The analysis and design of multiple phase plane for wave front coding system

With the rapid developing of science and technology, large aperture optical system plays an important role in the hightech fields including space optics, astronomical optics, inertial confinement fusion, the detecting and recognizing of space target. However, the problems of the wavefront sensing about large aperture optical system has been totally solved because of the equipment expenses and long manufacturing periods. In order to test the large aperture elements in optical system with cheaper costs and higher resolution, more and more attentions are paid into the wavefront sensing of large aperture optical systems. The scanning pentaprism system is introduced to divide the wavefront of the interferometer into a series of sub-wavefront, and the relative positions of the spot centroid accroding to every sub-wavefront are recorded on the CCD camera. The normal directions of every sub-wavefront are obtained to reconstruct the tested wavefront. Experimental results are accord with the interferometer measure results. The feasibility of the pentaprism scanning method has been validated. Finally the influences of measurement apparatus and environment on the measuring precision is discussed. Which is useful to expand the measuring range to keep high spatial resolution and reduce cost.

The general principles of designing wide angle, large aperture optical systems are addressed. In particular, the advantages and disadvantages of reflective and refractive optical systems are discussed. It is shown that reflective optics have an inherently smaller field of view than do refractive systems. Conservation of etendue is discussed and directly applied to the determination of focal plane size of all optical systems as well as the central obscuration of systems with reflective primaries.

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The pulse-echo technique has been widely used in medical ultrasound imaging. This technique uses an array of transducer elements to transmit a focused beam into the body, and each element then becomes a receiver to collect the echoes. The received echoes from each element are dynamically focused to form an image. Focusing on transmission and reception is performed assuming that the wave propagation speed inside the body is the same everywhere. Unfortunately, the speed inside the body is not constant; it varies from 1470 m/s to greater than 1600 m/s. This speed variation will result in increased side lobes and degraded lateral resolution. Aberration phenomena and their extent in tissue have been evaluated in many works (O'Donnell & Flax 1988; Zhu & Steinberg, 1992; Shmulewitz et al., 1993; Robinson et al., 1994; Hinkelman et al., 1998). The degradation might be tolerable if the frequency is not very high and the aperture size of the array is not very large. However, higher frequencies and larger apertures have been used to improve lateral resolution of ultrasound images. But the resolution improvement cannot be achieved beyond a certain limit, because both larger aperture and higher frequency make the system more sensitive to propagation velocity variations in the body. For example, the four transverse abdominal scan images shown in the first row of Fig.1 were formed with a 64-element linear array using four different aperture sizes (9 mm, 12 mm, 18 mm, and 27 mm) to form each single beam in the image. The array pitch was 1.0 mm and the pulse had a 3.5 MHz centre frequency and 2 MHz bandwidth. The Superior-Mesenteric-Artery (SMA) and the Aorta (A) are the main objects in these images. Because of the shape of the rectus muscles (speed ~ 1580 m/s) and the fat layers (speed ~ 1450 m/s) at this position, the distortions caused by phase aberration in these images can be easily seen. In the 9-mm aperture image, the superior-mesenteric-artery is almost doubled but the artery wall can still be recognized. When the aperture size becomes larger, the distortion becomes worse. Phase aberration is one of the most important factors that limit improvement to lateral resolution of ultrasound imaging systems. Successful correction of phase aberrations will make it possible to improve the lateral resolution of images. Phase aberration corrected images using the near-field-signal-redundancy algorithm (Li, 1997) are shown in the second row of Fig.1 and the lateral resolution is improved when the aperture size becomes larger. In this chapter, the near-field-signal-redundancy algorithm is described in details. But first, a review of some related methods developed for phase-aberration correction is given. The

