Amplification of fluorescence using collinear picosecond optical parametric amplification at degeneracy

We demonstrate the output characteristic of broadband parametric amplification of incoherent light pulses in a 355-nm pumped degenerate picosecond optical parametric amplification with either saturated or unsaturated amplification.The optical parametric amplifier is seeded by the fluorescence generated in a solution of pyridine-1 dye in ethanol.With the saturated amplification,we can obtain high energy incoherent light pulses,whose full width at half maximum bandwidth varies from 16 nm to 53 nm for the different phase matching angles near degeneracy.Moreover,the unsaturated bandwidth of the amplified pulses fits well to the calculated result at degeneracy.Selecting s-polarized fluorescence with a Glan-Taylor prism,the maximum bandwidth of the amplified fluorescence is found to be 59 nm for a purely s-polarized seed.The maximum output energy is 0.67 mJ for the optical parametric amplifier.By using an optical filter and compressor,the generated high energy incoherent light has great potential as the incoherent pump,signal or idler wave of a parametric down-conversion process,so that a wave with a high degree of coherence can be generated from an incoherent pump light.     

Microlaser-pumped periodically poled lithium niobate optical parametric generator-optical parametric amplifier

For what is believed to be the first time, a single-longitudinal-mode passively Q-switched Nd:YAG microlaser is used to pump a narrow-bandwidth periodically poled lithium niobate (PPLN) optical parametric generator-optical parametric amplifier (OPG-OPA). Before amplification in the OPA, the output of the OPG stage was spectrally filtered with an air-spaced etalon, resulting in spectroscopically useful radiation (bandwidth, ~0.05 cm(-1) FWHM) that was tunable in 15-cm(-1) segments anywhere in the signal range 6820-6220 cm(-1) and the idler range 2580-3180 cm(-1). The ability to pump an OPG-OPA with compact, high-repetition-rate, intrinsically narrow-bandwidth microlasers is made possible by the high gain of PPLN. The result is a tunable light source that is well suited for use in portable spectroscopic gas sensors.     

Pump-enhanced optical parametric oscillator generating continuous wave tunable terahertz radiation

We demonstrate a tunable cw terahertz (THz) parametric oscillator based on periodically poled MgO-doped lithium niobate, directly converting the 1030 nm pump wave into the THz regime. The tunability ranges from 1.2 to 2.9 THz at output power levels between 0.3 and 3.9 μW. To overcome the high pump threshold caused by THz absorption in the nonlinear crystal, we employ an enhancement cavity with a finesse of 500 at the pump wavelength. The intracavity pump threshold at 1.4 THz is measured to be 350 W for a crystal length of 2.5 cm.     

Electromagnetically induced transparency in quantum dot biexciton–exciton cascaded scheme

We numerically investigated the electromagnetically induced transparency in the quantum dot biexciton–exciton scheme. Through calculating the density matrix equation in the steady state, we obtain the electromagnetically induced transparency absorption dip with different pump intensity and biexciton decay rate. The refractive index is also calculated. We analyze the biexciton energy renormalization and pump pulse intensity influencing on the EIT dip and the slow factor. The slow factor decreases from about 3000 to 2000 due to the renormalization. It shows better temperature stability for stronger confinement energy and smaller decay rate compared with quantum well.     

Adjusting the properties of the photon generated via an optical parametric oscillator by using a pulse pumped laser

The cavity-enhanced spontaneous parametric down-conversion far below threshold can be used to generate a narrow-band photon pair efficiently. Previous experiments on the cavity-enhanced spontaneous parametric down-conversion almost always utilize continuous wave pump light, but the pulse pumped case is rarely reported. One disadvantage of the continuous wave case is that the photon pair is produced randomly within the coherence time of the pump, which limits its application in the quantum information realm. However, a pulse pump can help to solve this problem. In this paper, we theoretically analyze pulse pumped cavity-enhanced spontaneous parametric down-conversion in detail and show how the pump pulse affects the multi-photon interference visibility, two-photon waveform, joint spectrum and spectral brightness.     

