Improvements in confocal microscopy imaging using serrated divided apertures

Confocal microscopy with serrated divided apertures is presented. Compared with using two smooth D-shaped apertures in confocal microscopy, the serrated divided apertures can suppress the out-of-focus central bright spot, thus increasing the efficiency of rejection of scattered light. Diffraction analysis shows that the serrated apertures maintain the optical sectioning strength while attenuating the background coming from far from the focal plane. In addition, the signal to background ratio (S/B) is also improved.     

Terahertz near-field imaging using subwavelength plasmonic apertures and a quantum cascade laser source

The first demonstration, to our knowledge, of near-field imaging using subwavelength plasmonic apertures with a terahertz quantum cascade laser source is presented. "Bull's-eye" apertures, featuring subwavelength circular apertures flanked by periodic annular corrugations were created using a novel fabrication method. A fivefold increase in intensity was observed for plasmonic apertures over plain apertures of the same diameter. Detailed studies of the transmitted beam profiles were undertaken for apertures with both planarized and corrugated exit facets, with the former producing spatially uniform intensity profiles and subwavelength spatial resolution. Finally, a proof-of-concept imaging experiment is presented, where an inhomogeneous pharmaceutical drug coating is investigated.     

通过有光阑近轴ABCD光学系统激光束的近似解析传输公式

 用傅立叶级数展开法研究光束通过有光阑限制的近轴ABCD光学系统的传输特性，导出了光阑透射率函数不同时的传输公式。硬边光阑的情况可作为其它光阑的特例得到，其它光阑也可视作硬边光阑来处理。数值计算表明了该方法快速的优点，并得到与用Collins公式直接积分一致结果。     

Delay in light transmission through small apertures

We demonstrate a technique for measuring pulse propagation time delays with 0.5-fs resolution by use of a widely available 100-fs pulsed laser. Using this technique, we measured the time delay of a light pulse transiting through subwavelength apertures placed on a 0.3-mum metallic film. We measured a 7-fs total transit time, corresponding to an effective group velocity of c/7 . The experimental result yielded additional evidence that light interacts resonantly with oscillators formed by the surface modes near the small apertures.     

Experimental verification of coherent diffractive imaging by a direct phase retrieval method with an aperture-array filter

Recently, we have proposed a coherent diffractive imaging using a noniterative phase retrieval method with the filter of an aperture array. The first (to our knowledge) experimental demonstration of this coherent imaging is presented here, in which a complex-valued object illuminated by a diode laser is reconstructed from the isolated diffraction intensities of the object's wave field, transmitted through an array filter of square apertures by using the phase retrieval method. This imaging method requires only a single measurement of the diffraction intensity and does not need a tight object's support constraint utilized in iterative phase retrieval algorithms or a reference wave used in holographic techniques.     

A slow-light laser radar system with two-dimensional scanning

We propose a multi-aperture slow-light laser radar with two-dimensional scanning. We demonstrate experimentally that we can use two independent slow-light mechanisms, namely dispersive delay and stimulated Brillouin scattering, to dynamically compensate the group delay mismatch among different apertures, while we use optical phase locking to control the relative phases of the optical signals emitted from different apertures, as the system steers the beam in two dimensions.     

Slanted hole array beam profiler (SHArP)-a high-resolution portable beam profiler based on a linear aperture array

We demonstrate a novel high-resolution portable beam profiler based on a slanted linear array of small apertures, termed a slanted hole array beam profiler (SHArP). The apertures are directly fabricated on a metal-coated CMOS imaging sensor. With a single linear scan, the aperture array can establish a virtual grid of sampling points for beam profiling. With our prototype, we demonstrate beam profiling of Gaussian beams over an area of 66.5 microm x 66.5 microm with a resolution of 0.8 microm (compare with the CMOS pixel size of 10 microm). The resolution can be improved into the range of submicrometers by fabricating smaller apertures. The good correspondence between the measured and calculated beam profiles proves the fidelity of our new beam profiling scheme.     

阵列口径Nd：YAG片状激光器重复频率输出特性研究

 介绍了一种新型阵列口径的固体片状激光器的设计及初步实验，研究了其激光输出特性。激光器采用2×1阵列的以布儒斯特角放置的片状Nd:YAG激光头模块，并采用氙灯泵浦方式，由平均功率为60 kW电池组电源供电；电源采用大电流恒流放电，对输出放电进行可编程控制。实验得到32 J的单脉冲输出，小信号增益系数为0.047 5 cm^-1；泵浦单脉冲运行，脉宽为1~5 ms时，输出能量呈线性增长；当重复频率为20 Hz时，5 ms脉宽比1 ms脉宽输出功率下降30%，其原因是布儒斯特角结构存在时，由热应力引起的热致双折射损耗造成输出下降。     

One-dimensional Doppler laser collimation of chromium beam with a novel pre-collimating scheme

