共查询到20条相似文献,搜索用时 0 毫秒
1.
S. Yu. Ketkov H. L. Selzle E. W. Schlag S. N. Titova L. V. Kalakutskaya 《Optics and Spectroscopy》2004,97(4):567-571
Two-color photoionization of nickelocene molecules cooled in a supersonic jet is performed using a tunable nanosecond pulsed laser. The first stage of the multiphoton excitation is the transition from the highest occupied molecular orbital of nickelocene to the lowest Rydberg level. Conditions are found under which molecular ions (η 5-C5H5)2Ni+ are the only product of the multiphoton ionization in the one-color experiment. Irradiation of an excited molecule by an intense pulse of another laser increases significantly the yield of molecular ions. The dependence of the yield of (η5-C5H5)2Ni+ ions on the frequency of the second laser makes it possible to determine the adiabatic ionization potential of nickelocene as 6.138±0.012eV. 相似文献
2.
《Journal of Electron Spectroscopy and Related Phenomena》2005,142(3):179-192
Recent developments of two-color infrared (IR)-vacuum ultraviolet (VUV) and VUV-IR photoionization and photoelectron detection schemes for spectroscopic studies are described. By preparing molecules in selected rovibrational states by IR excitation prior to VUV-photoionization, state-selected and state-to-state photoionization cross sections can be obtained by IR-VUV-photoionization efficiency (IR-VUV-PIE) and IR-VUV-pulsed field ionization-photoelectron (IR-VUV-PFI-PE) measurements, respectively. Rotationally resolved autoionizing Rydberg states converging to excited ionic states, which cannot be observed by single-photon VUV-PIE measurements, can be examined by the IR-VUV-PIE scheme. By monitoring the photoion and the PFI-PE intensities at a fixed VUV energy as a function of IR frequency, the respective IR photoion and IR absorption spectra of the corresponding neutral molecule can be measured. Two-color VUV-IR photo-induced Rydberg ionization (PIRI) experiment, in which high-n Rydberg states are prepared by VUV-photoexcitation followed by IR-induced autoionization, has also been demonstrated. Since the IR-VUV-PIE, IR-VUV-PFI-PE, and VUV-IR-PIRI methods do not require the existence of a bound intermediate electronic state in the UV and are generally applicable to all molecules, the development of these two-color photoionization and photoelectron schemes is expected to significantly enhance the scope of VUV spectroscopy and chemistry. 相似文献
3.
U. Brinkmann W. Hartig H. Telle H. Walther 《Applied Physics A: Materials Science & Processing》1974,5(2):109-115
The isotope specific two-step photoionization of metastable Ca atoms was investigated using a continuous wave dye laser and
an Ar+ laser. The photoionization was performed via a transition to an autoionizing state. Therefore an ionization probability as
high as 10−2 could be obtained. 相似文献
4.
Vas Dev M. L. Shah A. K. Pulhani B. M. Suri 《Applied physics. B, Lasers and optics》2005,80(4-5):587-594
A U–Ne hollow cathode discharge tube is used as a source of uranium atomic vapors as well as a photoelectron/photoion detector
for carrying out two-color three-photon photoionization spectroscopy of uranium. Using the uranium excitation transition 0
cm−1 (5L
6
0
) → 16 900.38 cm−1 (7M7) at 591.5-nm laser wavelength as a first step transition and scanning the wavelength of a second laser from 558 to 568 nm,
high-lying odd-parity atomic levels of uranium are studied in the energy region 34 500–34 813 cm−1. All the expected 21 odd-parity atomic levels identified by various researchers in this region are observed in a single spectrum,
demonstrating the high sensitivity achieved therein. In addition to this, we have identified eight autoionization resonances
of uranium starting from its odd-parity atomic level at 33 801.06 cm−1 pumped by two-photon excitation. Four out of these eight autoionization resonances are observed for the first time. 相似文献
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为了满足数字摄像法能见度测量仪均匀光源的要求,提高半导体发光二极管照明的均匀性,该文提出一种基于数字图像分析技术的设计方法。首先测量单颗LED在模组区域的亮度分布,进而拟合分布函数,再运用多颗LED亮度叠加原理,计算出不均匀度最小的多颗LED阵列方式,或固定均匀度对应的最佳尺寸。对仿真数据和实测数据进行对比分析,结果表明,该文计算出的LED阵列方式,与单边阵列相比,均匀度显著提高,最高可达95%以上。 相似文献
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A. Johansson M.K. Raarup Z.S. Li V. Lokhnygin D. Descamps C. Lyngå E. Mevel J. Larsson C.-G. Wahlström S. Aloise M. Gisselbrecht M. Meyer A. L'Huillier 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2003,22(1):3-11
A pump-probe technique has been applied for measuring the lifetimes and absolute photoionization cross-sections of excited
He states. The 1s2p 1P and 1s3p 1P states of He are excited by using the 13th and the 14th harmonic, respectively, of a tunable 70 ps dye laser generated in
a Kr gas jet. The states are ionized after a varying time delay, by absorption of probe photons with energies between 1.6
and 4.5 eV. Lifetimes of τ(1s2p) = 0.57 ns and τ(1s3p) = 1.76 ns are determined with a precision of about 15%. A significant enhancement of the number of ions present in the lifetime
curves at zero time delay for pressures above 6×10-5 mbar is attributed to direct two-photon ionization of He in combination with AC Stark broadening of the excited state and
absorption of the XUV light in the medium. Absolute photoionization cross-sections from the He 1s2p 1P and He 1s3p 1P states in the threshold region are determined by measuring the saturation of the ionization process with a precision of
∼ 25%. In addition, the variation of the relative orientation between the polarization vectors of the pump and probe beams
enables the determination of partial photoionization cross-sections.