We report on the performance of FLAMINGOS, the world's first fully cryogenic near-IR multi-object spectrometer. FLAMINGOS has a fast all refractive optical system, which can be used at telescopes slower than f/7.5. This makes FLAMINGOS a very efficient wide-field imager when used on fast small aperture telescopes and a high AW spectrometer using laser machined aperture masks for MOS spectroscopy. FLAMINGOS uses a 2048x2048 HgCdTe HAWAII-2 array by the Rockwell Science Center. The array is readout through 32 amplifiers, which results in low overheads for observations. We describe both the operating characteristics of the HAWAII-2 array and of the array controller and data acquisition system. FLAMINGOS has been in operation for about 1.5 years and is now in routine use on four telescopes: The Kitt Peak 4-m and 2.1-m, The 6.5-m MMT and the 8-m Gemini South Telescope. We will describe the operating characteristics of FLAMINGOS on each of these telescopes that deliver fields-of-view from 21x21 arcminutes to 2.7x2.7 arcminutes and pixels from 0.6 arcseconds to 0.08 arcseconds. While providing a large AW product for fast telescopes (i.e. f/8), FLAMINGOS becomes progressively less efficient on slower telescopes. Since nearly all large telescopes have fairly slow optical systems (f/12 or slower) the combination of large aperture and slow optical systems makes FLAMINGOS ill suited for optimal performance on current large aperture telescopes. Thus, we are beginning construction of FLAMINGOS-2, which will be optimized for performance on the f/16 Gemini South 8-m telescope. Similar to FLAMINGOS, FLAMINGOS-2 will be fully refractive using grisms, laser machined aperture masks and a 2048x2048 HgCdTe HAWAII-2 array. FLAMINGOS-2 will provide a 6.1 arcminute field-of-view with 0.18 arcsecond pixels. FLAMINGOS-2 will also be designed to except an f/32 beam from the Gemini South MCAO system.

This paper gives a brief introduction to the spectrum of the solar light radiation characteristic. According to the aberration characteristics of the wide spectrum and large aperture optical system, two aberrations which are spherical aberration and chromatic aberration are corrected, transmission and reflection type solar light collection optical system are designed respectively. The optical system’s work waveband is 0.4~0.82μm, aperture is 600mm, focal length is 1320mm. The figures of optical system, spot diagram are given and the advantages and disadvantages of two systems which are transmission type and reflection type are compared.

We recently found that the intensity of the electric near field of a triangular aperture in a metal film is strongly localized at one edge of the aperture for incident light polarized perpendicular to this edge. Previous numerical calculations of the near field of a triangular aperture in a planar metal film, using the field susceptibility technique, yielded a nearly quantitative agreement with the experiments. Using this numerical technique, we have investigated the influence of an obliquely incident plane wave on the near field of small circular and triangular apertures. An interpretation of the numerical results leads to a deeper understanding of the way in which light transmission through the aperture is excited. The data suggest that after excitation of currents in the metal film by the incident light, a scattering of these currents by the aperture generates the near field of the aperture. We found that the excitation of small apertures (size <100 nm) is due to a tangential magnetic field whereas the perpendicular electric field plays no role. The excitation of a small aperture can thus be described exclusively by a magnetic polarizability. We found that for thin metal films an interference of the scattered field with the field transmitted through the metal film changes the near field pattern.

When testing the surface figure of large aperture optical components, phase noise of light source used in the phase shifting interferometer will influence the test precision. However, it is not easy to analyze the random phase noise directly. In order to have an understanding of phase noise, an experiment is designed to get beat frequency from two separate lasers. The possibility of obtaining phase noise from beat frequency is discussed. It is a good foundation for the improvement of the large aperture optical test system.

Background: The effects of acute pulmonary embolism (PE) on right ventricular (RV) diastolic function may be one of the determinants of right heart failure. We analysed the parameters of RV diastolic function in a porcine model of PE by the use of phase plane (PP) analysis. In the PP method, a periodic function is plotted such that the function, RV pressure (P), is the abscissa and its time derivative (dP/dt) is the ordinate. Methods: In six anaesthetised open chest pigs, RV pressure-volume (PV) loops were obtained by the conductance catheter technique. Measurements were realised in basal conditions, and repeated 1 hour after injection of coagulated autologous blood clots (0.3g/kg) in the superior vena cava. PV loops and PP loops were constructed with pressure and volume signals. The parameters of RV diastolic function were calculated from the PV and PP loops. Results: End-diastolic pressure and end-diastolic volume increased respectively from 3.40 ± 2.71 to 6.46 ± 2.36 mmHg (mean ± SD, p < 0.05) and from 60.73 ± 9.65 to 80.45 ± 3.72 ml (mean ± SD, p < 0.05), with no significant change in RV compliance (0,19 ±0.14 and 0.19 ± 0.10 ml/mmHg, mean ± SD). RV peak negative dP/dt extended from 0.39 ± 0.08 to 0.65 ± 0.01 mmHg/msec (mean ± SD, p < 0.01). Monoexponential decay time constant (Tau) did not show significant variation (37.85 ± 6.90 to 41.22 ± 13.98 msec, mean ± SD). The RV relaxation curve in the PP graph was nonlinear and was fitted with a quadratic function (dP/dt = A P2+B P+ dP/dt°). The curvilinearity coefficient (A) and the intercept (dP/dt°) did not change significantly but the second constant (B) significantly decreased from -40.30 ± 13.50 to -56.72 ± 11.60 sec-1 (mean ± SD, p < 0.01). Conclusions: As assessed by PP analysis, acute RV pressure overload by PE induces modifications in RV diastolic function. The right ventricle dilates and its diastolic filling pressure increases. Relaxation time constant calculated with monoexponential decay method, that considers linear relaxation of the ventricle, does not significantly changed. The relaxation curve in the PP graph, however, appears modified, as shown by the higher second constant of the fitted quadratic function. This reflects that the relaxation is non-uniform and that the non-uniformity is modified in acute PE in a such way that Tau would increase in early relaxation while it would decrease in late relaxation.

