Design, optical characterization, and operation of large transmission gratings for the laser integration line and laser megajoule facilities

Within the framework of the laser integration line (LIL) and the laser megajoule, we describe the design, optical characterization, mounting, alignment, and operation on the LIL of large 420 mm x 470 mm transmission gratings. Two types of grating were manufactured. The first, operating at a wavelength of 1.053 microm, was used for deviation purposes. The second, operating at a wavelength of 0.351 microm, was used for both deviation and focusing purposes. We demonstrate that these large transmission gratings are suitable for nanosecond-regime operation on high-power laser facilities.     

Design and characterization of a microchannel optical interconnect for optical backplanes

The design, modeling, and experimental characterization of a microchannel-based free-space optical interconnect is described. The microchannel interconnect was used to implement a representative portion of an optical backplane that was based on field-effect transistor, self-electro-optic device smart-pixel transceivers. Telecentric relays were used to form the optical interconnect, and two modes based on two different optical window clusterings were implemented. The optical system design, including the optical geometry for different degrees of clustering of windows supported by a lenslet relay and the image mapping associated with a free-space optical system, is described. A comparison of the optical beam properties at the device planes, including the spot size and power uniformity of the spot array, as well as the effects of clipping and misalignment for the different operating modes, is presented. In addition, the effects of beam clipping and misalignment for the different operating modes is presented. We show that microchannel free-space optical interconnects based on a window-clustering scheme significantly increase the connection density. A connection density of 2222 connections/cm(2) was achieved for this prototype system with 2 x 2 window clustering.     

Activation analysis and first occupational dose rates estimates for the Laser Megajoule facility

A three-dimensional neutronic modelling of the LMJ facility has been performed. The Monte Carlo transport code TRIPOLI is used to obtain the neutron spectra required for the inventory code FISPACT. Nodal activation responses and time-dependent decay gamma spectra are produced and used as source terms for further treatment by TRIPOLI for a range of engineering and safety assessments. It is shown that three-dimensional neutronic and nodal activation can be performed in a convenient way and the results obtained by this procedure will serve as a data-base for design and S&E analysis.     

Laser ablative shaping of plastic optical components for phase control

A new scheme for phase control of optical components with laser ablation has been developed. One can ablate the surface shape of optical plastic material coated on a glass plate by using 193-nm laser light to control the transmission wave front. The surface shape is monitored in situ and corrected to attain the desired aberration level. The irradiation fluence is approximately 40 mJ/cm(2), and the ablation depth/pulse is approximately 0.01 mum/pulse for UV-cured resin. A wave-front aberration of 3.0 lambda is reduced to 0.17 lambda for flat surface shaping. For spherical surface generation, an aberration of 2.5 lambda is reduced to 0.2 lambda. The increase in surface roughness is kept within acceptable levels.     

Production and characterization of spiral phase plates for optical wavelengths

We describe the fabrication and characterization of a high-quality spiral phase plate as a device to generate optical vortices of low (3-5) specified charge at visible wavelengths. The manufacturing process is based on a molding technique and allows for the production of high-precision, smooth spiral phase plates as well as for their replication. An attractive feature of this process is that it permits the fabrication of nominally identical spiral phase plates made from different materials and thus yielding different vortex charges. When such a plate is inserted in the waist of a fundamental Gaussian beam, the resultant far-field intensity profile shows a rich vortex structure, in excellent agreement with diffraction calculations based on ideal spiral phase plates. Using a simple optical test, we show that the reproducibility of the manufacturing process is excellent.     

Design and fabrication of a freeform phase plate for high-order ocular aberration correction

In recent years it has become possible to measure and in some instances to correct the high-order aberrations of human eyes. We have investigated the correction of wavefront error of human eyes by using phase plates designed to compensate for that error. The wavefront aberrations of the four eyes of two subjects were experimentally determined, and compensating phase plates were machined with an ultraprecision diamond-turning machine equipped with four independent axes. A slow-tool servo freeform trajectory was developed for the machine tool path. The machined phase-correction plates were measured and compared with the original design values to validate the process. The position of the phase-plate relative to the pupil is discussed. The practical utility of this mode of aberration correction was investigated with visual acuity testing. The results are consistent with the potential benefit of aberration correction but also underscore the critical positioning requirements of this mode of aberration correction. This process is described in detail from optical measurements, through machining process design and development, to final results.     

