高斯光束经复合光学系统的聚焦特性

 讨论了高斯光束经由凹透镜，子系统和凸透镜构成的复合光学系统的聚焦特性，利用矩阵光学方法，推导出了高斯光束经复合光学系统聚焦后束腰宽度和像距的计算公式。计算例表明，选择适当参数的复合光学系统，既可以获得较小的束腰宽度，又可以获得较长的像距。     

Focusing of heat pulses along nonequilibrium nanowires

As a consequence of the temperature dependence of the speed of heat pulses, rectangular heat pulses will shrink (or extend) spatially, and will increase (or decrease) their temperature when propagating along a temperature gradient. Here, we consider heat pulse propagation along silicon nanowires, because of their interest in nanotechnology. The relative rates of variation per meter may be very high, and variations along relatively short lengths could be experimentally observable.     

Temporal and spectral properties of contra-propagating picosecond optical pulses in SOA

A useful analysis of contra-propagating optical pulses in semiconductor optical amplifier (SOA) is presented. Pulse temporal and spectral evolutions are investigated by resolving coupled equations describing pulse field propagation and SOA gain dynamics. With reference to the case of single pulse propagation, collision between pulses tends to maintain a good time-bandwidth product of amplified pulse and could provide a temporal compression by about 10% compared to pulse’s initial width.     

强场亚周期光脉冲研究

强场亚周期光脉冲的产生是未来激光光源发展所追求的先进内容之一,其不仅标志了超快激光技术的前进方向,并且将开启新型强场光与物质相互作用研究的大门。作为当前强场物理研究的一个重要课题——阿秒脉冲技术,强场亚周期光脉冲的出现将带给它新的发展机遇。强场亚周期光脉冲不仅可以直接产生极紫外波段孤立阿秒脉冲,而且其光电场的可裁剪性能够用来优化阿秒脉冲的产生。然而,亚周期光脉冲对应的超宽带光谱,使强场亚周期光脉冲的产生面临很大的挑战性。将多个中心波长不同的少周期超短脉冲进行合并的光场相干合成技术是实现强场亚周期光脉冲的有效技术。文章将介绍亚周期光脉冲的研究进展,着重描述基于光场相干合成技术的强场亚周期光脉冲产生方法。     

Focusing of wedge-generated higher-order optical vortices

We experimentally show that when higher-order optical vortices generated by a system of dielectric wedges are subjected to focusing they do not lose their structural stability.     

Imaging with short optical pulses

A new method of three-dimensional optical imaging based on range gating with subpicosecond pulses is being developed. As opposed to other techniques of medical imaging, this new method is characterized by both high contrast and resolution. Preliminary tests demonstrate a longitudinal resolution better than 10 μm. The computer algorithm needed to reconstruct the image from the attenuated backscattering and to extend to three dimensions the one-dimensional depth resolution, is discussed.     

Focusing in a largeF-number optical system

The true focal spot of a focusing system may be defined as either the location of the maximum on-axis intensity or the location of the minimum beam diameter that contains a certain fraction of the power. Diffraction causes this true focus to be shifted from the ideal geometrical optics prediction, the effect being greatest at largeF-numbers. Specifically, a theoretical and experimental study is made of the largeF-number focusing properties of a thin lens in contact with a uniformly illuminated aperture. The results are clarified by a comparison to the focal spot shift for a Gaussian beam.     

Synchronization of high-frequency chaotic optical pulses

Synchronization of high-frequency chaotic optical pulses is demonstrated in two semiconductor lasers with delayed optoelectronic feedback. The difference between synchronization and modulation is discussed. Evidence is presented to show that true synchronization, rather than modulation or amplification, is accomplished in our optoelectronic feedback system.     

Compression of amplified chirped optical pulses

We have demonstrated the amplification and subsequent recompression of optical chirped pulses. A system which produces 1.06 μm laser pulses widths of 2 ps and energies at the millijoule level is presented.     

卢卡斯光子筛的聚焦特性研究

介绍了一种基于卢卡斯数编码设计的轴上四焦点光子筛,其各焦距分布与黄金分割比密切相关.实验上利用相移数字全息验证了设计器件具有轴上四焦点聚焦特性,测量结果表明:轴向焦距和横向焦斑光强分布与理论设计值一致.该振幅型光子筛具有体积小、重量轻、易加工等优点,可应用于X波段显微和生物细胞阵列成像等领域.     

Nonlinear optical properties of an azo-based dye irradiated by picosecond and nanosecond laser pulses

The nonlinear optical properties of an azo-based dye were investigated using Z-scan technique employing 38 ps pulses at 532 and 1064 nm, and 6 ns laser pulses at 532 nm. Large nonlinear absorption and nonlinear refraction were observed at both ps and ns 532 nm in the azoic dye. When excited at ps 1064 nm, this dye displayed a large two-photon absorption cross-section (σ₂=1810 GM). Meanwhile, the optical nonlinearity mechanism was discussed in terms of molecular structure, excitation wavelength, and pulse width.     

Focusing properties of small lenses

The potential use of small substrate lenses for coupling to antennas at millimeter wave frequencies is investigated by analyzing the focusing properties of dielectric spheres with quarter-wave matching layers. The fields and the power density are calculated at various points within the sphere to learn how the focusing deteriorates as the lens is made smaller. The absorption loss of the lens is also calculated. The calculations show that quartz spheres with quarter-wave matching layers, can exhibit good focusing properties down to a radius of about half a free space wavelength. This minimum radius was found to increase almost linearly with the refractive index of the lens. The calculations also indicate that at 94GHz the absorption losses of fused quartz, silicon and gallium arsenide lenses, with radii of one free space wavelength or less, are less than 0.2 dB. As the minimum diameter of a quartz lens is comparable with the spot size in free space, it should be possible to build an imaging lens array in which each lens will act as a separate imaging element.     

Switching pulses for an optical transistor

We study the characteristics of a rectangular pulse used to switch an optical transistor. Three regimes appear. (i) For low intensity pulses, the pulse duration and area decrease exponentially with increasing holding intensity. (ii) For high intensity pulses, the pulse duration and area decrease linearly with increasing holding intensity. (iii) For a holding intensity near the transition region, the only constraint is on the pulse area and not on its duration or intensity separately.     

Self-induced transparency of very short optical pulses

Solutions to a first order wave equation, appropriate to ultrashort optical pulse theory and to the optical undamped Bloch equations are presented. Detuning is shown to play essential role in the physical interpretation of these solutions. Related cases have been discussed by Courtens and by Lee. It is noted that the rotating wave approximation introduces strong restrictions on the range of validity of possible solutions. Pulses with Lorentzian shapes, while implied by the equations, appear to be without physical significance.     

Storage of intense optical pulses in solids

Possibility to store optical information in media with fast relaxations is studied in case of arbitrary intensities of probe and control pulses. Analytical solution of the self-consistent system of equations for propagation and density matrix is obtained with allowance for the first non-stationary corrections. A new scheme of storage is proposed which allows an essential reduction of the optical length needed for storage.     

Spectrum control and shaping of optical pulses in optical fibre interferometers

This paper discusses the use of single-mode fibre ring interferometers for injection laser line narrowing and for enhancement of optical emission power. The efficient launching into fibre ring interferometers of multi-frequency external cavity injection laser emission, in both the c.w. and mode-locking regime, has been achieved. Matching the optical lengths of the external cavity and fibre interferometer allowed the measurement of mode width of such a laser. A method is proposed for shaping optical pulses in fibre ring interferometers from constant intensity frequency modulated emission. The mode-locking regime of all-fibre external cavity injection lasers has been achieved.