Quantum-Statistics Behavior of the Exciton-Biexciton System In GaAs/AlAs Type-II Superlattices

We have investigated the quantum-statistics behavior of the exciton-biexciton system from the photoluminescence properties in (GaAs) m /(AlAs) m type-II superlattices with m = 12 and 13 monolayers, where the lowest-energy type-II exciton consists of the n = 1 X electron of AlAs and n = 1 o heavy hole of GaAs. The long exciton lifetime of the order of w s due to the indirect transition nature enables us to obtain precisely the density relation between the exciton and biexciton from the line-shape analysis of time-resolved photoluminescence spectra. In a relatively low exciton-density region, the biexciton density obeys a well-known square law. At an exciton density around 1 2 10 10 cm m 2 , the biexciton density suddenly increases with a threshold-like nature. This behavior, which is realized at a bath temperature up to 8 K under an excitation power of the order of 100 mW/cm 2 , results from the characteristics of Bose-Einstein statistics of the exciton-biexciton system.     

Pressure-induced threshold optical pump intensity in a CdTe/ZnTe quantum dot

Pressure-induced binding energies of an exciton and a biexciton are studied taking into account the geometrical confinement effect in a CdTe/ZnTe quantum dot. Coulomb interaction energy is obtained using Hartree potential. The energy eigenvalue and wave functions of exciton and the biexciton are obtained using the self-consistent technique. The effective mass approximation and BenDaniel-Duke boundary conditions are used in the self-consistent calculations. The pressure-induced nonlinear optical absorption coefficients for the heavy hole exciton and the biexciton as a function of incident photon energy for CdTe/ZnTe quantum dot are investigated. The optical gain coefficient with the injection current density, in the presence of various hydrostatic pressure values, is studied in a CdTe/ZnTe spherical quantum dot. The pressure-induced threshold optical pump intensity with the dot radius is investigated. The results show that the pressure-induced electronic and optical properties strongly depend on the spatial confinement effect.     

Difference frequency generation combined with intracavity absorption

A previous study in which the optical parametric oscillator (OPO) has been shown to provide a light source suitable for intracavity absorption spectroscopy, is extended to difference frequency generation. The following experimental situation is discussed: in a nonlinear material an incident monochromatic pump wave, together with an incident many-mode idler wave, creates a many-mode wave at the difference frequency (signal wave) which is made to resonate in a cavity. The latter contains an absorbing medium whose absorption line is smaller than the signal bandwidth. For this device, the enhancement factor ξ is calculated. Large values of ξ can be expected only for pump powers which exceed the threshold value for optical parametric oscillation. Otherwise, the enhancement will be due only to the resonator effect.     

Noncascading THz-wave parametric oscillator synchronously pumped by mode-locked picosecond Ti:sapphire laser in doubly-resonant external cavity

A noncascading terahertz (THz) wave parametric oscillator synchronously pumped by a mode-locked picosecond Ti:sapphire laser whose average power was less than 1 W was demonstrated with a noncollinear phase-matching MgO:LiNbO₃ crystal in an external enhancement cavity doubly resonant for both pump (780 nm) and signal (781-784 nm) waves. In the external cavity, in which the pump wave enhanced so as to reduce the pumping threshold of parametric processes, the signal wave could also resonate and thus be enhanced simultaneously, resulting in a THz wave output at approximately 0.9 THz as the idler wave. The novel dual enhancement of pump and signal waves reduced the threshold pumping intensity to approximately 50 MW/cm², which was much lower than that of a conventional externally pumped THz wave parametric oscillator with a crystal.     

Phase Effects of the Parametric Interaction in Metamaterials

We study the phase effects of the three-wave parametric interaction in metamaterials considering the negative refraction at the frequency of a signal wave. We analyze the efficiency of energy conversions between two direct waves with respect to the energy of the backward signal wave along with the dynamics of the signal-wave amplification in metamaterials. We show that there exist optimum values of the fundamental-wave intensity and the phase mismatch at which the efficiency of conversion is maximum. We obtain an analytic expression for the optimum value of the relative length of the metamaterial and present a numerical evaluation of the expected value for efficiency of the frequency parametric conversion in dielectric waveguides. A sufficient enhancement in the signal-wave amplification, which is possible at optimum values of the pump intensity and the metamaterial total length, leads to the parametric generation of the signal wave. Changing the frequency and power of the pump wave, one can realize a regular tuning of the frequencies of parametric converters.     

