Measurement of three-dimensional temperature fields with interferometric tomography

Optical computerized tomography (OCT) technology is used to reconstruct the asymmetric three-dimensional temperature field generated by radiators and electronic chips. First, the OCT method is described. Second, the reconstructed results are tested by a double-cylinder radiator model. Finally, OCT is applied to reconstruction of the temperature field above the surface of a CPU. The air-temperature field above a CPU circuit can be imaged with an OCT system that reflects whether the heat production from different parts of the CPU is even; therefore possibly the technique can be used to determine whether the integrated-circuit design in the CPU is smart.     

Optical design of the wide angle camera for the Rosetta mission

The final optical design of the Wide Angle Camera for the Rosetta mission to the P/Wirtanen comet is described. This camera is an F/5.6 telescope with a rather large 12 degrees x 12 degrees field of view. To satisfy the scientific requirements for spatial resolution, contrast capability, and spectral coverage, a two-mirror, off-axis, and unobstructed optical design, believed to be novel, has been adopted. This configuration has been simulated with a ray-tracing code, showing that theoretically more than 80% of the collimated beam energy falls within a single pixel (20" x 20") over the whole camera field of view and that the possible contrast ratio is smaller than 1/1000. Moreover, this novel optical design is rather simple from a mechanical point of view and is compact and relatively easy to align. All these characteristics make this type of camera rather flexible and also suitable for other space missions with similar performance requirements.     

Optical interferometry with pulsed fields

The problem of predicting and interpreting the results of interferometric optical experiments involving pulse trains is addressed. Specifically, a cyclostationary field arising from the modulation of a stationary, stochastic source is considered in the classical Young's experiment. It is shown that the effects of modulation may be identical to unrelated statistical interference effects.     

Corrections and uncertainties for neutron fluence measurements with proton recoil telescopes in anisotropic fields

By means of a Monte Carlo simulation correction factors and uncertainties in neutron fluence determination with a proton recoil telescope were deduced in the energy range of MeV ≤ E_n ≤ 14 MeV. The calculation took into account the properties of the deuteron beam, the deuterium gas target and the telescope. The influence of in- and out-scattering of neutrons and recoil protons was considered. Analysis of the experiments showed that an uncertainty of 2.0% (standard deviation) in neutron fluence determination can be obtained. A detailed listing of uncertainties is given which allows a covariance matrix to be generated.     

Loss-induced phase-sensitive spatial light modulator with a wide field of view

We investigate the feasibility of achieving practical phase modulation by changing only the absorption of the device. We present a spatial light modulator that consists of a three-mirror cavity with lossy slabs inserted between the mirrors. When only the absorption of these slabs is changed, this device can have a gradual change in phase, but no intensity modulation. Theoretical analysis by the use of numbers appropriate to multiple quantum wells shows that the total phase-tuning range can be as large as 2π with an absorption coefficient change of less than 9000 cm(-1); the length of each multiple-quantum-well slab is ~ 1.5 μm. This gives an expected 16° field of view with the nanosecond speed typical of semiconductors.     

Optical analysis of spherical mirrors of telescopes: The lens-less Schmidt case

The light distribution on the focal surface of spheric mirrors designed for telescopes in the lens-less Schmidt configuration is calculated analytically using geometrical optics.This analysis was motivated by considerations of the design of the AUGER fluorescence detector [J. Abraham, et al., Nucl. Instr. and Meth. A 533 (2004) 50]. Its geometrical parameters are used in the examples.     

Computational and interferometric system for real-time limited-view tomography of flow fields

A modified iterative conjugate gradient technique is developed and applied to limited-view interferometric tomography for reconstructing flow fields of simple structure. The approach is also effective in dealing with significant noise present in the data. From a computer simulation of experiments, a multipath interferometric system is built, from which multidirectional projection interferograms can be captured in real time for fast transient phenomena. The system is employed to measure an asymmetric temperature field. The three-dimensional field is then reconstructed with the developed experimental and computational techniques. The results are satisfactory when compared with thermocouple measurements.     

望远镜中扰动抑制的Youla控制器优化设计

在微弧度级的大型望远镜中,抑制振动已经成为一项非常关键的技术。在微弧度级的大型望远镜中,抑制振动已经成为一项非常关键的技术。经典的反馈控制方法由于图像传感器本身具有采样频率低、积分时间长的特点使得控制回路的带宽受限的原因不能很好地抑制回路中的扰动,尤其是存在范围广、能量较大的宽带扰动。本文基于优化的力设计理念提出一种扰动抑制的Youla控制器优化设计方法来提高系统的宽带扰动抑制能力。在可以获取到宽带扰动频率的情况下,该方法通过设计合适的Q滤波器去适应宽带扰动,从而达到抑制扰动的目的。仿真及实验结果表明,相对于传统的比例-积分控制方法,该方法极大地提高了系统的宽带扰动抑制能力,增强了系统的闭环性能。此外,由于此方法模型依赖程度低、易于实现,故可以推广到许多工程实际中。     

Optical currents in vector fields

We present the results of computer simulation of the spatial distribution of the Poynting vector and illustrate motion of microparticles and nanoparticles in spatially inhomogeneously polarized fields. The influence of phase relations and the degree of mutual coherence of superimposing waves on the characteristics of the microparticle's motion has been analyzed. For the first time, we have shown experimentally the possibility of diagnostics of optical currents in liquids caused by polarization characteristics of an optical field alone, using test metallic particles of nanoscale.     

