Intensity,correlations, and linewidths of two mode lasers with intensity coupling near threshold

Two mode lasers with intensity coupling are treated by simple fluctuation theory. The intensities of the two modes as functions of pump power are calculated together with the correlation matrix. Equations of motion for the intensities are derived from which the decay times of correlations are found by a method of quasilinearization as well as by decoupling the hierarchy of correlation functions. Details of photon fluctuation linewidths are reported together with the time dependent correlations between different modes.     

Measurements of someK-internal conversion coefficients near threshold

TheK-internal conversion coefficients have been measured by the XPG technique for a number of low energyγ-ray transitions whose energies do not exceed theK-binding energies by more than 4 keV. Using Si(Li) detectors in singles and coincidence arrangements, the following results were obtained: 63.1 keV El in¹⁶⁹Tm(α_K=1.02±0.15), 72.0 keV E1 in¹⁸⁷Re (0.75±0.05), 57.8 keV M1 in¹⁶²Ho (11.42±0.67), 56.6 keV M1 in¹⁶⁴Ho (12.04±0.70), and 67.1 keV M1 in¹⁷⁴Lu(10.25±0.58). The experimental results are compared with the theoretical calculations which include transition energies down to 1 keV above threshold.     

Correlation function of the amplitude and of the intensity fluctuation for a laser model near threshold

In extension of a preceding paper the correlation function of the amplitude and of the intensity fluctuation are calculated in the threshold region. The laser amplitude is treated as a classical random variable obeying a van der Pol equation with a noise term. In order to get correlation functions, the method of distribution functions is employed. The distribution functions are evaluated by the Fokker-Planck equation. The lowest eigensolutions of the Fokker-Planck equation are obtained approximately by a variational method.     

Intensities and correlations in two-mode lasers near threshold

Static photon intensities and correlations, intensity linewidths, and transient behaviour of a two-mode laser near and between the modes' thresholds have been calculated as functions of external pumping, of the coupling strength between the modes, and of detuning. Several curves, summarizing our results, are reported and discussed.     

Photon statistics of a bad-cavity laser near threshold

A simple model of a bad-cavity laser is presented based on Haken's master equation for N pumped two-level atoms in a cavity. Via adiabatic elimination of fast variables the whole photon statistics is solved analytically near threshold. It is shown that the second order coherence function g ⁽²⁾ (0) has a very different behavior near threshold for a bad-cavity laser compared to a good-cavity laser. The power spectrum illustrates nicely the different time scales involved in the dynamics. Received: 13 November 1998 / Revised: 19 May 1998 / Accepted: 6 July 1998     

自由运转半导体激光器边模间的强度关联

半导体激光器的强度和相位起伏一直是影响其应用的关键所在.在实验上研究了自由运转模式下半导体激光器的强度噪声.采用自制的分辨率为0.01 nm的光谱仪成功地分辨出数十个边模，并利用射频低噪声光电探测器系统，分析了激光器的主模与边模之间以及各边模之间的强度噪声关联特性.从实验上证实了主模与边模之间的负关联效应，同时观察到边模之间存在的周期性负关联.该结果对进一步认识半导体激光器噪声的产生机制及强度压缩光的产生机制具有重要意义. 关键词： 半导体激光器 强度噪声 负关联     

Level structure of20Na near the proton threshold

The excitation energies of states in²⁰Na near the proton threshold have been measured with the²⁰Ne(³He, t)²⁰Na charge exchange reaction. The possible implications of these states for the stellar reaction rate of¹⁹Ne(p,γ)²⁰ Na are discussed.     

Quantum communication exploiting above threshold OPO intensity correlations and polarization encoding

We present a continuous variable quantum communication protocol based on bright continuous-wave twin-beams generated by a type-II OPO. Intensity correlation between the beams is used in conjunction with a binary randomization of polarization to guarantee security and reveal eavesdropping actions. The scheme presented is asymmetric. Bob (the receiver) retains one of the beams and sends the other one to Alice after a random rotation of its polarization. The cryptographic key elements are encoded through amplitude modulation by Alice, who sends back her beam to Bob after a second rotation of the polarization. Eventually, the beams are detected by Bob after a further random polarization rotation. The security of the system and the possibility of revealing the eavesdropping action in the case of an individual attack are demonstrated by evaluating the bit error rates.     

Linewidth of a detuned single mode laser near threshold

The linewidth of a detuned single mode laser is calculated. Using the Fokker-Planck equation method, the problem is reduced to a nonhermitian eigenvalue problem. Numerical results near threshold and an approximate linewidth formula are given.     