Precise measurement of optical phase retardation of a wave plate using modulated-polarized light

We propose a new method for precisely measuring the optical phase retardation of a wave plate using modulated-polarized light. Modulated-polarized light is used such that the zeros of the system can be accurately determined. A Babinet-Soleil compensator is employed to measure the optical phase retardation. A cross-wavelength measurement is also proposed for determining the phase retardation at a wavelength, which is not the measuring wavelength.     

Design, implementation, and characterization of a hybrid optical interconnect for a four-stage free-space optical backplane demonstrator

A four-stage unidirectional ring free-space optical interconnect system was designed, analyzed, implemented, and characterized. The optical system was used within a complementary metal-oxide semiconductor-self-electro-optic-effect-device-based optical backplane demonstrator that was designed to fit into a standard VME chassis. This optical interconnect was a hybrid microlens-macrolens system, in which the microlens relays were arranged in a maximum lens-to-waist configuration to route the optical beams from the optical power supply to the transceiver arrays, while the macrolens optical relays were arranged in a telecentric configuration to route optical signal beams from stage to stage. The following aspects of the optical system design are discussed: the optical parameters for the hybrid optical system, the image mapping of the two-dimensional array of optical beams from stage to stage, the alignment tolerance of the hybrid relay system, and the power budget of the overall optical interconnect. The implementation of the optical system, including the characterization of optical components, subsystem prealignment, and final system assembly, is presented. The two-dimensional array of beams for the stage-to-stage interconnect was adjusted with a rotational error of <0.05 degrees and a lateral offset error of <3.5 mum. The measured throughput is in good agreement with the lower-bound predictions obtained in the theoretical results, with an optical power throughput of -20.2 dB from the fiber input of the optical power supply to the modulator array and -25.5 dB from the fiber input to the detector plane.     

Boundary layer above a semi-infinitely large hot plate in a medium with phase transition

A self-adjoint solution in the boundary layer approximation is constructed to the problem of streamlining of a hot plate by a medium in which a phase transformation occurs. A longitudinal pressure gradient exists within the region of the liquid phase.Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 38, No. 6, pp. 1044–1048, June, 1980.     

Design, fabrication, and evaluation of a multilevel spiral-phase Fresnel zone plate for optical trapping

A compact optics configuration for the generation of donut beams for trapping atoms at the micrometer scale using a multilevel spiral-phase Fresnel zone plate (FZP) and a semiconductor laser is proposed. A FZP is designed and a multilevel spiral phase is integrated into it. A spiral-phase FZP with a radius of 1?mm and with more than 1300 half-period zones is designed with multiple angular levels for integer and fractional topological charges, and the device is fabricated using electron-beam lithography direct writing. The performance of the device is evaluated, and the generation of symmetric and asymmetric donut beams is successfully demonstrated.     

Design and characterization of a liquid-crystal spatial light modulator for a polarization-insensitive optical space switch

We report preliminary results concerning a free-space optical switch between single-mode fibers with a ferroelectric liquid-crystal (FLC) spatial light modulator (SLM). In particular, we show experimentally that such a device can operate in a polarization-insensitive manner. The influence of the geometrical and physical features of the FLC SLM on the overall performance of the optical fiber switch are also discussed.     

Mode purity comparison of optical vortices generated by a segmented deformable mirror and a static multilevel phase plate

We present a mode purity comparison between optical vortices (OVs) generated by a static multilevel phase plate with 16 or 32 phase steps and a vortex generated with a segmented deformable mirror with 37 actuators. Computer simulations show the intensity and phase of the vortices generated with the two methods. The deformable mirror, by being reconfigurable, shows better mode purity for high charge OVs, while the static phase plate mode efficiency declines due to the fixed number phase quantization.     

Design, implementation, and characterization of an optical power supply spot-array generator for a four-stage free-space optical backplane

The design and implementation of a robust, scalable, and modular optical power supply spot-array generator for a modulator-based free-space optical backplane demonstrator is presented. Four arrays of 8 x 4 spots with 6.47-mum radii (at 1/e(2) points) pitched at 125 mum in the vertical direction and 250 mum in the horizontal were required to provide the light for the optical interconnect. Tight system tolerances demanded careful optical design, robust optomechanics, and effective alignment techniques. Issues such as spot-array generation, polarization, power efficiency, and power uniformity are discussed. Characterization results are presented.     

