共查询到20条相似文献,搜索用时 31 毫秒
1.
Yanjie Zhang Zifeng Lu Xuefeng Deng Yichun Liu Yingying Zhao 《Optics Communications》2003,220(4-6):289-295
Holographic gratings were optically recorded by two beams from a He–Ne laser operating at 632.8 nm in poly (methyl methacrylate) (PMMA) film containing push–pull azo dye. The holographic characteristics of the recorded gratings were dependent on the polarization direction of the recording beams and the relationship between the diffractive signals and the power density of recording beams was investigated. The formation of holographic gratings accompanied by 532 nm (double-frequency of Nd:YAG laser) irradiation was studied in detail. It was found that the effect of 532 nm laser to the holographic grating lay in two aspects. The acceleration effect of 532 nm laser to the formation of holographic grating is predominant when the power density of 532 nm laser is low. While at relatively high power density of 532 nm laser, the erasure is the main factor to the holographic grating. Moreover, the holographic grating was probed by 532 nm laser at low power density and the dependence of the first order diffractive signal on the recording beam power density was also presented. 相似文献
2.
The signal of heterodyne-detected electrostrictive laser-induced gratings (LIGs) originates from the interference of a reference laser beam with the laser light diffracted at the counterpropagating sound-wave packets, which are generated in the overlap volume of crossed laser beams. The frequencies of the sound waves, which contain the information on the sound velocity and on the motion of the medium, can approximately be extracted from the frequencies at the maxima of the two peaks, which dominate the power spectrum of the heterodyne LIG signal intensity. In free-air jets behind a slot nozzle, flow velocities up to 60 ms-1 were determined by quick fits from the power spectrum and by fitting the time-dependent signal intensity data to model functions. Results agree well, the standard deviations being about one-half in the latter case (1.6–2.6 ms-1, for positions close to the nozzle). Problems arising from the sampling and from the finite observation time of the signal intensity are discussed. Furthermore, the results of the LIG measurements were compared with data provided by laser Doppler anemometry. As an application of the instantaneous and unseeded LIG measurement technique, temperatures in heated air jets were determined simultaneously with the flow velocity by quick fits from the power spectrum. PACS 42.62.-b; 47.62.+q; 43.58.+z 相似文献
3.
K?stutis Regelskis Gediminas Ra?iukaitis Mindaugas Gedvilas 《Applied Surface Science》2007,253(15):6584-6587
The beam of a nanosecond pulse laser tightly focused to a line was applied for the back-side ablation of the chromium thin film on a glass substrate. The stripe ablated with a single laser pulse had sharp edges on both sides and ridges of the melted metal around it. The partially overlapping pulses formed a wide cleaned area with a complicated structure made of the metal remaining from the ridges. Regular structures, ripples, were developed when laser fluence was slightly above the single-pulse removal threshold and the shift between pulses was less than half width of the line ablated with a single laser pulse. The ripples were located periodically (∼4 μm) and were orientated perpendicularly to the long axis of the beam spot. Their orientation did not depend on the laser beam polarization. Different models of the ripple formation in the thin metal film were considered, and instability of the moving vapor-liquid-solid contact line during evaporation of thin liquid films appears to be the most probable process responsible for the observed phenomena. Formation of regular gratings with the unlimited line length was experimentally implemented by using the above-mentioned technique. 相似文献
4.
体光栅光谱组束是获得高功率激光输出的一种有效途径.在有限的可用带宽内,光谱通道间隔影响着组束光束数目以及最终的高功率组束输出.采用耦合波理论,建立了一个两通道高功率光谱组束模型.通过优化体光栅光谱通道间隔,可放宽对组束子束线宽和功率的限制,组束功率可大幅提升而光谱密度并无显著下降.基于此,实验上获得了2.5 kW组束输出,绝对效率超过85%,通道间隔5 nm,光谱密度为0.51kW/nm.组束功率1 kW时,组束输出能保持好的光束质量;组束功率1.5kW时光束质量恶化较明显,通过分析发现,组束光束质量的恶化主要受限于体光栅的色散及高功率下体光栅复杂的热畸变. 相似文献
5.
建立了分别用一个和两个反射式体布拉格光栅实现两路和三路光束合成的物理模型,模型中考虑了体布拉格光栅的吸收,并假设入射光束的光谱具有高斯线型。通过对两路和三路光谱合成的数值分析可知:当光谱宽度为0.1 nm时,两路和三路光谱合成的效率分别为98.76%和97.69%;当光谱宽度为0.3 nm的时候,对应的效率分别为97.34%和95.78%。随着光谱宽度的增加,合成的效率明显降低。当光谱宽度较窄时,实现多路光束较高的合成效率是可行的,这为高能激光的获得提供了一种确实可行的方法。 相似文献
6.
