共查询到20条相似文献,搜索用时 15 毫秒
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有振幅调制和相位畸变光束通过硬边光阑的M2因子 总被引:5,自引:3,他引:2
光束传输M^2因子是表征激光束的有用参量。利用矩形函数的复高斯函数的近似展开方法,给出部分相干光通过硬边光阑后强度二阶矩的近似计算公式,由此可得到部分相干光通过硬边光阑后的推广M^2因子。以有振幅调制和相位畸变光束为例,推导出相应的推广M^2因子的解析表达式,通过数值计算对提出的近似算法的计算精度进行了分析。研究结果表明,使用该近似方法计算得到的推广M^2因子的计算误差小于1%,且通过该方法可直接得到相应的近似解析计算公式,从而使计算得以简化,并有效地提高了计算效率。 相似文献
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The pressure sensitivity of a laboratory standard microphone is determined using a reciprocity technique that measures the electrical transfer impedance of two microphones connected acoustically by a coupler. The electrical transfer impedance is a function of the coupler volume and the equivalent volumes of the microphones. The equivalent volume given as a function of the frequency can be determined in experiments or can be calculated if the equivalent volume at a low frequency as well as the resonance frequency and loss factor of the microphone diaphragm are known. Therefore, it is necessary to determine the resonance frequency and the loss factor accurately to obtain an accurate reading of the pressure sensitivity.In this paper, a new method to determine the resonance frequency and loss factor of a microphone diaphragm is proposed. The frequency response of the diaphragm displacement is measured by a laser vibrometer and the part of the response near the resonance frequency is used to determine the microphone parameters via least square fitting with the equation of a vibration model with one degree-of-freedom. Since the values measured by this method are close to the nominal values and the repeatability is highly feasible, the proposed method will be useful to determine the resonance frequency and loss factor of a microphone diaphragm. 相似文献
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在自锁模飞秒钛宝石激光器运转状态不变的条件下,仅仅改变所加光阑,便可获得三波长或双波长的飞秒光脉冲运转.在此基础上,我们比较了这两种运转状态下激光器输出脉冲的脉宽,啁啾、中心波长间距和输出功率的差异.给出了在不同条件下运转时的双波长激光器的输出特性.讨论了多波长运转时的一些规律. 相似文献
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V. S. Dneprovskii E. A. Zhukov M. V. Kozlova A. M. Smirnov T. Wumaier 《Moscow University Physics Bulletin》2012,67(2):201-207
The features of the nonlinear absorption of CdSe/ZnS quantum dots (colloidal solution) in the case of resonant one- and two-photon excitation of the basic exciton transition by powerful ultra-short laser pulses were determined. In one-photon excitation, with an increasing intensity of impulses, a decrease in absorption (bleaching) is relayed by an increase in absorption, which is associated with the process of the filling of the states (saturation) of a two-level system with the lifetime of the excited state depending on the light intensity. The arising Fresnel or Fraunhofer diffraction of the laser ray that pass through a colloidal solution with a high concentration of quantum dots is associated with the formation of the transparency channel and self-diffraction of laser ray on an induced diaphragm. In two-photon excitation, the features of the nonlinear absorption and luminescence tracks (the dependence of luminescence intensity on distance) were explained by the influence, in addition to the two-photon absorption, of the processes that are responsible for the slower growth of nonlinear absorption and luminescence quenching at high intensities of laser pulses. 相似文献
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Wide range of applications using He–Ne laser were carried out employing speaker for vibration modulation. The very simple method was achieved by gluing a mirror to the diaphragm of an ordinary miniature speaker. The technique allows many of the applications that depend on laser absorption coincidences to be performed by a He–Ne laser enhancing by the range of applications in which it can be used and avoiding the complications and expenses needed for sophisticated equipment. Speaker modulation was found efficient and comparable to mechanical chopper modulation. The method is sensitive enough to determine minute changes in index of refraction or transparent material thickness change and suitable for odor emission monitor. 相似文献
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351nm波长的准分子激光器由光波导管作为激光均束器,直接输出正六角形均匀分布的照明光束,能在大面积激光投影光刻中实现无缝扫描。同目前常用的微透镜阵列器相比制作简单,无须光阑就能直接获取所需要的六角形光束,减少了能量损失。通过合理的假设和理论推算,依据管内最大反射次数就能适当地选取光波导管的长度,既保证了足够的反射次数以维持良好的均匀性,同时又避免了不必要的管长所带来的更多反射损耗。利用ZEMAX光学设计软件模拟和分析了由光波导管输出的照明光。结果表明,输出的六角形光束的相对光通量为96%,近似于平顶的能量分布,呈现出了极好的均匀性。 相似文献
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Huber M Grayson M Rother M Biberacher W Wegscheider W Abstreiter G 《Physical review letters》2005,94(1):016805
