid crystal polarization grating with high reflectance, small grating period, and subms switching times. This switchable optical element can diffract ∼100% into a single order, have highly polarization-sensitive first orders, and have a polarization-insensitive zero order. Here we introduce an absorbing layer that overcomes the reflection of the (ultraviolet) holographic beams, which otherwise prevents high quality fabrication. At a grating period of 2.1 μm, we report 98% diffraction efficiency, 90% reflectance, ∼600:1 contrast-ratio, and ∼3000:1 polarization contrast. These elements can therefore be configured as polarization-independent modulators or switchable polarizing beam splitters, for use in telecommunications, displays, spatial-light modulators, and polarimetry.
TL;DR: An experimental investigation of high reflection mirrors used to fabricate gratings for pulse compression application at the wavelength of 1.053microm evidences that MMLD design can offer damage performances rather similar to MLD design, it also exhibits lower stresses; being thus an optimal mirror substrate for a pulse compression grating operating under vacuum.
Abstract: We report an experimental investigation of high reflection mirrors used to fabricate gratings for pulse compression application at the wavelength of 1.053microm. Two kinds of mirrors are studied: the mixed Metal MultiLayer Dielectric (MMLD) mirrors which combine a gold metal layer with some e-beam evaporated dielectric bilayers on the top and the standard e-beam evaporated MultiLayer Dielectric (MLD) mirrors. Various samples were manufactured, damage tested at a pulse duration of 500fs. Damage sites were subsequently observed by means of Nomarski microscopy and white light interferometer microscopy. The comparison of the results evidences that if MMLD design can offer damage performances rather similar to MLD design, it also exhibits lower stresses; being thus an optimal mirror substrate for a pulse compression grating operating under vacuum.
TL;DR: This paper presents the first experimental demonstration on the holographic fabrication approach of three-dimensional photonic crystal templates with functional defects by a single laser exposure using a single optical element.
Abstract: This paper demonstrates an approach for laser holographic patterning of three-dimensional photonic lattice structures using a single diffractive optical element. The diffractive optical element is fabricated by recording gratings in a photosensitive polymer using a two-beam interference method and has four diffraction gratings oriented with four-fold symmetry around a central opening. Four first-order diffracted beams from the gratings and one non-diffracted central beam overlap and form a three-dimensional interference pattern. The phase of one side beam is delayed by inserting a thin piece of microscope glass slide into the beam. By rotating the glass slide, thus tuning the phase of the side beam, the five beam interference pattern changes from face-center tetragonal symmetry into diamond-like lattice symmetry with an optimal bandgap. Three-dimensional photonic crystal templates are produced in a photoresist and show the phase tuning effect for bandgap optimization. Furthermore, by integrating an amplitude mask in the central opening, line defects are produced within the photonic crystal template. This paper presents the first experimental demonstration on the holographic fabrication approach of three-dimensional photonic crystal templates with functional defects by a single laser exposure using a single optical element.
TL;DR: By applying the most efficient polarization configuration in combination with the best material, this paper was able to reach modulation heights of up to 600 nm, which is a factor of 2 higher than modulations usually reported for azobenzene-containing polymers.
Abstract: This paper presents a comprehensive study of the formation of surface relief gratings in a series of photoresponsive molecular glasses. Holographic experiments were performed on films of the azobenzene-containing molecular glasses. Seven relevant polarization configurations of the writing beams were systematically applied, and simultaneously the diffraction efficiency was monitored during the process of inscription. The temporal evolution of the diffraction efficiency can be precisely simulated with a model which takes both the surface relief and the phase grating in the volume into account. From the measured diffraction efficiencies, the modulation heights can be directly calculated and they were independently confirmed by atomic force microscopy. We found that all experimental results can be explained with the gradient force model, and we suggest that the grating heights generated with different writing polarizations can be ascribed to the varying strengths of the gradient force. For materials with different substituents at the azobenzene chromophore, the optical susceptibility at the writing laser wavelength and, therefore, the gradient force varies. By applying the most efficient polarization configuration in combination with the best material, we were able to reach modulation heights of up to 600 nm, which is a factor of 2 higher than modulations usually reported for azobenzene-containing polymers.
TL;DR: In this paper, the fabrication of centimeter-size transmission Bragg gratings in semiconductor CdSe quantum dots dispersed 50 μm thick photopolymer films was reported.