W. Holzer A. Penzkofer T. Pertsch N. Danz A. Bräuer E.B. Kley H. Tillmann C. Bader H.-H. Hörhold 《Applied physics. B, Lasers and optics》2002,74(4-5):333-342
Wave-guided thin-film distributed-feedback (DFB) polymer lasers are fabricated by spin coating a PPV-derived semiconducting
polymer, thianthrene-DOO-PPV, onto oxidised silicon wafers with corrugated second-order periodic gratings. The gratings are
written by reactive ion beam etching. Laser action is achieved by transverse pumping with picosecond laser pulses (wavelength
347.15 nm, duration 35 ps). The DFB-laser surface emission and edge emission are analysed. Outside the grating region the
polymer film is used for comparative wave-guided travelling wave laser (amplified spontaneous emission (ASE)) studies. The
pump pulse threshold energy density for wave-guided DFB-laser action (4–9 μJ cm-2) is found to be approximately a factor of two lower than the threshold for wave-guided travelling wave laser action. The
spectral width of the DFB laser (down to ΔλDFB≈0.07 nm) is considerably narrower than that of the travelling wave laser (ΔλTWL≈14 nm). The DFB-laser emission is highly linearly polarised transverse to the grating axis (TE mode). Only at high pump pulse
energy densities does an additional weak TM mode build up. The surface-emitted DFB-laser radiation has a low divergence along
the grating direction. For both the DFB lasers and the travelling wave lasers, gain saturation occurs at high excitation energy
densities.
Received: 7 January 2002 / Revised version: 15 February 2002 / Published online: 14 March 2002 相似文献
7.
The kinetics of anisotropic scattering and optical turbulence upon formation of quasi-periodic structures (QPSs) in photosensitive composite AgCl:Ag films irradiated by Gaussian beams of a He-Ne laser is studied. The buildup kinetics of the scattering induced by an unfocused beam is used to find the threshold exposures for the formation of QPSs and an additional spatiotemporal instability resulting from interaction between the gratings during their development. It was established that there exists a threshold for the formation of a strong instability (optical turbulence) when the QPSs are induced by a focused beam. The decay curves of the mean frequency of the chaotic intensity oscillations, as well as the dependence of this frequency on the beam power, are obtained under conditions of turbulence. It is shown that both the turbulence and its decay are controlled by a competition between the microgratings in the QPSs and by gradual widening of the area of active competition under the action of the Gaussian beam. The AgCl:Ag films are shown to be capable of rapidly and repeatedly rearranging the QPSs and the spatial orientation of the anisotropic scattering upon variation of the direction of linear polarization of the laser beam. 相似文献
8.
C. O'Neill B. Coulombe P. Galarneau M.-M. Denariez-Roberge 《Applied physics. B, Lasers and optics》1990,51(2):116-120
Nondegenerate four-wave mixing has been performed in DDI-methanol solutions using ruby laser as writing beams. The reading beam was either a pulsed one at 538.8 nm or a continuous one at 632.8 nm. Contributions from both saturation and thermal gratings were separated temporally and evaluated. 相似文献
9.
Juha?M.?Saarela Torbj?rn?L?fqvist Kerstin?Ramser Per?Gren Erik?Olson Jan?Niemi Mikael?Sj?dahl 《Central European Journal of Physics》2010,8(2):235-241
This study is focused on exploring the feasibility of an all-optic surface scanning method in determining the size and position
of a submerged, laser generated, optoacoustic (OA) source. The optoacoustic effect in this case was generated when the absorption
of a short electromagnetic pulse in matter caused a dielectric breakdown, a plasma emission flash and a subsequent acoustic
wave. In the experiment, a laser pulse with λ = 1064 nm and 12 ns pulse length was aimed at a volume of deionized water. When
the laser beam was focused by a f = 16 mm lens, a single dielectric breakdown spot occurred. When a f = 40 mm was used several breakdowns in a row were induced. The breakdowns were photographed using a double shutter camera.
The acoustic wave generated by the dielectric breakdowns were detected at a point on the water surface using a laser Doppler
vibrometer (LDV). First, the LDV signal was used to calculate the speed of sound with an accuracy of 10 m/s. Secondly, the
location and length of the dielectric breakdown was calculated with an accuracy of 1 mm. The calculated position matched the
breakdown location recorded by a camera. The results show that it is possible to use LDV surface measurements from a single
spot to determine both the position and length of the OA source as well as the speed of sound in the medium. Furthermore,
the LDV measurements also show a secondary peak that originates from the OA source. To unravel the origin and properties of
this interesting feature, further investigations are necessary 相似文献
10.
