共查询到20条相似文献,搜索用时 15 毫秒
1.
We report on a slowing down of light pulses using degenerate backward-wave four-wave mixing in a photorefractive crystal. The delay and width of the output pulse for the amplified transmitted beam and for the phase-conjugated beam are studied as a function of the input pulse width. We demonstrate that the four-wave mixing process ensures a larger slowing down of short pulses compared to the photorefractive two-beam coupling scheme and guarantees the elimination of forerunners, which are among the principal drawbacks for slowing down of short pulses with two-beam coupling. The technique may be extended to slowing down of light with degenerate or nearly degenerate backward-wave four-wave mixing based on other types of nonlinearities. 相似文献
2.
《Superlattices and Microstructures》2001,29(4):301-307
The time-resolved differential absorption of the ZnSe/ZnSTe superlattice is studied using femtosecond pump-probe measurements. Transient spectral hole burning due to the initial nonthermal carrier distribution is observed at zero time delay and the carriers are thermalized within 0.5 ps. The high-energy tail of the differential absorption spectra was used to deduce the effective temperature of the thermalized carriers. Rapid hot-carrier cooling from a temperature of 763 to 450 K within the first 4 ps is observed, with carrier cooling slowing down hence. This initial fast hot-carrier cooling is consistent with the strong carrier–phonon interaction in large gap II–VI semiconductors. 相似文献
3.
The line shape of the 773 keV emission line emitted by187Re depends on the slowing down of the recoil the atom receives in the precedingβ transition. Using the nuclear resonance fluorescence method the line profile was studied for sources where the radioactive atoms are embedded in single crystals of W and WSe2 and in polycrystalline samples of Nb. The experimental results for W and Nb are in complete agreement with predictions by a theory in which the slowing down is calculated starting from a Born-v. Karman lattice model. The temperature dependence of the line shape yields the phonon lifetimes in W and Nb (W) to beτ(300 K)=(2.4±0.3)ps andτ(300 K)=(1.7±0.2) ps, respectively. Measurements for the slowing down of the recoiling atoms perpendicularly to and along the hexagonal axis of WSe2 yielded an anisotropy in qualitative agreement with expected values. 相似文献
4.
5.
《中国光学快报(英文版)》2015,(6)
The characteristics of stimulated Brillouin scattering(SBS) in perfluorinated amine media and the experimental structure used in hundreds of picoseconds pulse compression at 532 nm are demonstrated. A two-stage SBS pulse compression structure is adopted for this work. The compact double-cell SBS compression structure and the scattering media FC-70 are chosen to compress the incident light from 9.5 to about 1 ns in the first stage. Then,the light is used as the pumping source for the second pulse compression. In the second stage, using a single-cell SBS structure in a pulse compression system, perfluorinated amine media with different phonon lifetimes, such as FC-3283, FC-40, FC-43, and FC-70, are chosen to run the comparative experimental study. The narrowest compressed pulse times obtained are 294, 274, 277, and 194 ps; they respectively correspond to the above listed media. The average width of the compressed pulse width is 320 ps for FC-3283, with a fluctuation range of87 ps. For FC-40, the average pulse width is 320 ps, with a fluctuation range of 72 ps. And for FC-43, the average pulse width is 335 ps, with a fluctuation range of 88 ps. However, the average pulse width is only 280 ps for FC-70, with a fluctuation range of 57 ps. The highest energy reflectivity is more than 80% for all of the media. The experimental results show that a two-stage SBS pulse compression system has lower pump energy requirements, thus making it easier to achieve a compressed pulse waveform. The results also show that the shorter the phonon lifetime of the medium, the narrower the obtained compressed pulse width. 相似文献
6.
Light absorption and slowing down when traveling in a medium of four-level atoms with a doublet of close-lying upper levels is studied in conditions of electromagnetically induced transparency (EIT). It is shown that the presence of the second upper level leads to an increase in the absorption of the probe pulse. However, a control-pulse-detuning range exists between the doublet levels where light decelerates considerably more than in the case of ideal EIT. 相似文献
7.
8.
9.