Optical design with parametrically defined aspheric surfaces

The standard aspheric surface definition has been used successfully to correct aberrations in a wide variety of systems. However, in some current applications a more general surface definition is needed. We present a more general approach that uses parametrically defined optical surfaces for the optical design of imaging and illumination systems.     

Design of a compact off-axis two-mirror freeform infrared imager with a wide field of view

With the development of modern precision optical fabrication and measurement technologies, optical freeform surfaces have been widely employed in different applications, especially in off-axis reflective optical systems. For an infrared optical system operating in the long-wavelength spectrum, compactness, brightness, and a wide field of view are key requirements for military surveillance or scene sensing. In this paper, we present an off-axis two-mirror freeform infrared imager with compactness and brightness. It has a large pupil of size 12?mm and a fast focal ratio of 2.2 over a wide 23° diagonal field of view, as well as good image quality. XY-polynomial freeform surfaces are applied to the viewing mirror and focusing mirror. The multiple degrees of freedom of optical freeform surfaces are very helpful for off-axis aberration correction and improving the optical performance over the entire pupil across the full field of view. The overall dimension of our designed freeform infrared imager is about 30?mm by 30?mm by 30?mm, which is elegantly miniaturized. The final designed results of a reflective freeform infrared imager are demonstrated and discussed in detail.     

Bare-eye view at the nanoscale: new visual interferometric multi-indicator (VIMI)

By exploiting the interferometric antireflection action of a probe sample, consisting of a diamond-like carbon (DLC) film grown on Si, combined with a specific illumination spectrum, we designed and constructed an optical device for the visual remote sensing of radiation (either plasma or atomic oxygen) and for the visual inspection of adsorbed organic contamination as thin as a few molecular layers. The capabilities of this new visual interferometric multi-indicator (VIMI) enable the bare-eye color detection of thickness changes on the order of a few nanometers without the intervention of any instrumental or computer interface.     

Optical phase contrast measurement of ultrasonic fields

This report describes an optical phase contrast imaging technique for the measurement of wide bandwidth ultrasound fields in water. In this method, a collimated optical wavefront (λ_l = 810 nm) impinges on a wide bandwidth ultrasound pulse. The method requires that refractive index perturbations induced by the ultrasound field be sufficiently small. Specifically, on exit from the acoustic field, the phase of the optical wavefront must be proportional to the ray sum of local density taken in the direction of propagation of the incident optical wave. A similar restriction is placed on the dimensions of the ultrasound pulse. Repeated measurement of this phase as the ultrasound field is rotated through 180° about an axis normal to the direction of propagation of the incident optical wave generates the Radon transform of the ultrasonically induced refractive index perturbation. Standard tomographic reconstruction techniques are used to reconstruct the full three-dimensional refractive index perturbation. A simple two-lens imaging system and an optical signal processing element from phase contrast microscopy provide a method of directly measuring an affine function of the desired optical phase for small optical phase shifts. The piezo- and elasto-optic coefficients (the first partial derivatives of refractive index with respect to density and pressure) relate refractive index to density and pressure via a linear model. The optical measurement method described in this paper provides a direct, quantitative measurement of the piezo- and elasto-optic coefficients (from the density or pressure fields)     

高分辨率大视场线扫描共焦显微镜的设计与研制

商用共聚焦显微镜使用二维光点扫描对样品成像,成像帧频被限制在30 Hz以内,扫描速度大多在10帧/秒(f/s)左右。为了提高共聚焦系统成像速度,满足生物细胞在体成像的需求,本文使用线光束对样品进行一维扫描照明,成像速度大大提高,同时根据共聚焦成像原理,在线阵CCD前使用狭缝滤除非聚焦平面杂散光以提高成像质量。实验表明,系统光学放大倍率为55倍,横向分辨率高于2.2 μm,当线阵CCD以28 kHz行频扫描成像时,帧频可达50 f/s,通过对动植物细胞成像证明,本系统可用于生物细胞的在体成像。     

Optical trapping of dielectric particles in arbitrary fields

We present a new method to calculate trapping forces of dielectric particles with diameters D < or = lambda in arbitrary electromagnetic, time-invariant fields. The two components of the optical force, the gradient force and the scattering force, are determined separately. Both the arbitrary incident field and the scatterer are represented by plane-wave spectra. The scattering force is determined by means of the momentum transfer in either single- or double-scattering processes. Therefore the second-order Born series is evaluated and solved in the frequency domain by Ewald constructions. Numerical results of our two-force-component approach and an established calculation method are compared and show satisfying agreement. Our procedure is applied to investigate axial trapping by focused waves experiencing effects of aperture illumination and refractive-index mismatch.     

Fundamental and exotic physics with Cherenkov telescopes

The detection of high-energy γ rays from astrophysical sources, using the Fermi/LAT detector and in the very-high-energy limit the Cherenkov telescopes MAGIC, H.E.S.S. and VERITAS, can provide tests of fundamental physics with unprecedented sensitivity, and possibly allows to probe new and exotic scenarios.