利用厚体布拉格光栅的波长选择特性对目标光场进行窄带滤波,是实现高光谱成像的一种新途径。基于严格耦合波理论,设计了体布拉格光栅结构,探索了厚体布拉格光栅的制作工艺,搭建系统光路验证了体布拉格光栅的光谱成像能力。研究结果表明:要获得较窄滤波谱宽,需要提高体布拉格光栅的厚度周期比,并严格控制入射光束发散角;刻写光束质量、震动和偏振会极大地影响制作的光栅条纹面质量,需要从优化写入光的光束均匀性、采用防震措施以及调整两刻写光束偏振一致性等方面优化刻写过程,以提高光栅的衍射效率和质量;验证了体布拉格光栅滤波片进行空间二维面阵成像的能力,宽谱光源透射条件下,通过对入射光束进行准直,滤波谱宽5 nm左右,空间分辨率约4 lines/mm;漫反射条件下,使用体布拉格光栅对进行色散补偿,能够实现较为清晰的成像,空间分辨率约4.9 lines/mm。 相似文献
11.
Coherent anti-Stokes Raman scattering (CARS) and normal anti-Stokes Raman scattering (NARS) have been measured in (001) GaP at room temperature due to the 403 cm−1 LO phonons using a continuous wave (CW) 785.0 nm fixed-wavelength pump laser and a CW Stokes laser tunable in the 800-830 nm wavelength range. CARS measurements are normally made using pulsed lasers. The use of CW diode lasers allows a more accurate comparison between the measured and calculated values of the CARS signal. The pump and Stokes laser beams were linearly polarized perpendicular to each other, same as the pump and normal Stokes/anti-Stokes scattered light for the GaP sample used in this work. The pump and Stokes laser powers incident upon the GaP sample, located in the focal plane of a 20 mm effective focal length lens, were <20 and 50 mW, respectively. The diameter of the laser beams in the focal plane of the focusing lens was determined to 40±5 μm. The pump and Stokes laser beam intensities incident upon the 0.3 mm thick GaP sample were <2 and 5 kW cm2, respectively. The powers of the CARS and NARS signals were measured using a Raman spectrometer. The signal output of the Raman spectrometer was calibrated using the pump laser and several neutral density filters. The Raman linewidth (full-width at half-maximum) of the LO phonons was determined to be 0.95±0.05 cm−1, using the variation of the CARS signal with the wavelength of the Stokes laser. The measured powers of the CARS and NARS signals are about a factor of 5 and 1.5, respectively, smaller than those calculated from the corresponding theoretical expressions. 相似文献
12.
We theoretically derive the electric field distribution of an astigmatic Gaussian laser beam after it is focused through a high-aperture objective. We show that astigmatism values that are hard to detect in the collimated laser beam can have a large effect after diffraction-limited focusing. Such astigmatic beams may be frequently encountered in fluorescence correlation measurements and in laser-scanning confocal microscopy. We present experimental measurements of the excitation intensity distribution measured by 3D scanning of single fluorescent molecules immobilized on a glass surface. 相似文献
13.
A 4.8-W M^2 = 4.6 Continuous-Wave Intracavity Sum-Frequency Diode-Pumped Solid-State Yellow Laser 总被引:1,自引:0,他引:1 下载免费PDF全文
A yellow continuous wave with beam quality M^2= 4.6 and output power of 4.8 W at 589nm is generated by intracavity sum-frequency mixing of 1064 nm and 1319 nm radiations of a Nd:YAG laser. To achieve high beam quality at high power, thermally near-unstable flat-flat resonators with two-rod birefringence compensation are designed to obtain the large fundamental mode size inside the Nd:YAG rods and the same beam width inside the KTP crystal. The optimal intracavity power ratio of both 1064nm and 1319nm beams is also considered. The output power fluctuation of the yellow laser remains less than 5% in four hours. 相似文献
14.
15.
The possibility of achieving multikilowatt laser radiation by spectrally combining beams using volume Bragg gratings (VBGs) is shown. The VBGs recorded in a photothermorefractive glass exhibit long-term stability of all its parameters in high-power laser beams with power density >1 MW/cm2 in the cw beam of total power on a kilowatt level. We consider an architecture-specific beam-combining scheme and address the cross-talk minimization problem based on optimal channel positioning. Five-channel high efficiency spectral beam combining resulted in a >750 W near-diffraction-limited cw beam has been demonstrated experimentally. 相似文献
16.