A novel pre-collimating scheme in laser-focused chromium (Cr) atomic deposition is presented. It consists of three apertures, which are one main pre-collimating aperture at centre and two probing apertures with uniform dimension at both sides of the central one. The calculations show that the Cr atomic beam is divided into three parts accordingly after going through this scheme, and the full-width at half-maximum (FWHM) of each part decreases while the peak value increases after one-dimensional (lD) Doppler laser collimation, subsequently. Compared with that before laser collimation, the central part does not have displacement, but each part of the other two has the same displacement to the centre after laser collimation. These phenomena which are agreed with experiment prove that the novel pre-collimating scheme is a feasible means to solve the problem which we cannot observe the collimation of Cr atomic beam after substrate in laser-focused deposition with a pre-collimating scheme of only one aperture, because the atoms will be obstructed completely by the substrate.     

Status of single-model optical fiber standardization in the electronic industries association (EIA)

This paper introduces and analyzes revolutionary laser system architecture capable of dramatically reducing the complexity of laser systems while simultaneously increasing capability. The architecture includes three major subsystems. The first is a phased array of laser sources. In this article, we discuss diode-pumped fiber lasers as the elements of the phased array, although other waveguide lasers can also be considered. The second provides wavefront control and electronics beam steering, as described in an IEEE Proceedings article on “Optical Phased Array Technology” [1]. The third is subaperture receiver technology. Combining these three technologies into a new laser systems architecture results in a system that has graceful degradation, can steer to as wide an angle as individual optical phased array subapertures, and can be scaled to high power and large apertures through phasing of a number of subapertures. Diode-pumped fiber lasers are appealing as laser sources because they are electrically pumped, efficient, relatively simple, and scalable to significant power levels (over 100 Watts has been demonstrated from a single diode-pumped fiber laser) [2]. The fiber laser design also lends itself to integration into a phased array. Fiber lasers have been phased. Initial phasing demonstrations have been at low power and were conducted by taking a single source, dividing it into multiple fibers, then phasing them together. To develop this technology further we need to use independent fiber lasers or fiber amplifiers, seeded by a common source, and to increase laser power. As we increase laser power, we will have to learn to cope with nonlinearities in the laser amplifiers. Optical Phased Array technology has demonstrated steering over a 90-degree field of regard [4], although this approach used additional optical components. If we use straightforward optical phased array beam steering without additional optics we can steer with high efficiency to about one-third λ/d, where d is the smallest individually addressable element. The one-third factor depends on the efficiency threshold. For example, if we use 1.5 μm light, and 5 μm center-to-center spacing, we can steer with high efficiency to about ±6 degrees, or a field of regard of 12 degrees. Last, we need to develop a subaperture receive technology. This can be a pupil plane receiver, an image plane receiver, or some combination of the approaches. When we have matured each individual technology and combined them into new laser systems architectures, we will have the ability to build simpler and more capable laser systems. The vision for an integrated, phased array laser concept is to enable a new class of laser systems with significant advantages, including high-efficiency, all-electric laser source; all waveguide beam transport; wavefront control at the sub-aperture level (enabling wavefront compensation, conformal apertures, and wide-angle electronic beam steering); random access beam pointing over wide angles; multiple simultaneous beam generation and control; and graceful degradation.     

Optical generator of spheroidal wave functions,using a BSO crystal

We recall that the oscillating modes of an optical confocal resonator are typically spheroidal. These modes can be physically obtained when a light amplifier is introduced within such a resonator. In this paper, we present some particularities of amplification by a BSO crystal compared with amplification by stimulated emission of radiations (laser). We then present some spheroidal modes, obtained with a BSO ring oscillator when circular or rectangular apertures are used.     

激光在湍流大气中的干涉仿真

通过研究激光在湍流大气中的传输情况，旨在为光学高分辨率干涉成像提供理论依据。采用相位屏的近似处理方法对激光通过大气湍流传输进行模拟，研究激光通过湍流大气的干涉情况。试验结果表明：孔径间距越大，干涉条纹越密；在传输距离为2km，大气湍流折射率结构常数C2n为10-14，即接近强湍流的情况下，可以形成比较好的干涉条纹。孔径间距较小时，干涉的明暗条纹清晰可见。在实际干涉成像中，可以选择适当的孔径间距来获得较好的干涉条纹，从而获得目标的高分辨率像。     

激光显示照明光路中复眼透镜的设计

设计激光投影机光学系统需要从如何减小光学系统的体积和提高激光光源的光效两个方面考虑。研究了激光显示照明系统中的复眼透镜,并对设计的复眼小透镜矩形单元进行了优化,发现在复眼透镜整体尺寸和单颗复眼小透镜焦距一定的情况下,整个复眼透镜上的阵列越多,即复眼透镜上蜂窝的数量越多,其匀光效果就越好,且此时投影机系统的体积也较小。为了提高激光光源的光效,设计中对复眼透镜在不同数值孔径照明光束下的匀光效果进行了讨论。并对优化设计后的复眼透镜进行40 000条光线追迹,实验显示其光线透过率可以达到92.5%,且几乎无杂散光。     

