二元位相匹配衍射透镜的研究与应用

针对大数值孔径衍射透镜制作难、衍射效率低的问题，探讨了用位相匹配原理对元件结构参数优化设计的方法，研制出８台阶二元衍射位相匹配透镜列阵，达到了预期的效果。采用该方法设计的大数值孔径红外锗透镜和为光聚能器，应用在提高红外探测器性能的实验中。     

Wave Theory for a Simple Lens

A new wave theory describing image formation by a simple lens is formulated in the angular spectrum representation. It is closely related to Luneburg's theory of instrumental optics but is free of certain geometrical approximations made in his theory. The validity of Luneburg's essentially geometrical treatment of the lens aperture is discussed and the approximations involved are found to be justified for isoplanatic optical systems with small numerical aperture. Some concepts usually found in lens theories based on geometrical optics are seen to have analogues in the present wave theory. In particular, a connection is made between homogeneous plane waves in an angular spectrum expansion of the field and the light rays belonging to a family of rays that pass through the lens. The fundamental relations assumed in Fourier optics are shown to follow from this theory when they are applied to the special case of isoplanatic optical systems with small numerical aperture. The image field of a scalar dipole formed by a diffraction-limited lens is calculated using these results.     

Changes of intensity distribution of a tightly focused plane-wave pulse induced by lens dispersion

The tightly focusing properties of a linearly polarized plane-wave pulse through a high numerical aperture (NA) lens with dispersion are formulated. The effects of lens dispersion on the tightly focused intensity distribution in the focal region are studied in detail. It is found that, because of the lens dispersion, the intensity of the side lobe of the focused light spot strengthens in the transverse direction and the size of the main lobe of the focused light spot increases in the longitudinal direction as the pulse duration decreases. In addition, we compare the effects of dispersion of lens made by different types of glass on tightly focusing properties of a pulse beam. The results will be helpful to choose suitable high NA objective lens in experiment.     

Phase retrieval from diffraction intensities by use of a scanning slit aperture

A noniterative method of retrieving the phase of a wave field from intensities measured during scanning of a slit aperture is proposed. In the measurements, one records the diffraction intensities of wave fields transmitted through a slit that is scanned along two directions in the Fresnel-zone plane of an object's field. From these intensities, the phase in the Fresnel-zone plane can be retrieved by a method in which a novel phase calculation technique that uses Fourier transforms is included. Because the method does not require lens systems, it provides a potentially useful means for coherent imaging by use of x rays, electrons, or nuclear particles.     

Blue/DVD/CD compatible optical head

Compatibility with Digital Versatile Disc and Compact Disc has been demonstrated for two options of high-density optical disk systems using a blue laser diode. Option 1 (HD DVD) employs a 0.65 numerical aperture objective lens and a 0.6 mm thick protective layer disk, while Option 2 (Blu-ray Disc) employs a 0.85 numerical aperture objective lens and a 0.1 mm thick protective layer disk. An optical head has three laser diodes whose wavelengths are 405 nm, 660 nm, and 785 nm. A spherical aberration caused by the difference in the protective layer thickness of the disk is corrected by an objective lens magnification change, while the numerical aperture of the objective lens is controlled by a wavelength-selective aperture. Experimental results have shown that Option 1 is more preferable, but Option 2 is also acceptable from the viewpoint of the compatibility.     

High-aperture diffraction of a scalar, off-axis Gaussian beam

A scalar treatment for Gaussian beams offset from the optic axis and then focused by a high-numerical-aperture lens is presented. Such a theory is required for describing certain types of Doppler microscopes, i.e., when the measurement is simultaneously performed by more than a single beam axially offset and then focused by a lens. Analytic expressions for the intensity in the focal region of the high-aperture lens are derived. From these expressions we calculate the intensity in the focal region with parameters of beam size, beam offset, and the numerical aperture of the lens. The relative location and variation of the intensity around the focal region are discussed in detail. We show that for small-diameter Gaussian beams the Strehl ratio increases above unity as the beam is offset from the optic axis. This is explained by the increase in the effective numerical aperture of the offset beam compared with the one collinear with the optic axis. From examining the focal distribution, we conclude that it rotates for small beam size and that increasing beam diameter causes the focused distribution to rotate and shear, i.e., to distort. We also show that the distortion of the distribution increases with increasing numerical aperture.     