Received 3 June 2002 / Received in final form 14 August 2002 Published online 22 October 2002
RID="a"
ID="a"Present address: Department of Biophysics, Leiden University, 2333 CA Leiden, The Netherlands.
RID="b"
ID="b"Present address: Continuum Electro-Optics Inc., 3150 Central Expressway, Santa Clara, CA 95051, USA.
RID="c"
ID="c"Present address: CEA/DRECAM/SPAM, CEN Saclay, 91105 Gif-sur-Yvette, France.
RID="d"
ID="d"Present address: Department of Physics, National University of Rwanda, Butare, Rwanda.
RID="e"
ID="e"Present address: CELIA, Université Bordeaux 1, 33405 Talence, France.
RID="f"
ID="f"Present address: MAX-Lab, Lund University, Box 118, 221 00 Lund, Sweden.
RID="g"
ID="g"e-mail: anne.lhuillier@fysik.lth.se 相似文献
9.
Optimized 481 Mb/s visible light communication system using phosphorescent white LED 总被引:3,自引:2,他引:1
We demonstrate a visible light communication system based on DC-biased optical orthogonal frequency-division multiplexing(DCO-OFDM) and achieve a bit rate of 481 Mb/s at a communication distance of 65 cm by employing single 1 W commercial phosphorescent light-emitting diode(LED). The average bit error rate of the received data is 2.3×10-3, which is below the forward error correction limit, 3.8×10-3. The effect of signal clipping in DCO-OFDM system is studied and resource allocation algorithms are utilized. At least 13% capacity improvement can be obtained by suitable signal clipping and resource allocation. 相似文献
10.
V. Schmidt 《Physics letters. A》1973,45(1):63-64
The angular distribution of photoelectrons after photoionization by elliptically polarized light is derived. 相似文献
11.
Jahnke T Foucar L Titze J Wallauer R Osipov T Benis EP Alnaser A Jagutzki O Arnold W Semenov SK Cherepkov NA Schmidt LP Czasch A Staudte A Schöffler M Cocke CL Prior MH Schmidt-Böcking H Dörner R 《Physical review letters》2004,93(8):083002
Diffraction of a low energy (<4 eV) carbon-K-photoelectron wave that is created inside a CO molecule by absorption of a circularly polarized photon is investigated. The measurements resolve the vibrational states of the K-shell ionized CO+ molecule and display the photoelectron diffraction patterns in the molecular frame. These show significant variation for the different vibrational states. This effect is stronger than predicted by state-of-the-art theory. As this study is performed close to C-K-threshold and, therefore, far below the molecule's sigma-shape resonance, this surprisingly strong effect is not related to that resonance phenomenon. 相似文献
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针对LED光谱分布可调光源对LED寿命以及光谱一致性的要求,对可见光和近红外波段的29种LED分别进行200 h的电流加速老化试验,并提出LED光谱一致性筛选算法。老化试验结果表明:峰值波长为385 nm、400 nm 和420 1 nm 3种LED的辐射通量平均衰减分别为24.8 %、10.7 %和25.6 %,不能用于LED光谱分布可调光源;剩余的26种LED的辐射通量平均衰减量均低于3.5 %,可作为光谱分布可调光源的内部光源。LED光谱一致性筛选算法以LED光谱数据为基础,计算同类LED间的相对光谱偏差,26种LED的相对光谱偏差均小于4.5 %,保证了所筛选出LED的光谱一致性。 相似文献
14.
