Emission Spectra of a Two-level Atom Under the Presence of Another Two-level Atom

Abstract

We investigate the spectrum of light emitted by a two-level atom interacting with another two-level atom inside an ideal cavity within the frame of generalized Jaynes-Cummings model. The influence of various ratios of the coupling constants of the atoms to the field on the spectrum of the emitted light is studied in detail for the case when the atoms are supposed to be initially in the excited state and the field in a Fock state as well as their superposition.     

Second Harmonic Generation in a Free Electron Laser

It is pointed out that in a free electron laser higher frequencies, which are very nearly equal to the harmonics, are generated. Second harmonic generation, in stimulated emission in a spatially periodic static magnetic field, is studied using the Feynman diagram technique. The ratio of gain for the second harmonic compared to that of the fundamental harmonic is of the order of 10 ^?9 for the conditions present in the free electron laser of Deacon et al. [1].     

Emission Spectra of a Two-level Atom in a Kerr-like Medium

Abstract

We have investigated the spectrum of light emitted by a single atom interacting with a single mode of the radiation field in an ideal cavity filled with a Kerr-like medium. It is shown that owing to the Kerr-like nonlinearity in the system the spectrum of the emitted light exhibits a single-peaked structure for sufficiently high intensities of the initial coherent field instead of the triplet structure in the case of the standard Jaynes-Cummings model.     

Interaction of a Two-level Atom with Squeezed Light

The dynamic response of the inversion in a two-level atom to single-mode squeezed states of the radiation field is examined. Depending on the direction of squeezing, an increase or decrease in the collapse time is demonstrated. A number of additional departures from the response of the atom to a coherent field are noted. In particular, for certain squeezed states the response of the atom is similar to that expected for chaotic radiation.     

Second Harmonic Generation as a Tool for Measuring Mode Coupling,Pulse Length and Mode Size in Short Laser Pulses

Abstract

We report on a detailed analysis of second harmonic generation with a multi-modal beam for a non-collinear geometry. As a result some improvements for a picosecond pulse width analyser are suggested. Experimental results relative to both a free electron laser and to a mode locked Nd: YAG laser are discussed. This modified version of the pulse analyser is able to monitor, in real time, the relative pulse-to-pulse change of mode size, pulse length and mode mixing effect independently of the pulse length from femtoseconds to milliseconds.     

高强度超短脉冲单块BBO晶体的三倍频研究

对高强度超短脉冲单块BBO晶体产生三倍频的过程进行了理论及实验研究.定量分析入射基频光强度、晶体厚度、晶体失谐角和方位角等因素对三倍频光转换效率和时间波形的影响,并对实验参数进行了优化.针对脉冲宽度100 fs、带宽25nm、中心波长810 nm、能量为6 mJ左右的超短脉冲基频光,采用单块BBO晶体开展了三倍频实验研究,获得了0.8%的三倍频转换效率,并对实验结果进行了分析.在此基础上,进一步提出了提高单块BBO晶体超短脉冲三倍频转换效率的改进措施.     

Photon Conversion among Multichromatic Waves in Two-level Atom Systems

Abstract

In this paper, we shall discuss a generalized version of the Jaynes-Cummings model in which a two-level atom is coupled to multichromatic waves with general frequencies and coupling constants. We shall show that this two-level atom system can be mapped into an effective model in which a quantum particle moves in a lattice whose sites specify the number of photons in the multichromatic waves. In general, when the number L of modes is greater than two, large energy exchanges among different monochromatic waves are possible (L = 2 is a special case; exchanges of a large number of photons are possible only for degenerate modes). Depending on the frequencies of the elecromagnetic modes, we can classify the two-level systems in two categories. In one case, the eigenfunctions of the quantum particle are extended and thus exchange of a large number of photons is possible. In the other case, the eigenfunctions of the quantum particle are localized and exchange of a large number of photons is greatly suppressed.     

SnSe2 Nanosheets for Subpicosecond Harmonic Mode‐Locked Pulse Generation

Tin diselenide (SnSe₂) nanosheets as novel 2D layered materials have excellent optical properties with many promising application prospects, such as photoelectric detectors, nonlinear optics, infrared photoelectric devices, and ultrafast photonics. Among them, ultrafast photonics has attracted much attention due to its enormous advantages; for instance, extremely fast pulse, strong peak power, and narrow bandwidth. In this work, SnSe₂ nanosheets are fabricated by using solvothermal treatment, and the characteristics of SnSe₂ are systemically investigated. In addition, the solution of SnSe₂ nanosheets is successfully prepared as a fiber‐based saturable absorber by utilizing the evanescent field effect, which can bear a high pump power. 31st‐order subpicosecond harmonic mode locking is generated in an Er‐doped fiber laser, corresponding to the maximum repetition rate of 257.3 MHz and pulse duration of 887 fs. The results show that SnSe₂ can be used as an excellent nonlinear photonic device in many fields, such as frequency comb, lasers, photodetectors, etc.     

Pulse Propagation in a Gaseous Laser Amplifier

Abstract

It is shown that some transversal profile modifications, such as ‘overshoot’ at the edges of laser pulses propagating through gaseous laser amplifiers, can be qualitatively explained when diffusion of the active centres of the amplifier is taken into account. The necessary conditions for this situation to occur are also discussed and numerical results are presented which are in good agreement with previously obtained experimental results.     