Abstract: We report on the fabrication of centimeter-size transmission Bragg gratings in semiconductor CdSe quantum dots dispersed 50 μm thick photopolymer films. This was done by holographic assembly of CdSe quantum dots in a photopolymerizable monomer blend. Periodic patterning of CdSe quantum dots in polymer was confirmed by a fluorescence microscope and confocal Raman imaging. The diffraction efficiency from the grating of 1 μm spacing was near 100% in the green with 0.34 vol % CdSe quantum dots, giving the refractive index modulation as large as 5.1×10−3.
TL;DR: In this paper, a new type of high efficiency grating coupler based on single crystalline Si nanomembrane overlay and stacking was designed for the purpose of coupling light between single mode fibres and nanophotonic waveguides, and for the coupling between multiple photonic interconnect layers for compact three-dimensional vertical integration.
Abstract: We report here the design of a new type of high efficiency grating coupler, based on single crystalline Si nanomembrane overlay and stacking. Such high efficiency diffractive grating couplers are designed for the purpose of coupling light between single mode fibres and nanophotonic waveguides, and for the coupling between multiple photonic interconnect layers for compact three-dimensional vertical integration. Two-dimensional model simulation based on eigenmode expansion shows a diffractive power-up efficiency of 81% and a fibre coupling efficiency of 64%. With nanomembrane stacking, it is feasible to integrate the side-distributed Bragg reflector and bottom reflector, which can lead to the diffractive power-up efficiency and the fibre coupling efficiency of 97% and 73.5%, respectively. For a negatively detuned coupler, the bottom reflector is not needed, and the diffractive power-up efficiency can reach 98% over a large spectral range. The device is extremely tolerant to fabrication errors.
TL;DR: Compared with current amplitude-type photomasks, switchable, phase-type fractal zone plates and fractal photon sieves demonstrated higher diffraction efficiency, an important factor in the future development of adaptive optics.
Abstract: Electrically switchable phase-type fractal zone plates and fractal photon sieves were fabricated using polymer-dispersed liquid crystal material based on a photomask. While both exhibited similar first-order diffraction behavior, the fractal photon sieves showed greatly suppressed diffraction at higher orders. Compared with current amplitude-type photomasks, our switchable, phase-type devices demonstrated higher diffraction efficiency, an important factor in the future development of adaptive optics.
TL;DR: A method to make optical mosaic gratings that uses the exposure beams and the latent grating created by the previous exposure to adjust the lateral position and readjust the attitude of the substrate for the current exposure is presented.
Abstract: We present a method to make optical mosaic gratings that uses the exposure beams and the latent grating created by the previous exposure to adjust the lateral position and readjust the attitude of the substrate for the current exposure. As thus, it is a direct method without using any auxiliary reference grating(s) and it avoids the asynchronous drifts between otherwise independent exposure and alignment optical sub-systems. In addition, the method uses a red laser wavelength in the plane-mirror interferometers for the multi-dimensional attitude adjustment, so the adjustment can be done at leisure. The mosaic procedure is described step by step, and the principles to minimize substrate alignment errors are explained in detail. Experimentally we made several mosaics of (50 + 30) x 50 mm(2) final grating area. The typical peak-valley and root-mean-square values of the measured -1st-order diffraction wavefront errors are 0.036 lambda and 0.006 lambda, respectively.
TL;DR: In this paper, a holographic polymer-dispersed liquid crystal (HPDLC) diffraction gratings were used for optical communications, diffractive optics and optical data storage, and the redistribution of LCs was observed by using phase contrast microscopy and confocal Raman spectroscopy.
Abstract: Polymer-dispersed liquid crystal (PDLC) is a material promising for application in optical communications, diffractive optics and optical data storage. Diffraction gratings were optically recorded in a novel PDLC material developed at the Centre for Industrial and Engineering Optics. Details of the fabrication and preliminary results of electro-optical switching of the holographic PDLC (HPDLC) diffraction gratings are presented. The redistribution of LCs was observed by using phase contrast microscopy and confocal Raman spectroscopy.
TL;DR: In this article, a phase volume reflection hologram is written in a photopolymer layer and is used as a screen for a signal beam, and the experimental realization of a head-up-display based on a polymeric material is presented.
Abstract: We present the experimental realization of a head-up-display based on a photopolymer. A phase volume reflection hologram is written in a photopolymer layer and is used as a screen for a signal beam. To write efficient holograms in the polymeric material we used ordinary and modified polymethylmethacrylate matrices containing phenanthrenequinone (PQ). Increasing the PQ concentration gives us an opportunity to realize thinner layers (<100 mum) saving high values of the diffraction efficiency. Decreasing the thickness of the layer allows higher observation angles of the received image and a wider spectral range of the incident light.