T. Mocek B. Rus M. Kozlová J. Polan P. Homer K. Jakubczak M. Stupka D. Snopek J. Nejdl M. H. Edwards D. S. Whittaker G. J. Tallents P. Mistry G. J. Pert N. Booth Z. Zhai M. Fajardo P. Zeitoun J. Chalupsky V. Hájková L. Juha 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2009,54(2):439-444
An overview of recent advances in applications of currently the most energetic X-ray laser at 21 nm is given. The unique parameters
of this half-cavity based X-ray laser such as record output energy of 10 mJ, highly symmetric beam, robustness and reproducibility,
have made it possible to carry out a number of multidisciplinary scientific projects featuring novel applications of intense
coherent X-ray radiation. Selected results obtained in these experiments are reviewed, including X-ray laser probing of dense
plasmas, measurements of transmission of focused soft X-ray radiation at intensities of up to 1012 W cm-2, measurements of infrared laser ablation rates of thin foils, and ablative microstructuring of solids. 相似文献
17.
研究了激发光增强时其对荧光关联谱(FCS)测量的影响. 强激发光产生的饱和激发会改 变激光诱导荧光的空间分布函数,从而影响FCS的测量结果. 首先根据饱和吸收的物理模型,推导出强激发光情况下有效探测区域变化的定量公式,获得了FCS测量所得到的粒子数和扩散时间与饱和激发光强和激光光强的函数关系,并用于消除饱和吸收造成的系统误差.采用Monte-Carlo模拟方法和实验,对理论分析结果进行了验证. 这将有助于完善FCS分析方法的理论模型,为高激发光强度下的FCS探测提供依据.
关键词:
荧光关联谱
饱和激发
Monte-Carlo模拟 相似文献
18.
G. N. Makarov 《Journal of Experimental and Theoretical Physics》2001,93(6):1222-1230
A method for obtaining an intense secondary pulsed molecular beam is described. The kinetic energy of molecules in the beam can be controlled by vibrational excitation of the molecules in the source under high-power IR laser radiation. A compression shock (shock wave) is used as a source of secondary beams. The shock wave is formed in interaction between an intense pulsed supersonic molecular beam (or flow) and a solid surface. The characteristics of the secondary beam were studied. Its intensity and the degree of gas cooling in it were comparable with the corresponding characteristics of the unperturbed primary beam. Vibrational excitation of molecules in the shock wave and subsequent vibrational-translational relaxation, which occurs when a gas is expanded in a vacuum, allow the kinetic energy of molecules in the secondary beam to be substantially increased. Intense [≥1020 molecules/(sr s)] beams of SF6 and CF3I molecules with kinetic energies approximately equal to 1.5 and 1.2 eV, respectively, were generated in the absence of carrier gases, and SF6 molecular beams with kinetic energies approximately equal to 2.5 and 2.7 eV with He (SF6/He=1/10) and H2 (SF6/H2=1/10) as carrier gases, respectively, were obtained. The spectral and energy characteristics of acceleration of SF6 molecules in the secondary beams were studied. The optimal conditions were found for obtaining high-energy molecules. The possibility of accelerating radicals in secondary molecular beams was demonstrated. 相似文献
19.
报道了一台800 Hz,6.2 W外腔和频的589 nm黄光激光器。基频激光器均采用双棒串接平平对称腔,增益介质为Nd:YAG晶体,采用声光调Q方式分别获得11.1 W的1 064 nm激光和12.6 W的1 319 nm激光。和频晶体采用三硼酸锂(LBO),尺寸为4 mm×4 mm×30 mm,采用Ⅰ类非临界相位匹配。将两束激光通过分光镜合束,聚集后注入LBO晶体,获得589 nm黄光最大输出功率为6.2 W,脉宽为50 ns,和频效率26.2%。x方向和y方向的光束质量平方因子分别为3.20和3.61。 相似文献
20.
The generation of spontaneous (noise) gratings during the simultaneous formation of a holographic grating in thin (on the
order of the cutoff thickness of the TE0 waveguide mode) AgCl-Ag films by two laser beams with λ = 532 nm and polarization vectors that make an angle of 45° with
the plane of incidence have been studied. The electron microscopy images and diffraction patterns have revealed a significant
difference of the spontaneous-grating structure from the structure obtained under irradiation by one laser beam. The spontaneous
gratings have a significant spread in the directions of their wave vector, and the diffraction pattern (recorded using a probe
beam with λ = 337 nm) has the form of a bundle of diverging arcs that intersect at one point. This difference is caused by
self-diffraction from the holographic grating, which is responsible for the main diffraction peaks with odd orders, the growth
of spontaneous gratings because of the interference of the beams diffracted by the holographic grating with the waveguide
TE0 modes scattered in the film, and silver transport to the interference minima. The diffraction patterns are quantitatively
analyzed and the period of the new (formed under two-beam irradiation) spontaneous gratings is calculated. The calculation
results are in good agreement with the experimental data. 相似文献