Threshold Analysis of a THz-Wave Parametric Oscillator

The parametric gain of a terahertz wave parametric oscillator （TPO） is analyzed. Meanwhile the expression of TPO threshold pump intensity is derived and theoretically analyzed with different factors. The effective interaction length between the pump wave and Stokes wave is calculated, and particular attention is paid to the coupling efficiency of the pump wave and Stokes wave. Such an analysis is useful for the experiments of TPO.     

Biexciton in II–VI quantum dots with different localization potentials

We present a comparative study of the influence of the form of a localization potential on the binding energy of the biexciton in spherically symmetric quantum dots based on II–VI compounds. The proposed criterion for the comparison of potentials of different forms—the box potential, the harmonic oscillator, and the Gaussian potential—is based on the identical localization of charge carriers of the same sign in these potentials. Calculations of the biexciton binding energy have been performed using the variational method within the framework of the kp-perturbation theory taking into account additional polarization terms in the wave functions of the electron and hole subsystems, as well as the complex structure of the valence band. The obtained results have demonstrated that the presence of a smoothly varying finite-height potential in Cd(Zn)Se/ZnSe quantum dots can lead to a more efficient localization in the case of the biexciton in comparison with the exciton, which is of interest for the implementation of fast-acting quantum light emitters.     

Theorie der parametrischen Vier-Photonen-Wechselwirkung. II., Verstärkung und Oszillation in der Näherung des vorgegebenen Pumpfeldes)

The processes of parametric amplification and oscillation in a medium with cubic polarization is investigated in parametric approximation. For the case of amplification the threshold power of the pump wave is calculated. The influence of a finite phase mismatching and of the initial phases on the amplification process is discussed. For larger values of mismatching a periodical change between amplification and depletion may appear. For the cases of a single resonant oscillator (for the signal wave only), a double resonant oscillator (for both signal and idler wave) and a double resonant oscillator with the pump wave reflected at the second mirror the threshold power of the pump wave and the rise time are calculated. Characteristic differences between four-photon and three-photon parametric oscillators are discussed. A numerical estimation of the threshold power for some media with nonlinear susceptibilities known from literature leads to the conclusion that the realization of a four-photon parametric oscillator should be possible. In the appendix we discuss the influence of diffraction, focussing, birefrigence, nonstationarity and depletion of the pump wave on the studied process as well as the conditions under which these effects can be neglected.     

对应于铯原子D1线连续可调谐正交压缩态光场的制备

铯原子D₁线的非经典光由于其波长接近于量子点的独特优势,在固态量子信息网络的发展中有着重要的应用前景.在之前的工作中,利用两镜连续简并光学参量振荡器中的参量下转换过程,制备出2.8 d B正交压缩真空态光场.然而,所产生光场的压缩度较低,对于对压缩光具有实用意义的可调谐性能也未做进一步探究.理论分析表明,光学参量振荡器后腔镜对信号光透射率的增加及内腔损耗的减小可以提高压缩度.因此,本文在该研究基础上,通过使用高光洁度腔镜及优化腔镜镀膜参数等方式对光学参量振荡器进行改良,降低了光学参量腔阈值,获得压缩度为3.3 d B的单模正交压缩真空光.当光学参量腔运转为参量反放大状态时,在系统稳定运行的情况下,制备的明亮压缩态光场能够连续调谐80 MHz,为其在量子信息网络中的应用奠定了良好的基础.     

Enhanced terahertz-wave parametric generation and oscillation in lithium niobate waveguides at terahertz frequencies

We observed parametric-generation efficiency of 1.61% from 1064 to 1071 nm and at 162 microm in a 0.5 mm thick, 45 mm long z-cut congruent lithium niobate waveguide with a pump energy of 2.2 mJ and a pump pulse width of 5.8 ns. We also measured an ultralow-threshold intensity of 70 MW/cm2 for a 1064 nm pumped parametric oscillator resonating at 1071 nm and emitting at 162 microm with a 1 mm thick, 45 mm long lithium niobate waveguide.     