Momentum-resolved magnetotunneling spectroscopy is performed at a single sharp quantum Hall (QH) edge to probe the structure of integer QH edge modes. An epitaxially overgrown cleaved edge is shown to realize the sharp-edge limit with interchannel distances smaller than both the magnetic length and the Bohr radius where the Chklovskii soft-edge picture is no longer valid. The line shape of principal conductance peaks is explained, and an edge filling factor is determined from the peak position. A step in the dispersion is attributed to fluctuations in the QH ground energy. 相似文献
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Masashi Ohkawa Kazuhiko Hasebe Chikara Nishiwaki Seishi Sekine Takashi Sato 《Optical Review》2000,7(2):144-148
We theoretically and experimentally investigated fundamental characteristics of an integrated optic pressure sensor using intermodal interference between the lowest-order TM-like and TE-like modes. The sensor consists of a rectangular diaphragm and a straight single-mode waveguide along an edge of the diaphragm. Its operation is based on a difference of phase retardations produced in the two guided modes through the photoelastic effect. The sensor was fabricated by bonding two glass substrates together: a Corning 0211 glass 300 μMm thick to form a waveguide and a thick substrate with a 10 mm × 10 mm square hole to define the diaphragm. The fabricated sensor was successfully tested using a He-Ne laser at 633 nm. The halfwave pressure was measured to be 77 kPa which is almost double the theoretical estimate. 相似文献
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Haiyong Zhu Ge Zhang Chenghui Huang Yong Wei Lingxiong Huang Yidong Huang 《Optics Communications》2009,282(4):601-604
An eye-safe, high peak power optical parameter oscillator (OPO) intracavity pumped by electro-optic Q-switched Nd:YAG laser is presented. This OPO is based on a 20 mm length KTiOAsO4 crystal with non-critical phase matching (θ = 90°, ?=0°) cut. An aperture ∅3 mm acted as limiting diaphragm to get good beam quality of pumping laser. The output energy of 25 mJ at the signal wavelength 1.53 μm was obtained with repetition rate of 1 Hz. The highest peak power intensity was up to 88 MW/cm2 with pulse width of 4 ns. Without diaphragm, the maximum output energy of 90 mJ was achieved with area of light spot (∅6 mm) four times larger, but the peak power intensity was lower. 相似文献
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Frequency doubling of spatially limited laser beams in nonlinear crystals is investigated theoretically. It was shown that the major factor, which reduces the second harmonic generation (SHG) efficiency in this case, is a diaphragm aperture effect, caused by influence of extraordinary polarized laser beams. In that case a spatial shift of mutually orthogonally polarized beams of the incident waves relative to each other in perpendicular direction of wave transmission at the entry to crystals lead to increase the efficiency of SHG of limited beams. 相似文献
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Efficient collinear frequency tripling of femtosecond laser with compensation of group velocity delay
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This paper demonstrates an approach that negative uniaxial crystal
has a relative anomalous dispersion effect which can compensate group
velocity delay, and applies this approach to nonlinear frequency
conversion of an ultrafast laser field. High efficiency of the third
harmonic generation is experimentally fulfilled by adopting a
collinear configuration of doubing-compensation-tripling system.
Through finely adjusting the incident angle and optical axis direction
of the compensation plate, it obtains ultraviolet (UV) output energy of
0.32~mJ centered at 270~nm with spectral bandwidth of 2~nm when
input beam at 800~nm was 70~fs pulse duration and 6~mJ pulse energy
which was extracted from Ti:sapphire laser system by a diaphragm,
corresponding to an 800-to-270~nm conversion efficiency of 5.3%
and a factor-of-1.6 improvement in the third harmonic generation of
UV band in comparison with a general conventional configuration.
Furthermore, when the full energy of 18~mJ from a Ti:sapphire laser system
was used and optimized, the UV emission could reach 0.83~mJ. 相似文献
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Optimization of the glass cylindrical active element (AE) of a solid-state laser is carried out. Dependences of the optical
quality of a laser medium on scale-geometry parameters of the AE with different-intensity optical pumping are obtained. The
possibility of considerable increasing of the laser efficiency by using an aperture diaphragm is shown.
Baltic State Technical University, 1, 1st. Krasnoarmeiskaya St., St.-Petersburg, 198005, Russia. Translated from Zhurnal Prikladnoi
Spektroskopii, Vol. 64, No. 6, pp. 734–737, November–December, 1997. 相似文献