Reflecting and refracting modal correctors for compensation of large scale static and dynamic wave front aberrations in the lasers and image formation optical system have been developed and investigated. A grant attention was given to the problem of the thermal stability of the mirror surface. The new transparent type of corrector, namely, the active lens was proposed. The 20 channel compact and low-cost control system capable of interfacing with personal computer was developed.© (1999) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

Veiling Glare plays an important role in the performance of optical and electro-optical systems. It reduces the useful range of the instrument particularly when the object is situated against a bright background. The performance of Large aperture objective glasses and wide angle eye pieces coupled with electro-optical intensifiers used in low light level and other sighting systems, are dependent on the veiling glare index. The present paper reports a set up for measurement of veiling glare index for the systems having clear aperture as large as 250 mm and field of view upto 45o.

In this paper susceptibility of a microstrip transmission line as a simple PCB inside an enclosure is studied using the Finite Integral Technique (FIT). Here, the magnitude of transmission coefficient of a two port network model of the system (|S 21 |) is defined as the susceptibility of the PCB. The first port is the input port of a dipole antenna which propagates the interference wave and the second port is connected to a matched transmission line. The effect of different aperture size and numbers on |S 21 | is studied and it is shown that large apertures can even increase the disagreeable effects of the interfering wave on the PCB at resonance bandwidth of the perforated enclosure. To validate the results, measurements are performed inside an anechoic chamber.

An ultra-small (54 × 58 × 8.5 mm) and large aperture (1 × 7 mm) nine-color spectrometer—using an array of ten dichroic mirrors “biparted” as two layers—was developed and used for snapshot spectral imaging. Incident-light flux with a cross section smaller than the aperture size is split into nine color fluxes with 20-nm-width contiguous wavelength bands and central wavelengths of 530, 550, 570, 590, 610, 630, 650, 670, and 690 nm. Images of the nine color fluxes are simultaneously and efficiently measured by an image sensor. Unlike a conventional dichroic-mirror array, the developed dichroic-mirror array has a unique biparted configuration that not only increases the number of colors that can be measured simultaneously but also improves the image resolution of each color flux. The developed nine-color spectrometer was used for four-capillary-array electrophoresis. Eight dyes concurrently migrating in each capillary were simultaneously quantified by nine-color laser-induced fluorescence detection. Since the nine-color spectrometer is not only ultra-small and inexpensive but also has high light throughput and sufficient spectral resolution for most spectral-imaging applications, it has the potential to be widely used in various fields.

The depth of field (DoF) in photography is limited by the aperture size and focal length. When the focal length is definite, large aperture size leads to small DoF. In dark scene, we use a large aperture at the cost of deep DoF. The paper gives a detailed analysis of the focused plenoptic camera mode presented by Georgiev and Lumsdaine, and proposes a novel reconstruction algorithm. It recovers the image from radiance samples captured on the sensor and can get images of extended DoF to all-in-focus even with large aperture size. Beside, it can change the angle of view after the exposure. Depth of field of the rendered photo in this algorithm is also studied. The simulation result shows that under the assist of new algorithm, the DoF can be extended greatly.

Vertical cavity surface emitting lasers (VCSELs) with ultralow threshold and high efficiency have been fabricated using oxide apertures formed by selective oxidation of AlAs. Recent studies by Cheng et al. (1996) have shown that the expected reduction in threshold with aperture size is not achieved due to current spreading and lateral carrier diffusion even for rather large apertures (>5 /spl mu/m). To minimize these losses, we are exploring the use of a buried active region in VCSELs. To achieve the desired confinement in a buried heterostructure (BH) VCSEL, it is necessary to use selective area growth or regrowth of active region. Selective area epitaxy (SAE) also allows one to vary the cavity design locally by varying the masking pattern to achieve WDM arrays. SAE or regrowth must be done with tight regrowth process control to achieve very small thickness changes during the process and a low electrical and optical loss after regrowth. In this paper, we describe the impact of multiple step regrowth of device structures with Al containing layers on the luminescence and lasing characteristics of the resultant devices.