在理论上从四波混频的强度耦合方程出发,给出了基于光纤光参量放大(FOPA)光脉冲的光场表达式,并进一步分析了信号光被相位调制或强度调制后,光脉冲的频率啁啾和强度演化.结论指出:若信号光被强度调制,对所生成脉冲宽度无明显的影响,但可以提高消光比;若信号光被相位调制,所生成的脉冲具有更大的线性正啁啾,可以在相同的抽运功率条件下得到比无相位调制时更窄的脉冲.实验上给出了10 GHz工作速率下的结果,其结果与理论分析符合得很好.通过信号光的相位调制,在05 W平均抽运功率条件下得到了消光比22 dB,脉宽为5
关键词:
光纤参量放大
四波混频
光脉冲源
频率啁啾 相似文献
10.
We have theoretically investigated the main features of pulse deceleration and pulse-shape transformations during phase conjugation
in photorefractive nonlinear media. The main attention in article is paid to the critical features which occur near the threshold
of mirrorless oscillation. It is shown that the effects of critical enhancement when approaching the threshold do not lead
to superior light slowing down characteristics as compared to the case of two-beam coupling. At the same time, essentially
new features of pulse-shape transformation occur above the threshold. 相似文献
11.
The coherent light–matter interaction in a 4-level cascade-type subband system of an asymmetric GaAs/AlGaAs quantum well structure is studied in pump-probe transmission experiments with picosecond (ps) time resolution. Coupling two excited subbands by an intense mid-infrared laser pulse at low sample temperatures is found to result in a substantially increased transparency of the fundamental e1–e2 transition. We find a reduction of the absorption coefficient by ~80%, which is one of the most pronounced electromagnetically induced transparency in solid state systems observed so far. 相似文献
12.
We theoretically investigate slow and fast light propagation and pulse velocity control in a nanocavity containing a single quantum dot side-coupled to a planar-photonic-crystal waveguide. We demonstrate that low coupling strength (i.e., the weak coupling regime) between a cavity and a dot, under on-resonance condition, can lead to delays of about +90 ps for a pulse 1/e-width of 280 ps. The group delay dependence on the various coupling parameters suggests achievable delays of +300 ps and consequently very slow light speeds of around 5000 m/s in a 1.5 microm cavity-waveguide section. We also show that under off-resonant condition one can achieve significant pulse advancement of -60 ps. 相似文献
13.
《Comptes Rendus de l''Academie des Sciences Series IV Physics》2000,1(8):1053-1063
Recent progress using the VULCAN laser at the Rutherford Appleton Laboratory to pump X-ray lasing in nickel-like ions is reviewed. Double pulse pumping with ∼100 ps pulses has been shown to produce significantly greater X-ray laser output than single pulses of duration 0.1–1 ns. With double pulse pumping, the main pumping pulse interacts with a pre-formed plasma created by a pre-pulse. The efficiency of lasing increases as there is a reduced effect of refraction of the X-ray laser beam due to smaller density gradients and larger gain volumes, which enable propagation of the X-ray laser beam along the full length of the target. The record shortest wavelength saturated laser at 5.9 nm has been achieved in Ni-like dysprosium using double pulse pumping of 75 ps duration from the VULCAN laser. A variant of the double pulse pumping using a single ∼100 ps laser pulse and a superimposed short ∼1 ps pulse has been found to further increase the efficiency of lasing by reducing the effects of over-ionisation during the gain period. The record shortest wavelength saturated laser pumped by a short ∼1 ps pulse has been achieved in Ni-like samarium using the VULCAN laser operating in chirped pulse amplified (CPA) mode. Ni-like samarium lases at 7.3 nm. 相似文献
14.