Nonadiabatic chemoelectron energy conversion in heterostructures for hydrogen power engineering

A relationship describing the probability of electron excitation in a solid crystal by the energy of a chemical reaction on its surface has been found. It is established that the probability of electron excitation in this reaction exponentially increases with decreasing energy of electron transition in the solid. A method of nonadiabatic chemoelectron energy conversion in heterostructures for hydrogen power engineering based on Schottky diodes is proposed and the efficiency of this method is calculated.     

远距离高精度多普勒位移测量

通过泛函、激光散斑理论和随机过程各态遍历的研究,导出激光多普勒信号强度与聚焦光斑直径、接收透镜通光口径、光电接收器响应等参数间的关系,在此基础上设计出一种适用于远距离处面内位移测量的光路。此光路将高斯光束束腰聚焦在被测体上,实现最小聚焦光斑和平面波叠加,此外采用大口径透镜接收散射光,用响应度高的光电接收器转换光电信号等措施获得高强度高信噪比的测量信号。将此光路用于 100m 处面内位移(49.70mm)测量,其精度可达 2%。此设计方法能用于振动或地震波的高精度检测。     

Probing acoustic fields of clinically relevant transducers: the effect of hydrophone probes' finite apertures and bandwidths

The influence of finite aperture and frequency response of piezoelectric ultrasonic hydrophone probes on the free-field pulse intensity integral (PII) and mechanical index (MI) was investigated using a comprehensive acoustic wave propagation model. The model developed was capable of predicting the true pressure-time waveforms at virtually any point in the field. The input to the model used pressure amplitude data measured in the immediate vicinity of the acoustic source or transducer considered. The experimental verification of the model was obtained using a commercially available, 8 MHz, dynamically focused linear array and a single element, 5 MHz, focused rectangular source. The verification was performed at low and high excitation levels, corresponding to linear and nonlinear acoustic wave propagation, respectively. The pressure-time waveforms were recorded using piezoelectric polymer hydrophone probes that had different sensitivities, frequency responses, bandwidths, and active element diameters. The nominal diameters of the probes ranged from 50 to 500 microm, and their useable bandwidths varied between 55 and 100 MHz. The PII, used to calculate the thermal index (TI), was found to increase with increasing bandwidth and decreasing effective aperture of the probes. The MI, another safety indicator, also was affected, but to a lesser extent. The corrections predicted using the model were used to reduce discrepancies as large as 30% in the determination of PII. The results of this work indicate that, by accounting for hydrophones' finite aperture and correcting the value of PII, all intensities derived from the PII can be corrected for spatial averaging error. The results also point out that caution should be exercised when comparing acoustic output data. In particular, hydrophone's frequency characteristics of the effective diameter and sensitivity are needed to correctly determine the MI, TI, and the total acoustic output power produced by an imaging transducer.     

Excitation with a focused, pulsed optical beam in scattering media: diffraction effects

To gain a better understanding of the spatiotemporal problems that are encountered in two-photon excitation fluorescence imaging through highly scattering media, we investigate how diffraction affects the three-dimensional intensity distribution of a focused, pulsed optical beam propagating inside a scattering medium. In practice, the full potential of the two-photon excitation fluorescence imaging is unrealized at long scattering depths, owing to the unwanted temporal and spatial broadening of the femtosecond excitation light pulse that reduces the energy density at the geometric focus while it increases the excitation energy density in the out-of-focus regions. To analyze the excitation intensity distribution, we modify the Monte Carlo-based photon-transport model to a semi-quantum-mechanical representation that combines the wave properties of light with the particle behavior of the propagating photons. In our model the propagating photon is represented by a plane wave with its propagation direction in the scattering medium determined by the Monte Carlo technique. The intensity distribution in the focal region is given by the square of the linear superposition of the various plane waves that arrive at different incident angles and optical path lengths. In the absence of scattering, the propagation model yields the intensity distribution that is predicted by the Huygens-Fresnel principle. We quantify the decrease of the energy density delivered at the geometric focus as a function of the optical depth to the mean-free-path ratio that yields the average number of scattering events that a photon encounters as it propagates toward the focus. Both isotropic and anisotropic scattering media are considered. Three values for the numerical aperture (NA) of the focusing lens are considered: NA = 0.25, 0.5, 0.75.     