The fine structure of the recovering auditory detection threshold.

Detection thresholds were gathered for a 2 kHz Gaussian-shaped probe (standard deviation = 0.5 ms), centered at intervals of as little as half a millisecond over 0-30 ms following a 200 ms, 97 dB SPL, 2 kHz tone. Surprisingly, there were small, sudden rises and falls superimposed on each subject's generally smooth recovery. Even more obvious were nonmonotonicities in the standard deviation of the cumulative normal fitted to each threshold's psychometric function.     

On the theory of a detuned single mode laser near threshold

A theory of a detuned single mode laser near threshold is given using the Fokker-Planck equation technique. The Fokker-Planck equation is solved by an eigenfunction expansion. The eigenfunctions and the corresponding eigenvalues are determined by a nonhermitian operator and are calculated numerically in the threshold region. The dependence of the linewidth from the detuning is shown. In the intensity distribution the detuning enters only via a change of the scaling parameter. For the linewidth, however, an additional broadening is found. Finally it is shown that in certain cases the correlation function must not be approximated by a single exponential term.     

准分子宽带泵浦碱金属激光器泵浦特性分析

建立了以Rb-Ar混合气体为增益介质的四能级准分子宽带泵浦碱金属激光器(XPAL)含时速率方程模型,计算得到了运转过程各能级粒子数和腔内激光强度随时间的变化曲线。结果表明:XPAL的阈值泵浦强度很高,泵浦源谱宽与吸收线宽匹配不能达到提高吸收效率、降低阈值的目的; 在泵浦功率一定的条件下, 增加介质长度和温度可以提高吸收效率,但将降低单位体积泵浦速率; XPAL成功的关键在于实现有效的泵浦吸收。     

Correlation functions for a laser with saturable absorber near threshold

We study in the threshold region the relaxation times and the correlation functions of the field amplitude and of the intensity fluctuations for a solid-state laser containing a saturable absorber in the domain of the parameter space where bistability can occur. We show that the relaxation times display in a small domain above threshold a net-like structure which disappears in the polynomial approximation. The noise spectrum is nearly lorentzian only in a very small domain around the transition point and well above threshold. The line-width displays the well-known sharpening at and above threshold.Supported in part by the Polish Ministry of Science, Technology and Higher Education, Project M.R.I.7Chercheur qualifié F.N.R.S.     

The fine structure of the spectrum of the electronic NO laser

The spectrum of the electronic NO laser has been photographed with high resolution in the region 10 100–10 500 Å. It shows the band system F²Δ-C²Π whose upper and lower states are both Rydberg states configurationally mixed with valence states. Only predissociated rotational levels of the lower state appear in the spectrum. For v = 0 of C²Π a single mixed level $\text{T}{}_{\mathrm{y}}\text{(J = 5}\text{1}\text{2}\text{) = 52431}\text{cm}{}^{\mathrm{?1}}$, very close to the dissociation limit, gives rise to laser lines.     

Extended x-ray absorption fine structure study of local structure and atomic correlations of tellurium nanoparticles

Extended x-ray absorption fine structure measurements were performed on trigonal tellurium (t-Te) and tellurium nanoparticles in very thin films. Twofold coordinated chains, much like those in t-Te, exist even in the nanoparticles, but covalent bonds or intrachain interactions are stronger than those of t-Te as shown by a shorter bond length and higher Einstein temperature. The interchain coordination number of the nanoparticles is about half that of t-Te, suggesting reduction of interchain interactions.     

Theoretical investigation on the threshold value of stimulated Brillouin scattering in terms of laser intensity

The threshold value of stimulated Brillouin scattering (SBS) was investigated theoretically basing on a new concept of real gain length (RGL). It shows that for ideal steady-state SBS or ideal transient SBS, the threshold values are both constants and the later is five orders of magnitude larger than the former. Under general conditions, whether steady-state SBS or transient SBS will occur is determined by RGL. The SBS occurred in a long material may not be steady-state SBS.     

Disordered magnet near the percolation threshold

A disordered Potts magnet containing a random mixture of ferromagnetic exchange constants J_a and J_b (J_a?J_b) near the percolation threshold is considered. The scaling form for the free energy contains two crossover exponents. Duality arguments in two dimensions show that these exponents are equal. They are also shown to be equal to unity in d = 6 ? ? dimensions to order ?.     

Gamow-Teller strength near the pion threshold

The Gamow-Teller strength at high energy, in the vicinity of the pion mass, is linked to the absorption of p wave pions. It is not subject to Pauli blocking and increases linearly with the nucleon number.