Perfectly phase-matched third-order distributed feedback terahertz quantum-cascade lasers

We report a novel laser cavity design in third-order distributed feedback (DFB) terahertz quantum-cascade lasers based on a perfectly phase-matching technique. This approach substantially increases the usable length of the third-order DFB laser and leads to narrow beam patterns. Single frequency emissions from 151 apertures (5.6 mm long device) are coherently added up to form a narrow beam with (FWHM≈6×11°) divergence. A similar device with 40 apertures shows more than 5 mW of optical power with slope efficiency ～140 mW/A at 10 K pulsed operation.     

High order harmonic generation optimization with an apertured laser beam

We report a systematic study of high order harmonic generation with an infrared laser apertured by an iris, as a function of the aperture size. Measurements were made of harmonic generation efficiency for different gas species, laser energies and focal geometries. Harmonic efficiencies as a function of aperture show a characteristic peaked shape, which is independent of gas species and harmonic order. A one dimensional, time dependent simulation of harmonic generation in a gas cell, taking into account experimentally measured transverse coherence of the laser, closely reproduces the observed behaviours. We show that the aperture diameter which maximizes harmonic yield is the result of a compromise between considerations of focal geometry and ionization (which favour small apertures); and harmonic dipole amplitude and phase (which favour large apertures). Received 31 May 2002 Published online 24 September 2002 RID="a" ID="a"e-mail: kazamias@ensta.fr RID="b" ID="b"UMR 7639 du CNRS     

Third harmonic generation by ultrashort laser pulses tightly focused in air

The influence of focusing conditions (numerical apertures from 0.004 to 0.06) on absolute energetic characteristics of third harmonic generation (THG) in air was experimentally studied for pumping 1R (744 nm wavelength) femtosecond laser pulses. THG was observed both for sub-critical and super-critical laser pulses in the linear and non-linear propagation modes, respectively. The maximum THG efficiency of 1.6 × 10⁻³ was obtained in our experiments at the tight focusing conditions and the sub-critical pulse powers.     

腔内倾斜标准具法压缩KrF激光线宽的研究

我们对采用腔内倾斜标准具法压缩激光线宽进行了研究，较详细地讨论了影响线宽压缩效果的各种因素。并在一台长脉冲放电泵浦ＫｒＦ准分子激光器上，采用三个标准具作为线宽压缩元件，获得了线宽小于３ＧＨｚ，发散角近似衍射极限的高质ＫｒＦ激光输出。实验中研究了不同光阑孔径及输出耦合率对输出线宽和输出能量的影响。     

Self-organized nanostructure by a femtosecond laser on silicon

In this paper, ripple structure and hole arrays were investigated. Techniques based on laser scanning microscopes for the processing of periodic structures on silicon with a femtosecond laser (800 nm, 1 kHz, 130 fs) had been used. Ripples and any holes were obtained after laser irradiation in air with S and P polarization. The effect of the scanning speed (v) and the lens with different numerical apertures (NA) on the laser-induced surface topography were studied. We found that the femtosecond laser produces periodic ripples on the silicon surface of the submicron level, the width of line has a tight relationship to the NA and scanning speed. Finally, we process the microapparatus on silicon, for which the wide channel was 800 nm.     

Effects of excimer laser illumination on microdrilling into an oblique polymer surface

In this work, we present the experimental results of micromachining into polymethy-methacrylate exposed to oblique KrF excimer laser beams. The results of low-aspect-ratio ablations show that the ablation rate decreases monotonously with the increase of incident angle for various fluences. The ablation rate of high-aspect-ratio drilling with opening center on the focal plane is almost independent of incident angles and is less than that of low-aspect-ratio ablation. The results of high-aspect-ratio ablations show that the openings of the holes at a distance from the focal plane are enlarged and their edges are blurred. Besides, the depth of a hole in the samples oblique to the laser beam at a distance from the focal plane decreases with the increase of the distance from the focal plane. The number of deep holes generated by oblique laser beams through a matrix of apertures decreases with the increase of incident angle. Those phenomena reveal the influence of the local light intensity on microdrilling into an oblique surface.     

Near-field hexagonal array illumination based on fractional Talbot effect

Hexagonal array is a basic structure widely exists in nature and adopted by optoelectronic device. A phase plate based on the fractional Talbot effect that converts a single expanded laser beam into a regular hexagonal array of uniformly illuminated apertures with virtually 100% efficiency is presented. The uniform hexagonal array illumination with a fill factor of 1/12 is demonstrated by the computer simulation.