共查询到20条相似文献,搜索用时 15 毫秒
1.
The possibilities of a recently proposed (Opt. Express 17, 9323 (2009)) method for generating terahertz surface plasmons on
a microstructured (comb-shaped) metal surface using a nonlinear polarization pulse that moves with a superluminal velocity
and is induced by an ultrashort laser pulse in a strip of electrooptic material deposited on the surface are theoretically
studied. For an arbitrary direction of motion of the nonlinear source along the comb-shaped surface, fields of excited terahertz
plasmons and the angular spectral distribution of the radiated energy are calculated. It is shown that the spectral and energy
characteristics of plasmons can be efficiently controlled by varying the direction of motion of the source. Conditions (parameters
of the comb-shaped structure, direction and velocity of motion of the source) that ensure the maximal efficiency of the optical-to-terahertz
conversion are found. The developed method of terahertz generation is promising for surface terahertz spectroscopy. 相似文献
2.
We report the generation of 30 microJ single-cycle terahertz pulses at 100 Hz repetition rate by phase-matched optical rectification in lithium niobate using 28 mJ femtosecond laser pulses. The phase-matching condition is achieved by tilting the laser pulse intensity front. Temporal, spectral, and propagation properties of the generated terahertz pulses are presented. In addition, we discuss possibilities for further increasing the energy of single-cycle terahertz pulses obtained by optical rectification. 相似文献
3.
Generation of terahertz radiation during reflection of femtosecond laser pulses from a metal surface
V. A. Mironov I. V. Oladyshkin E. V. Suvorov D. A. Fadeev 《Journal of Experimental and Theoretical Physics》2014,119(2):179-195
The features of terahertz radiation generated upon oblique incidence of a femtosecond laser pulse on a metal surface are investigated theoretically. We propose a Cherenkov-type generation mechanism associated with excitation of low-frequency surface currents by a p-polarized optical field. The nonlinear surface currents and corresponding electrodynamic characteristics of low-frequency radiation are calculated analytically and by numerical simulation using the hydrodynamic model. The features of Cherenkov generation of terahertz radiation are analyzed, and techniques are proposed for increasing efficiency. 相似文献
4.
We systematically study the optimization of highly efficient terahertz(THz) generation in lithium niobate(LN)crystal pumped by 800 nm laser pulses with 30 fs pulse duration. At room temperature, we obtain a record optical-to-THz energy conversion efficiency of 0.43% by chirping the pump laser pulses. Our method provides a new technique for producing millijoule THz radiation in LN via optical rectification driven by joule-level Ti:sapphire laser systems, which deliver sub-50-fs pulse durations. 相似文献
5.
A. N. Bugai S. V. Sazonov 《Bulletin of the Russian Academy of Sciences: Physics》2009,73(12):1581-1585
A theoretical model is proposed for terahertz radiation generation by femtosecond laser pulses with tilted wave fronts. Self-consistent
evolution of the optical and terahertz pulses is investigated. The red shift of the pumping pulse spectrum and the formation
of short-long-wave quasi-solitons are examined. 相似文献
6.
A. V. Ovchinnikov O. V. Chefonov M. B. Agranat K. A. Grishunin N. A. Il’in R. V. Pisarev A. V. Kimel A. M. Kalashnikova 《JETP Letters》2016,104(7):441-448
Optical second harmonic generation at the photon energy of 2?ω = 2eV in the model centrosymmetric antiferromagnet NiO irradiated with picosecond terahertz pulses (0.4–2.5 THz) at room temperature is detected. The analysis of experimental results shows that induced optical second harmonic generation at the moment of the impact of a terahertz pulse arises through the electric dipole mechanism of the interaction of the electric field of a pump pulse with the electron subsystem of NiO. Temporal changes in optical second harmonic generation during 7 ps after the action of the pulse are also of an electric dipole origin and are determined by the effects of propagation of the terahertz pulse in a NiO platelet. Coherent oscillations of spins at the antiferromagnetic resonance frequency induced by the magnetic component of the terahertz pulse induce a relatively weak modulation of magnetic dipole optical second harmonic generation. 相似文献
7.