TL;DR: In this paper, a modulated femtosecond laser focused with cylindrical lenses was used to construct a volume grating with an area of 2.5mm × 3mm and ∼2mm thickness.
Abstract: We report on rapid fabrication of optical volume gratings in Foturan glass using a modulated femtosecond laser focused with cylindrical lenses. An optical volume grating with an area of 2 mm ×3 mm and ∼2 mm thickness can be achieved within 10 min by use of this method. Optical micrography confirms the volume nature of the gratings and shows that they consist of 10 μm-thickness planes with a period of 15 μm. The diffraction efficiency is examined to be ∼56%. The limitations and future implementations of the fabricated volume gratings are discussed.
TL;DR: The accuracy of the finite-element method is demonstrated to calculate the diffraction efficiencies of an arbitrarily shaped crossed grating in a multilayered stack illuminated by an arbitrarily polarized plane wave under oblique incidence.
Abstract: We demonstrate the accuracy of the finite-element method to calculate the diffraction efficiencies of an arbitrarily shaped crossed grating in a multilayered stack illuminated by an arbitrarily polarized plane wave under oblique incidence. The method has been validated by using classical cases found in the literature. Finally, to illustrate the independence of our method with respect to the shape of the diffractive object, we present the global energy balance resulting from the diffraction of a plane wave by a lossy thin torus crossed grating.
TL;DR: Large bandwidth, highly efficient, high dispersion dielectric gratings in reflection, transmission, and immersed transmission geometry, and a transmission grating in the classical scattering geometry is suggested, that features a buried high index layer.
Abstract: We analyze the diffraction characteristics of dielectric gratings that feature a high index grating layer, and devise, through rigorous numeri-cal calculations, large bandwidth, highly efficient, high dispersion dielectric gratings in reflection, transmission, and immersed transmission geometry. A dielectric TIR grating is suggested, whose −1dB spectral bandwidth is doubled as compared to its fused silica equivalent. The short wavelength diffraction efficiency is additionally improved by allowing for slanted lamella. The grating surpasses a blazed gold grating over the full octave. An immersed transmission grating is devised, whose −1dB bandwidth is tripled as compared to its fused silica equivalent, and that surpasses an equivalent classical transmission grating over nearly the full octave. A transmission grating in the classical scattering geometry is suggested, that features a buried high index layer. This grating provides effectively 100% diffraction efficiency at its design wavelegth, and surpasses an equivalent fused silica grating over the full octave.
TL;DR: The authors find healing to be accelerated in dye doped polymers and this "healing" process is studied and quantified using Nomarski Differential Interference Contrast optical microscopy and diffraction efficiency measurements of micro-machined gratings.
Abstract: Femtosecond lasers have a unique ability of processing bulk transparent materials for various applications such as micromachining, waveguide manufacturing, and photonic bandgap structures, just to name a few. These applications depend on the formation of micron or submicron size features are known to be index modifications to the bulk substrate [2, 11], which were thought to persist indefinitely. However, it has been observed that some of these bulk transparent materials recover or "heal" with time. This "healing" process is studied and quantified using Nomarski Differential Interference Contrast optical microscopy and diffraction efficiency measurements of micro-machined gratings. We find healing to be accelerated in dye doped polymers.
TL;DR: Improved cavity-finesse methods for characterizing the diffraction efficiencies of large gratings at the Littrow angle prove that a high diffraction efficiency with low variation is achievable across large apertures for gratings.
Abstract: We have developed improved cavity-finesse methods for characterizing the diffraction efficiencies of large gratings at the Littrow angle. These methods include measuring cavity length with optical techniques, using a Michelson interferometer to calibrate piezoelectric transducer nonlinearities and angle-tuning procedures to confirm optimal alignment. We used these methods to characterize two 20 cm scale dielectric gratings. The values taken from across their surfaces collectively had means and standard deviations of μ=99.293% and σ=0.164% and μ=99.084% and σ=0.079%. The greatest efficiency observed at a single point on a grating was (99.577+/-0.002)%, which is also the most accurate measurement of the diffraction efficiency in the literature of which we are aware. These results prove that a high diffraction efficiency with low variation is achievable across large apertures for gratings. © 2009 Optical Society of America