Four-magnon decay of magnetostatic surface waves in yttrium iron garnet films

The four-magnon instability of magnetostatic surface waves (MSSWs) in yttrium iron garnet epitaxial films is investigated experimentally. It is shown that four-magnon instability for MSSWs with wave numbers 30–600 cm⁻¹ is a decay instability and develops for values of the wave magnetization close to the threshold level for second-order parametric instability of a homogeneous transverse pump wave. When the supercriticality of the MSSW power is 15–20 dB, the generated parametric spin waves themselves become unstable with respect to the four-magnon interaction, so that kinetic instability develops in the film. It is shown that the pump signal transmitted through the signal and the length of the “nonlinear” part of the film, where a MSSW is capable of exciting parametric spin waves, increase as the pump power is increased. Fiz. Tverd. Tela (St. Petersburg) 38, 330–338 (February 1997)     

周期极化掺镁铌酸锂光学参量振荡器时域特性的实验研究

分别采用MOTORULA公司的硅基光电二极管探测器和JUDSON公司的InGaAs光电二极管探测器对泵浦光和信号光的脉宽进行了测量.研究了极化周期、工作温度以及抽运功率与周期极化掺镁铌酸锂光学参量振荡器输出的信号光脉冲宽度的作用关系.实验采用LD端面抽运的声光调Q Nd∶YVO4激光器作为抽运源,在晶体温度为30 ℃、极化周期为29.5 μm条件下,当抽运功率为1 008 mW时,获得了平均功率为238 mW的信号光输出,其光-光转换效率为23.6%,最窄脉冲宽度约为9.3 ns,相对抽运光脉宽被明显压窄.     

Tunable fiber-optic parametric oscillator

We report operation of a tunable optical parametric oscillator that employs a nonlinear-fiber Sagnac interferometer as a parametric amplifier. The amplifier, which consists primarily of dispersion-shifted fiber that has zero dispersion at 1538 nm, is synchronously pumped with 7.7-ps pulses at 1539 nm. The wide bandwidth of the parametric gain permits tuning of the output signal pulses over a 40-nm range centered on the pump wavelength. The Sagnac interferometer decouples the pump wave from the oscillator cavity while a bandpass filter in the cavity transmits only the signal wave, thereby creating a singly resonant parametric oscillator that is phase insensitive. Whereas we demonstrate tuning over almost the entire bandwidth of Er-doped-fiber amplifiers, one could construct a similar device that operates near the 1310-nm zero-dispersion wavelength of standard telecommunication fiber.     

Electromagnetically induced transparency-like effect in the degenerate triple-resonant optical parametric amplifier

We investigate experimentally the absorptive and dispersive properties of the triple-resonant optical parametric amplifier (OPA) for the degenerate subharmonic field. In the experiment the subharmonic field is utilized as the probe field and the harmonic wave as the pump field. We demonstrate that the electromagnetically induced transparency (EIT)-like effect can be simulated in the triple-resonant OPA when the cavity linewidth for the harmonic wave is narrower than that for the subharmonic field. However, this phenomenon cannot be observed in a double-resonant OPA. The narrow transparency window appears in the reflected field. Especially in the measured dispersive spectra of the triple-resonant OPA, a very steep variation of the dispersive profile of the subharmonic field is observed, which can result in a slow light as that observed in an atomic EIT medium.     

Effect of idler absorption on efficiency of optical parametric oscillators

Idler wave absorption is important in optical parametric oscillators (OPOs). We show through both numerical simulation and experiment that proper idler wave absorption coefficient could make OPOs perform better in conversion efficiency. If the coefficient becomes larger or smaller than the proper value, the conversion efficiency would be lower. A periodically poled lithium niobate (PPLN) OPO is set to verify the numerical results. Moreover, different pump power is used in the experiment research. It shows that the proper value is changing with the pump power. It shows that idler wave absorption should be considered comprehensively with pump wave power in efficiency OPO designing.