Study on Reducing the Size-of-Source Effect of Pyrometers

The size-of-source effect (SSE) is an important uncertainty source in radiation thermometry when radiation targets with different sizes are measured. In this article, a test pyrometer was established to study the way to reduce the SSE. The most dominant factors that influence the SSE, include the quality and surface condition of the objective lens, the placement and diameter of the aperture stop, and the inner baffles. Through an optimized lens and redesign of the aperture stop and baffles, the SSE of the test pyrometer is reduced to 2 × 10^?4 when a 50 mm diameter radiance source with a 4 mm diameter central obscuration is used. The improvement method is applied to the primary standard pyrometer for which the SSE is reduced to less than 1 × 10^?4.     

Propagation and backpropagation for ultrasonic wavefront design

Wave backpropagation is a concept that can be used to calculate the excitation signals for an array with programmable transmit waveforms to produce a specified field that has no significant evanescent wave components. This concept can also be used to find the field at a distance away from an aperture based on measurements made in the aperture. For a uniform medium, three methods exist for the calculation of wave propagation and backpropagation: the diffraction integral method, the angular spectrum method, and the shift-and-add method. The boundary conditions that are usually implicitly assumed by these methods are analyzed, and the relationship between these methods are explored. The application of the angular spectrum method to other kinds of boundary conditions is discussed, as is the relationship between wave backpropagation, phase conjugation, and the time-reversal mirror. Wave backpropagation is used, as an example, to calculate the excitation signals for a ring transducer to produce a specified pulsatile plane wave with a limited spatial extent.     

Variation on Zernike's phase-contrast microscope

We describe the design, construction, and testing of a variant of Zernike's phase-contrast microscope. The sample is illuminated with a white-light source through an annular aperture, which is projected onto the entrance pupil of the objective lens. In the return path the light diffracted by the sample and appearing in the interior of the objective's aperture (i.e., the test beam) is separated from the light returning in the annular region near the rim of the objective (i.e., the reference beam). The separated beams are relatively phase shifted and then combined to create an interferogram of the sample's surface on a CCD camera. It is fairly straightforward to use this system as a conventional bright-field or dark-field microscope, but its most interesting application is as a Zernike phase-contrast microscope with adjustable amplitude ratio and phase shift between test and reference beams. The ability to continuously adjust the phase of the reference beam also enables quantitative measurement of the phase imparted by the sample to the incident beam.     

Approximating the ITS-90 between Zinc and Copper with an Infrared Thermometer at NIS-Egypt

This paper presents an approximation to the International Temperature Scale of 1990 (ITS-90) between the Zn (420 °C) and Cu (1085 °C) fixed points using a 900 nm narrow-band radiation thermometer. This thermometer has a 400 mm working distance and a 150 mm objective focal length. An image of the measured target is focused by the objective lens onto a 1 mm aperture (drilled mirror). The light passing through the aperture is conveyed by a condenser lens through an interference filter with a nominal central wavelength of 900 nm and a half-bandwidth of 10 nm before reaching a silicon photodiode working in the photovoltaic mode. The thermometer was calibrated at the Zn, Al, Ag, and Cu blackbody fixed points. The results of the calibration were used to determine the constants A, B, and C of the Sakuma-Hattori interpolation equation. The results showed that the ITS-90 can be approximated within ± 0.051 °C throughout the Zn-Cu interval when the thermometer is calibrated at the Zn, Al, Ag, and Cu fixed points.     