High-power efficient multiple optical vortices in a single beam generated by a kinoform-type spiral phase plate

We propose using a solitary kinoform-type spiral phase plate structure to generate an array of vortices located in a single beam. Kinoform-type spiral surfaces allow each wavelength component of the phase modulation value to be wrapped back to its 2 pi equivalent for optical vortices of high charge. This allows the surface-relief profiles of high-charge vortices to be microfabricated with the same physical height as spiral phase plates of unity-charged optical vortices. The m-charged optical vortex obtained interacts with the inherent coherent background, which changes the propagation dynamics of the optical vortex and splits the initial m charge into /m/ unity-charged optical vortices within the same beam. Compared to a hologram, a multistart spiral phase plate is more efficient in the use of available spatial frequencies and beam energy and also is computationally less demanding. Furthermore, using microfabrication techniques will allow for greater achievable tolerances in terms of smaller feature sizes.     

Design, implementation, and characterization of a folded spot-array generator for a modulator-based free-space optical interconnect

A folded structured light generator is presented. This spot generator is to be used in a modulator-based free-space optical interconnect. Three cascaded diffractive optical elements produce 4 x 8 clusters on an 800 microm x 1600 microm pitch, in which each cluster is a 4 x 4 array of 13.1-microm-radius spots on a 90-microm pitch. The folded configuration is more compact than an existing linear spot-array generator and replaces 14 optical surfaces with eight surfaces. Details of the optical design, sensitivity analysis, alignment techniques, assembly, and test results are presented.     

Random phase plate for wavefront sensing via phase retrieval and a volume speckle field

A random phase plate is prepared by illuminating a photoresist plate with a fully developed speckle field and using the developed phase plate (DPP) as a diffuser. Wavefront sensing is implemented using phase retrieval based on the recording of speckle intensity patterns at various distances from the DPP and the wave propagation equation. The effects of the roughness height of the DPP on the phase retrieval are investigated. From simulations a roughness height of lambda/10 results in a speckle field that yields good phase reconstruction for the spherical test wavefront incident on the DPP. From the experiments different portions of the DPP that received varying exposures are examined. A section of the phase plate with a characteristic roughness height facilitated the generation of a speckle field that is optimum for the phase retrieval algorithm. Thus a random phase plate with varying roughness height allows optimized measurements of wavefronts with different curvatures. Analytical expressions describing the second-order intensity statistics (fourth-order field statistics) for a field traversing a specific diffuser are presented. This DPP will not give rise to a fully developed speckle field, but knowing the statistics of the depth of the DPP will facilitate a rigorous treatment of the problem.     

Laser methods and facilities for monitoring the geometric dimensions of components

Comparative characteristics are provided for laser methods of measuring geometric dimensions of components. The main problems are considered that arise with measurement by the triangulation method. An instrument is described that makes it possible to measure the parameters of railway wagon spring suspenders. __________ Translated from Izmeritel’naya Tekhnika, No. 2. pp. 32–35, February, 2008.     

Design and characterization of a femtosecond fluorescence spectrometer based on optical Kerr gating

Design and characterization of a general-purpose spectrometer for recording time-resolved emission spectra of typical fluorescent species is described. The system is based on a high repetition rate amplified Ti : sapphire system, an optical Kerr shutter for gating the emission, and a polychromator plus charge-coupled device (CCD) detection system. Using 1 mm of liquid benzene as the Kerr medium, and optics designed to provide high polarization quality, emission spectra of dilute solutions of solutes with nanosecond lifetimes can be recorded with good signal-to-noise ratios. The current spectrometer uses excitation wavelengths near 390 nm and provides spectra over the wavelength range 400-650 nm with 4 nm resolution and instrument response times of 450 fs (full width at half-maximum, FWHM). Selected applications are described to demonstrate the utility of this instrument.     

Optimization of a silicon X-ray phase plate

We report that X-ray phase plates give optimal performance when operated, not at the exact Bragg angle but at the angle for which the phase shift is reduced by π. This operating point maximizes the output of circular polarization by accepting larger beam divergence.     

Laboratory facilities and recommendations for the characterization of biological ultraviolet dosimeters

A laboratory facility for characterizing biological dosimeters for the measurement of UV radiation has been built and tested. The facility is based on a solar simulator, stabilized by photofeedback, and monitored by a spectroradiometer, with a versatile filter arrangement. This enables the following characteristics of the dosimeters to be ascertained: spectral response, linearity, and reciprocity; angular acceptance and response; calibration in simulated sunlight. The system has been tested on a variety of dosimeters and has the potential to be used with other radiometers, subject currently to the size of their active surface.