Generation and characterization of terahertz pulse trains from biased, large-aperture photoconductors 总被引:2,自引:0,他引:2
The saturation properties of terahertz emission from biased, large-aperture photoconductors excited by trains of amplified femtosecond optical pulses are presented. A direct comparison is made of the multiple-pulse saturation properties of terahertz emission from semi-insulating GaAs and low-temperature-grown GaAs emitters with different carrier lifetimes. When the carrier lifetime is less than or comparable with the interpulse spacing, a significant enhancement of the narrow-band terahertz output is observed. The enhancement is not observed for emitters with long carrier lifetimes, consistent with the results of a previously derived saturation theory [Opt. Lett. 18, 1340 (1993)]. 相似文献
8.
9.
Intense radiation in the terahertz (THz) frequency range can be generated by focusing of an ultrashort laser pulse composed of both a fundamental wave and its second-harmonic field into air, as reported previously by Cook et al. [Opt. Lett. 25, 1210 (2000)]. We identify a threshold for THz generation that proves that generation of a plasma is required and that the nonlinearity of air is insufficient to explain our measurements. An additional THz field component generated in the type I beta-barium borate crystal used for second-harmonic generation has to be considered if one is to avoid misinterpretation of this kind of experiment. We conclude with a comparison that shows that the plasma emitter is competitive with other state-of-the-art THz emitters. 相似文献
10.
The dependence on optical energy of terahertz emission from air plasma induced by two-color femtosecond laser-pulses 下载免费PDF全文
The generation of terahertz (THz) emission from air plasma induced by two-color femtosecond laser pulses is studied on the basis of a transient photocurrent model. While the gas is ionized by the two-color femtosecond laser-pulses com- posed of the fundamental and its second harmonic, a non-vanishing directional photoelectron current emerges, radiating a THz electromagnetic pulse. The gas ionization processes at three different laser-pulse energies are simulated, and the corresponding THz waveforms and spectra are plotted. The results demonstrate that, by keeping the laser-pulse width and the relative phase between two pulses invariant when the laser energy is at a moderate value, the emitted THz fields are significantly enhanced with a near-linear dependence on the optical energy. 相似文献
11.
G. K. Abgaryan Yu. H. Avetisyan A. H. Makaryan V. R. Tadevosyan 《Journal of Contemporary Physics (Armenian Academy of Sciences)》2016,51(1):35-40
A new scheme for the efficient generation of broadband terahertz radiation via optical rectification of femtosecond laser pulses in the single-domain lithium niobate crystal equipped with the step-wise phase mask (SPM) is investigated. It is shown that using the SPM one can provide the phase matching for all the spectral components of a terahertz pulse by providing the effective conversion of laser radiation in the terahertz region. The angular distribution of spectral components, as well as the temporal shape of terahertz pulses in the wave zone is studied. These results can be applied in the time-domain spectroscopy, the imaging of hidden objects, and etc. 相似文献
12.
13.
The possibility of efficient terahertz generation via optical rectification in electro-optic crystal doped with the two-level resonant impurities is demonstrated. Under conditions of the self-induced transparency regime the laser pulses slows down to achieve the phase matching condition. The terahertz generation is accompanied by periodic modulation and spectral deformation of the laser pulse. The most efficient generation occurs under condition of small negative detuning from the resonant frequency of the two-level system. 相似文献
14.
A. A. Frolov A. V. Borodin M. N. Esaulkov I. I. Kuritsyn A. P. Shkurinov 《Journal of Experimental and Theoretical Physics》2012,114(6):893-905
A theory is developed for calculating the spectrum and the shape of a terahertz wave packet from the temporal profile of the energy of the second harmonic of the laser field generated during nonlinear interaction of laser and terahertz pulses in an optical-breakdown plasma. The spectral and temporal characteristics of the second-harmonic envelope and a terahertz pulse are shown to coincide only for short laser pulses. For long laser pulses, the second-harmonic spectral line shifts to the red and its temporal profile is determined by the time integral of the electric field of terahertz radiation. 相似文献
15.