Characterization of gradient-index lens-fiber spacing toward applications in two-photon fluorescence endoscopy

We report on the experimental investigation into the characterization of two-photon fluorescence microscopy based on the separation distance of a single-mode optical fiber coupler and a gradient-index (GRIN) rod lens. The collected two-photon fluorescence signal exhibits a maximum intensity at a defined separation distance (gap length) where the increasing effective excitation numerical aperture is balanced by the decreasing confocal emission collection. A maximum signal is found at gap lengths of approximately 2, 1.25, and 1.75 mm for GRIN lenses with pitches of 0.23, 0.25, and 0.29 wavelength at 830 nm. The maximum two-photon fluorescence signal collected corresponds to a threefold reduction of axial resolution (38.5 microm at 1.25 mm), compared with the maximum resolution (11.6 microm at 5.5 mm), as shown by the three-dimensional imaging of 10 microm beads. These results demonstrate an intrinsic trade-off between signal collection and axial resolution.     

Focal shifts in focused nonuniformly polarized beams.

We present a simple formula to evaluate the relative focal shift in a circular-aperture lens system illuminated by a nonuniformly polarized (NUP) light wave. Specifically, it is shown that the relative focal shift is determined by the effective Fresnel number. The effective Fresnel number is equal to the product of the Fresnel number of the lens aperture and the parameter sigma, which describes the uniformity of the polarization distribution of the NUP beam across the lens aperture. Some examples are given to illustrate the use of this approach. The influence of the polarization distribution of the incident NUP light wave on the polarization distribution in the axial points of the focused field is also presented.     

厄米双曲余弦高斯光束的焦开关

对双曲余弦高斯光束通过光阑透镜分离系统的轴上光强分布做了详细的数值分析。研究发现,在一定条件下轴上存在两个光强极大值点,并且在这两个极大值点相互竞争中会出现焦点位置的有效置换,即出现焦开关。厄米双曲余弦高斯光束产生焦开关的条件是:光阑与透镜相对间距为1,光束阶数为偶数,光束参数小于其相应的临界值,截断参数在它的两个临界值之间。进一步研究表明,焦点位置相对跃迁量和轴上相对光强下凹量随光束参数的减小而增大,但是随着截断参数的增大焦点位置相对跃迁量和轴上相对光强下凹量将分别出现一个极大值。在大范围调焦的应用中,可利用焦开关实现调焦之目的;在精密聚焦的激光应用中,应控制焦开关的产生。     

Longitudinal–differential phase distribution near the focus of a high numerical aperture lens: study of wavefront spacing and Gouy phase

The longitudinal–differential (LD) phase distribution was investigated near the focus of a high numerical aperture (NA = 0.9) aplanatic lens illuminated with a linearly polarized monochromatic plane wave. The Richards and Wolf method was used to compute field distributions. The LD phase map was obtained by analyzing the deviation of the phase of the simulated wave to the phase of a referential plane wave. The irregular wavefront spacing that is linked to the Guoy phase is discussed and subtle details of the phase features with respect to the spatial domain relative to the focal point are disclosed. The LD phase is used to revisit different definitions of the focal region. The definition is eventually identified that is in agreement with the Gouy phase in the focal region. Our work paves the way towards a coherent notion to quantify the optical action of high NA optical elements that are increasingly important for many applications.     

Performance of Apodized Apertures under Partially Coherent Illumination

The performance characteristics of optical systems having apodized apertures and employing partially coherent illumination have been investigated. The pupil function has been taken to be of the form f(x y) = 1 m g (x 2 + y 2), where g is the amplitude shading parameter of the filter. The generalized cross-transfer functions for the system have been calculated for different values of the coherence parameter which is the ratio of the numerical aperture of the condenser to that of the objective. The modulations of periodic targets commonly employed, namely, the sine wave, square wave and triangular wave objects, have also been investigated. It has been shown that for the partially coherent and the incoherent illuminations ( S 1) the apodization improves the low frequency response at a cost of the high frequency response of the system. However, for coherent and near coherent illuminations (