In this paper, we present a theoretical calculation of a highly nonlinear germanium (Ge) doped photonic crystal fiber with all-normal group velocity dispersion to design a supercontinuum (SC) light source at 1.55 μm. By doping 3% higher refractive index Ge inside the host silica, the nonlinear coefficient is increased to a value as large as 60.5 W?1 km?1 at 1.55 μm. A 10 dB bandwidth of a 120 nm SC spectrum for a 2.5 ps input optical pulse and a 10 dB bandwidth of a 190 nm SC spectrum for a 1.0 ps input optical pulse have been found using the same fiber length of 200m and input optical power of 18 W. The coherent lengths of the generated SC light sources are found to be 8.8 μm for a 2.5 ps input optical pulse and 5.6 μm for a 1.0 ps input optical pulse. Therefore, the highest longitudinal resolution at 1.55 μm is found to be about 4.0 μm for biological tissues. 相似文献
15.
Synchronized signal (650 ps) and pump (1.3 ns) pulses were generated using 4-pass geometry in a grating pair based pulse stretcher
unit. The pump pulse has been further amplified in a high gain regenerative amplifier. This amplified pulse was used as the
pump in an optical parametric chirped pulse amplification based Nd:glass laser system. As the chirped signal pulse and the
pump pulse originated from the same oscillator, the time jitter between the pump pulse and the signal pulse can be <50 ps. 相似文献
16.
与通常利用二阶强度关联测量实现时域鬼成像不同,本文利用时域热光源借助干涉仪通过一阶关联实现时域成像.基于空域光束的近轴衍射和时域窄带脉冲在色散介质中色散之间的空间-时间二象性,在时域脉冲响应函数的基础上得到了表征一阶关联时域成像的强度表达式,分析研究了光源脉冲宽度和相干时间对成像可见度和分辨率的影响.结果一方面表明基于热光场一阶关联的时域成像在不需要额外色散补偿或消除条件下可以实现时域物体信号的再现,另一方面表明当光源脉冲宽度一定时,成像可见度随光源脉冲相干时间的增加而增加,但是成像分辨率逐渐降低,其中当光源脉冲宽度约为100 ps,相干时间约为0.5 ps时,间隔为20 ps,宽度为8 ps的时域矩形波型物体的成像质量(兼顾可见度和分辨率)较好.该结果对于基于热光一阶关联的时域成像在时序信号测量中的应用具有重要意义. 相似文献
17.
18.
Baumgartl M Jansen F Stutzki F Jauregui C Ortaç B Limpert J Tünnermann A 《Optics letters》2011,36(2):244-246
We report on the generation of high-average-power and high-peak-power ultrashort pulses from a mode-locked fiber laser operating in the all-normal-dispersion regime. As gain medium, a large-mode-area ytterbium-doped large-pitch photonic-crystal fiber is used. The self-starting fiber laser delivers 27 W of average power at 50.57 MHz repetition rate, resulting in 534 nJ of pulse energy. The laser produces positively chirped 2 ps output pulses, which are compressed down to sub-100 fs, leading to pulse peak powers as high as 3.2 MW. 相似文献
19.
Slow light in photonic crystals 总被引:3,自引:0,他引:3
The problem of slowing down light by orders of magnitude has been extensively discussed in the literature. Such a possibility can be useful in a variety of optical and microwave applications. Many qualitatively different approaches have been explored. Here we discuss how this goal can be achieved in linear dispersive media, such as photonic crystals. The existence of slowly propagating electromagnetic waves in photonic crystals is quite obvious and well known. The main problem, though, has been how to convert the input radiation into the slow mode without losing a significant portion of the incident light energy to absorption, reflection, etc. We show that the so-called frozen mode regime offers a unique solution to the above problem. Under the frozen mode regime, the incident light enters the photonic crystal with little reflection and, subsequently, is completely converted into the frozen mode with huge amplitude and almost zero group velocity. The linearity of the above effect allows the slowing of light regardless of its intensity. An additional advantage of photonic crystals over other methods of slowing down light is that photonic crystals can preserve both time and space coherence of the input electromagnetic wave. 相似文献
20.
We propose a scheme for slowing down decay into a continuum. We make use of a sequence of ultrashort 2pi pulses applied on an auxiliary transition of the system so that there is a destructive interference between the two transition amplitudes--one before the application of the pulse and the other after the application of the pulse. We give explicit results for a structured continuum. Our scheme can also inhibit unwanted transitions. 相似文献