Self-induced Temperature Profile and Inhomogeneity Effect on Second Harmonic Generation Using Focused Laser Beam

The behaviour of optical second harmonic due to crystal inhomogeneity and self-induced thermal effect has been considered for a focused laser beam. Temperature profile created due to a fundamental laser beam along the crystal length shows an increase in temperature band width for various values of focusing parameter. Normalized second harmonic power in inhomogeneous crystals increases up to an optimum value of focusing parameter. Utility of focusing is limited due to formation of filament in crystal for higher values of focusing parameter.     

Angularly-resolved High-order Harmonic Generation in Helium

Abstract

Harmonics up to 119th have been generated in helium using a 1·053 μm, 1 ps chirped pulse amplification laser at intensities up to 3 × 10¹⁴W cm^?2, and their far-field spatial distributions have been measured. In the presence of considerable ionization, complex angular distributions are found for harmonics in the plateau region, while near the cut-off, their distribution narrows to approximately that predicted by lowest-order perturbation theory. The experimental results are found to be in good agreement with the predictions of a numerical propagation model which incorporates photoelectron dispersion and strong-field atomic data for the ionization rates and dipole moments.     

Second‐Harmonic Generation from a Single Core/Shell Quantum Dot

Nanoparticles emitting two‐photon luminescence are broadly used as photostable emitters for nonlinear microscopy. Second‐harmonic generation (SHG) as another two‐photon mechanism offers complementary optical properties but the reported sizes of nanoparticles are still large, of a few tens of nanometers. Herein, coherent SHG from single core/shell CdTe/CdS nanocrystals with a diameter of 10 to 15 nm is reported. The nanocrystal excitation spectrum reveals resonances in the nonlinear efficiency with an overall maximum at about 970 nm. Polarization analysis of the second‐harmonic emission confirms the expected zinc blende symmetry, and allows extraction of the three‐dimensional nanocrystal orientation. The small size of these nonlinearly active quantum dots, together with the intrinsic coherence and orientation sensitivity of the SHG process, are well adapted for ultrafast probing of optical near‐fields with high resolution as well as for orientation tracking for bioimaging applications.     

Pulse Shape Improvement in Core-Type High-Voltage Pulse Transformers With Auxiliary Windings

High-voltage pulsed power technologies are rapidly emerging as a key to efficient and flexible use of electrical power for many industrial applications. One of the most important elements in high-voltage pulse-generating circuit technology is the transformer, generally used to further increase the pulse output voltage level. However, its nonideal behavior has significant influence on the output pulse shape. The most attractive winding configuration for high-voltage, the core-type transformer with primary and secondary on different core legs, is seldom used in pulsed applications, because of its weak magnetic coupling between windings, which would result in a slow-rising output voltage pulse. This paper shows that auxiliary windings, suitably positioned and connected, provide a dramatic improvement in the pulse rise time in core-type high-voltage pulse transformers. The paper derives a mathematical model and uses it to describe the observed behavior of the transformer with auxiliary windings. It discusses experimental results, obtained from a high-voltage test transformer associated with a high-voltage pulse generating circuit, and the simulation results obtained from the numerical evaluation of the developed differential equations implemented in Matlab and taking into account the measured transformer parameters.      

Phonon Pulse Shape Discrimination in SuperCDMS Soudan

SuperCDMS is the next phase of the Cryogenic Dark Matter Search experiment, which measures both phonon and charge signals generated by particle recoils within a germanium target mass. Charge signals are employed both in the definition of a fiducial volume and in the rejection of electron recoil background events. Alternatively, phonons generated by the charge carriers can also be used for the same two goals. This paper describes preliminary efforts to observe and quantify these contributions to the phonon signal and then use them to reject background events. A?simple analysis using only one pulse shape parameter shows bulk electron recoil vs. bulk nuclear recoil discrimination to the level of 1:10³ (limited by the statistics of the data), with little degradation in discrimination ability down to at least 7?keV recoil energy. Such phonon-only discrimination can provide a useful cross-check to the standard discrimination methods, and it also points towards the potential of a device optimized for a phonon-only measurement.     

Bunching and Antibunching Effects in a System of N Two-level Atoms

Abstract

The problem of exhibiting bunching and antibunching phenomena for a system of N two-level atoms in interaction with light is investigated. The conditions for the change from bunching to antibunching and vice versa are obtained for resonance, and for time-independent and time-dependent coupling constant. The conditions for the case of resonance and time-independent coupling constant are investigated for both generalized coherent states and squeezed coherent states.     

Pulse Shaping in a Laser with an Irradiance-dependent Cavity Mirror

Abstract

The effect of an irradiance-dependent cavity mirror on the shape of a laser pulse is considered in the context of the CO₂ laser, using an InSb etalon as the mirror, with special reference to the production of square pulses. A dynamical instability is found experimentally, in numerical solutions of a rate equation model, and in a simplified stability analysis. This instability leads to a transient ringing, or even a train of short pulses rather than the more desirable long square pulse, unless the response time of the nonlinear mirror is very short.     

两水平无重复析因设计的一个散度效应检验方法

针对无重复两水平分式析因试验的一个散度效应识别问题,本文基于Score检验方法建立了一个散度效应识别方法。该方法可以用于已知某些散度效应存在的场合下检验其余因子的散度效应。     

Generation of Electron Bunches by an Ultrarelativistic Laser Pulse Intersecting the Boundary of an Inhomogeneous Plasma

Technical Physics Letters - The mechanism of generation of electron bunches upon the interaction of a laser pulse with a semibounded plasma having a diffuse boundary with vacuum in the form of a...