Transmissive Elements Research Articles

Parametric dependencies of high-diffraction-order achromatized aplanatic configurations that employ circular or crossed-linear diffractive optical elements.

The parametric relationships of achromatized transmissive and reflective diffractive optical elements (DOEs) are explored for a number of configuration classes as a function of diffraction order, focal ratio, wavelength, and field angle. The necessity for blazing high-diffraction-order DOEs is elucidated. The ray image sizes are presented in dimensionless imaging space and thus are applicable to any size of optical system. Several aplanatic configurations are evaluated.

Thermal embossing of mid-infrared diffractive optical elements by use of a self-processing photopolymer master

Surface-relief transmissive diffractive elements were fabricated by embossing. The master was made by lithography with a self-developing photopolymer. The highly cross-linked structure exhibited by the polymer has made possible the direct replication by thermal embossing of polyethylene substrates. Fabricated elements are meant to work with mid-infrared radiation. The influence of some process variables, related to the performance of the diffractive elements, is analyzed.

Diffractive optical elements for intra-cavity beam-shaping of laser modes

Diffractive optical elements (DOE) are applied as intra-cavity mode selection devices for customizing the fundamental mode of laser resonators for high power laser systems. Using a phase-conjugating mode selecting element (MSE) in a laser oscillator, we are able to produce a good approximation to a super-Gaussian mode with a near flat intensity profile. This offers higher energy extraction from any following laser amplifiers compared to an unmodified Gaussian TEM00 mode. Two different designs for operation in a 1 m cavity length Nd:YAG master oscillator are presented. Both designs are surface relief phase elements fabricated in fused silica using photolithography with reactive-ion etching to produce 16 level elements for use in transmission. One element is designed to replace the cavity end mirror, while the other stands off an arbitrary distance from the end mirror. A novel iterated design for these transmissive elements is introduced. Numerical results and experimental measurements are presented and discussed.

11.1: Invited Paper: Switchable Reflective Displays Formed from Holographic Polymer‐Dispersed Liquid Crystals (H‐PDLCs)

AbstractHolographically formed polymer dispersed liquid crystals (H‐PDLC) films show excellent promise in the development of switchable transmissive and reflective diffractive optical elements. The use of holographic photopolymerization allows for the development of spatially periodic gratings of nano‐scale sized LC domains. Reflection gratings exhibiting blue, green or red colors can be routinely fabricated and electrical switching has been demonstrated. Reflective H‐PDLCs have been investigated in terms of their electro‐optical performance parameters and their potential as a viable display system. These films exhibit low switching fields, high contrast ratios, high transmission in the on and off states and fast switching speeds on the order of microseconds. The state of the art performance levels and existing challenges in this new technology are broadly discussed.

Theory and laboratory demonstrations on the use of a nematic liquid-crystal phase modulator for controlled turbulence generation and adaptive optics

We discuss the use of liquid-crystal phase modulators (LCPM's) both as a repeatable disturbance test source and as an adaptive optics corrector. LCPM's have the potential to induce controlled, repeatable, dynamic aberrations into optical systems at low cost, low complexity, and high flexibility. Because they are programmable and can be operated as transmissive elements, they can easily be inserted into the optical path of an adaptive optics system and used to generate a disturbance test source. When used as wave-front correctors they act as a piston-only segmented mirror and have a number of advantages. These include low operating power requirements, relatively low cost, and compact size. Laboratory experiments with a Meadowlark LCPM are presented. We first describe use of the LCPM as a repeatable disturbance generator for testing adaptive optics systems. We then describe a closed-loop adaptive optics system using the LCPM as the wave-front corrector. The adaptive optics system includes a Shack-Hartmann wave-front sensor operated with a zonal control algorithm.

Simple high-precision method for measuring the specular reflectance of optical components

We present a simple method to determine precisely the specular reflectance of optical components. The absence of transmissive elements in this method makes a wide spectral range available. High accuracy and precision are achieved with a fast, periodic change between the reference beam and the probe beam. Special efforts were made to eliminate inhomogeneities of beam intensity and detector sensitivity. With our experimental setup we obtain a precision of ±3 × 10(-4) at the wavelength of 10.6 µm and ±3 × 10(-5) at 1.06 µm for a single-bounce-measuring setup.

Gel-silica optics: Theory and application

A new generation of silica optics has resulted from alkoxide-based sol-gel processing of silica including: net shape transmissive optical elements, surface diffractive optics, inorganic doped GRIN optics, organic impregnated optical composites such as dye lasers and scintillators, optics with internal diffraction gratings, laser densified microoptical lenses and arrays, and laser densified waveguides. Processing control of the ultrastructure of the monolith at the time of gelation and during aging is essential to producing the optical devices together with chemical and thermal stabilization of the surface of the pore network prior to densification or impregnation. The process control variables for gel-silica optics are summarized together with spectroscopic analysis and molecular orbital calculations that explain how and why the thermal-chemical processing controls work at a molecular level.

Thermally Activated Transmissive Optical Elements for Rejection of Laser Radiation

AbstractThe sacrificial thermal shutter/reflector concept is suitable for optical power limiting in optical systems containing an intermediate focus and uses a thermally activated chemical process to form a mirror that reflects a large fraction of the incident laser light. Under normal illumination, the thermal reflector component is a transmissive optical element at or near a focal plane of an optical system. A pulse from an incident laser beam heats a film of precursor chemicals on the optical element and thereby converts it to a localized reflective metallic mirror. For visible laser pulses longer than 0.1 ms, the thermal shutter provides optical limiting at energies below the ANSI Maximum Permissible Exposure (MPE) standard for laser eye protection. For shorter pulses, near-MPE limiting is achieved. See-through during exposure is also possible with these elements. Various thermal shutter chemistries and efforts to form optically clear thin precursor films are described. The laser testing results highlight the importance of the substrate and absorber in these devices.

Aspheric holographic elements for far IR radiation

A novel method for designing and recording aspheric computer generated holographic optical elements for far infrared radiation has been developed. The design method is based on analytic ray-tracing procedure that exploits the minimization of the mean-squared difference of the propagation vectors between the actual output wavefronts and the desired output wavefronts. This minimization yields a solution for the aspheric grating vector. The design method is illustrated by recording and testing aspheric reflective and transmissive off-axis focussing elements for 10.6 μm wavelength having diffraction-limited performance over a broad range of incidence angles.

Efficient multilevel phase holograms for CO_2 lasers

Multilevel phase holograms for monochromatic radiation at a wavelength of 10.6 microm are recorded as surface relief gratings with multilevel discrete binary steps. Our experiments show that diffraction efficiencies close to 90% can be achieved both for transmissive and reflective elements. The reduction of efficiency due to errors in the depth and the width of the step levels is considered.

Fabrication and Evaluation of Transmissive Multilayer Optics for 8keVX Rays

ABSTRACTWe have made and tested several sliced multilayer structures which can function as transmissive x-ray optical elements (diffraction gratings, zone plates, and phase gratings) at 8 keV. Our automated multilayer sputtering system is optimized to sputter layers of arbitrary thickness for very large total deposits at high deposition rates. Diffraction patterns produced by the multilayer devices closely match theoretical predictions. Such transmissive optics have the potential for wide application in high resolution microscope and spectrometer systems.