天幕灯是一款用于近距离照射大面积幕布的特殊灯具。为了在限定的区域内获得幕布的均匀照明,天幕灯需实现非对称、大角度的特定出射光强分布。基于几何光学和辐照度理论,首先建立满足幕布均匀照明要求的天幕灯配光曲线模型,然后再根据LED光源的发光特性进行二次光学设计,使LED天幕灯的出射光强分布与所需的配光曲线模型相匹配。根据能量守恒定律将配光曲线模型进行均匀离散化处理,建立直射和反射的有效叠加和补偿,依此设计得到反射面面型,实现照明要求。通过Zemax对所设计的LED天幕灯进行模拟仿真,结果表明,满足配光曲线的LED天幕灯可以通过多个灯具的简单照明叠加实现在近距离范围内对不同大小和形状的幕布进行均匀照明,其照明均匀度可达到85%以上,能量利用率可达到80%以上。 相似文献
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The fluorescence emission from indole resulting from two-color two-photon (2C2P) excitation with 400 and 800 nm wavelengths is observed, using the second harmonic and fundamental wavelength of a 800 nm 40 fs pulsed Ti:Sapphire femtosecond (fs) regenerative amplifier operating at a repetition rate of 1 kHz. By delaying one fs laser pulse relative to the other, the cross correlation of fluorescence is observed, which indicates the generation of 2C2P fluorescence signal in the experiment. The strongest 2C2P fluorescence emission characterized by the peak of cross correlation curve suggests optimal temporal overlap of the two fs laser pulses. The 2C2P fluorescence signal is linearly dependent on the total excitation intensity. The fluorescence signals with 400 nm and 800 nm irradiation alone are also demonstrated and discussed in this paper. 相似文献
17.
用高亮度LED和简便数据处理方法测定椭圆偏振光的椭圆曲线 总被引:1,自引:0,他引:1
通过建立椭圆偏振光在β方向上的光振动大小与检偏器在β+90°方向时光电检测器所测光强之间的关系式,以高亮度LED为光源,可简便地测定椭圆偏振光的椭圆曲线. 相似文献
18.
Pei Ding Li Shao Junqiao Wang Yan Li Fanguang Zeng Erjun Liang 《Optical and Quantum Electronics》2017,49(5):194
High conversion efficiency and quantum efficiency is essential for the phosphor in an efficient phosphor-based white light LEDs. Here, based on the coherent harmonic and the random independent emitter model, we demonstrate theoretically that the silicon nanoantenna array can dramatically enhance the output power of emitters in a phosphor layer by investigating the far-field radiation enhancement of an electric dipole assisted by silicon nanopillars in a waveguide structure. Compared with the plasmonic silver nanoantenna array, the silicon nanoantenna array can increase the enhancement factor of light extraction efficiency (LEE) over 50% for the dipole source at the wavelength of 620 nm, thus showing potential applications in white light LEDs. The enhanced LEE is ascribed to the low-loss directional light scattering of silicon nanoantennas and the strong guided mode resonances caused by their array. The calculation results also indicate that the far-field radiation can be tailored significantly by changing the aspect ratio of silicon nanopillars while presenting a good directivity. Our research is expected to give more insights into the design and optimization of the solid-state lighting, gaining and lasing systems by integrating silicon-based nanoantennas. 相似文献
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20.
Sheng-Han Tu Jui-Wen Pan Chih-Ming Wang Yeeu-Chang Lee Jenq-Yang Chang 《Optical Review》2009,16(3):318-322
Light emitting diodes (LEDs) have numerous advantages as light sources in projectors. LEDs are more compact, exhibit a larger
color gamut, have a longer lifetime, and need a lower supply voltage. However, there is still one important disadvantage:
the optical power per unit of étendue (luminance) of an LED is significantly low. As a result of the étendue limitations of
LEDs, the projected flux on the screen will not be high. Despite this shortcoming, LED’s are still of great interest for low
power applications because of their other superior properties. Thus we collect the available light flux optimally and combine
multiple high luminance LEDs within the system. In this study we discuss three collection systems designed to collect the
LED flux with high optical efficiency while retaining small device size. The best collection efficiency attained with our
collection systems is 96%. The fabrication tolerance and cost of our collection systems are also analyzed. 相似文献