R. A. Akhmedzhanov A. I. Korytin A. G. Litvak A. M. Sergeev E. V. Suvorov 《Radiophysics and Quantum Electronics》2005,48(10-11):837-843
We present experimental results on generation of pulsed terahertz radiation in a ZnTe crystal using nonlinear optical rectification of high-power femtosecond laser pulses. The use of terahertz pulses for spectroscopy is tested in the rotational lines of absorption of water vapors in the atmosphere. Panoramic spectra of absorption of a number of solvents and protein solutions are measured in the range from 0.2 to 2 THz. 相似文献
16.
We report on efficient THz pulse generation via optical rectification with femtosecond laser pulses focused to a line by a cylindrical lens. This configuration provides phase-matched conditions in the superluminal regime. 35 pJ THz pulses have been generated with this technique in a stoichiometric LiNbO3 crystal pumped by 2 μJ femtosecond laser pulses at room temperature. An unusual superquadratic rise of the THz pulse energy with the laser pulse energy has been observed at high laser energies. This extraordinary energy dependence of the THz generation efficiency is explained by self-focusing of the laser beam in the crystal. Z-scan measurements and comparison of the THz pulse spectra created with laser pulses having different energies confirm this interpretation. 相似文献
17.
A new nonlinear optical phenomenon—generation of surface waves by a drag current appearing at an inclined incidence of a focused femtosecond laser pulse—has been theoretically described. The generated waves have terahertz frequencies and their total energy increases with an increase in the effective frequency of electron–electron collisions and with a decrease in their density. 相似文献
18.
Percolation-enhanced generation of terahertz pulses by optical rectification on ultrathin gold films
Emission of pulses of electromagnetic radiation in the terahertz range is observed when ultrathin gold films on glass are illuminated with femtosecond near-IR laser pulses. A distinct maximum is observed in the emitted terahertz amplitude from films of average thickness just above the percolation threshold. Our measurements suggest that the emission is through a second-order nonlinear optical rectification process, enhanced by the excitation of localized surface plasmon hot spots on the percolated metal film. 相似文献
19.
D. L. Hovhannisyan V. O. Chaltykyan A. S. Martirosyan 《Journal of Contemporary Physics (Armenian Academy of Sciences)》2009,44(2):63-69
We present the results of theoretical studies of the process of generation of terahertz radiation arising via interaction of few-cycle laser pulses propagating in an isotropic nonlinear medium. Numerical time-integration, by the finite-difference method, of the system of nonlinear Maxwell equations has been performed. We consider the interaction of mutually-orthogonal linearly polarized pulses, both having the central wavelength of 1.98 μm, durations of 30 fs, and the energies of 30 nJ, propagating along the normal to the 〈110〉 plane in a 1 mm-thickness GaAs crystal. In the nonlinear part of the medium polarization the without-inertia nonlinear second-order susceptibility is taken into account. The process of formation of a terahertz pulse arising via spectral filtration of supercontinuum formed in the spectra of pump pulses at the output of nonlinear crystal is studied. The dependences of both the current frequency of the pump pulses on time for different lengths of nonlinear crystal and of pump pulse durations on the crystal length are obtained. Also the dependences of the current frequency of the terahertz pulse on time at different crystal lengths, as well as of the efficiency of generation of terahertz radiation on the length of nonlinear crystal and on the energy of pump pulses are obtained. 相似文献
20.
Supercontinuous high harmonic generation from asymmetric molecules in the presence of a terahertz field 下载免费PDF全文
We have investigated high-order harmonic generation from asymmetric molecules. It is found that supercontinuous high harmonics,which are produced from asymmetric molecules by significantly steering the ionization,are broken down when the electric field of the 5-fs driving laser pulse is increased to 0.16 a.u. The high harmonic generation from asymmetric molecules with the presence of a terahertz field is also investigated. This reveals that the terahertz controlled laser pulse significantly increases the energy difference between photons,emitted from the ejected electrons,in the first and second halves of the optical cycle at the centre of the driving laser pulse. In this way,a 200-eV broadband supercontinuum can be produced in the plateau,from which a 60-as pulse with a bandwidth of 60 eV can be directly obtained with a minor post-pulse. 相似文献