Quantum noise in the mirror–field system: A field theoretic approach

We revisit the quantum noise problem in the mirror–field system by a field-theoretic approach. Here a perfectly reflecting mirror is illuminated by a single-mode coherent state of the massless scalar field. The associated radiation pressure is described by a surface integral of the stress-tensor of the field. The read-out field is measured by a monopole detector, from which the effective distance between the detector and mirror can be obtained. In the slow-motion limit of the mirror, this field-theoretic approach allows to identify various sources of quantum noise that all in all leads to uncertainty of the read-out measurement. In addition to well-known sources from shot noise and radiation pressure fluctuations, a new source of noise is found from field fluctuations modified by the mirror’s displacement. Correlation between different sources of noise can be established in the read-out measurement as the consequence of interference between the incident field and the field reflected off the mirror. In the case of negative correlation, we found that the uncertainty can be lowered than the value predicted by the standard quantum limit. Since the particle-number approach is often used in quantum optics, we compared results obtained by both approaches and examine its validity. We also derive a Langevin equation that describes the stochastic dynamics of the mirror. The underlying fluctuation–dissipation relation is briefly mentioned. Finally we discuss the backreaction induced by the radiation pressure. It will alter the mean displacement of the mirror, but we argue this backreaction can be ignored for a slowly moving mirror.     

Noise performance of a feed-forward scheme for carrier-envelope phase stabilization

The noise performance of a feed-forward scheme for carrier-envelope phase stabilization is discussed. This scheme uses an acousto-optic frequency shifter to directly correct for fluctuations of the carrier-envelope phase in a pulse train emitted by a mode-locked laser without manipulating the intracavity dispersion. Generation of zero-offset frequency combs is demonstrated. Furthermore, it is shown that pump laser noise has only a minor effect on the achievable performance. Limited only by the travel time of the acoustic wave in the shifter, pump laser noise can be corrected up to near-megahertz frequencies, which yields superior noise performance compared to traditional feedback operation. Residual phase jitters down to 45 mrad are experimentally verified.     

Suppression of the intensity noise of a laser-diode-pumped single-frequency ring Nd:YVO(4)-KTP green laser by optoelectronic feedback

We investigate the different characteristics of the intensity noise of a laser-diode-pumped single-frequency ring Nd:YVO (4) laser and a Nd:YVO (4)-KTP green laser. By use of an optoelectronic feedback circuit connected directly to the pump current of the laser diode, the low-frequency intensity noise of the intracavity frequency doubler was suppressed to some extent.     

Chaos in a multimode solid-state laser system

When a nonlinear crystal is placed within a multimode solid-state laser cavity, deterministic fluctuations are induced in the output intensity. In this paper, the results of our studies of the intensity noise in a diode pumped, intracavity frequency doubled Nd:YAG (neodymium doped yttrium aluminum garnet) laser will be presented. First, a novel technique to eliminate these fluctuations is described. Second, the observation of antiphase states in the laser output is discussed. These states are characterized by a cyclic periodic pulsing of the individual longitudinal mode intensities. Finally, the statistical properties of chaotic intensity fluctuations are characterized. It is be demonstrated that it is possible to accurately model the laser dynamics by a system of globally coupled, nonlinear oscillators.     

Chaos control using notch filter feedback

A method for stabilizing periodic orbits and steady states of chaotic systems is presented using specifically filtered feedback signals. The efficiency of this control technique is illustrated with simulations (R?ssler system, laser model) and a successful experimental application for stabilizing intensity fluctuations of an intracavity frequency-doubled Nd:YAG laser.     

Laser stabilization with multiple-delay feedback control

Stabilization of chaotic intensity fluctuations of intracavity frequency-doubled solid-state (Nd: YAG) lasers using multiple-delay feedback control (MDFC) is demonstrated by numerical simulations. It is shown that MDFC not only provides stable (cw) output for constant pump rates but also works with slowly varying pump currents, resulting in corresponding (nonchaotic) intensity modulations.     

Delay control of coherence resonance in type-I excitable dynamics

We consider a simple paradigmatic system of type-I excitability subject to noise and time-delayed feedback. This system is governed by a global bifurcation, namely a saddle-node bifurcation on a limit cycle. In the absence of noise, delay can induce complex dynamics including multiple stable and unstable periodic orbits. Random fluctuations result in coherence resonance in dependence on the noise strength. We show that this effect can be enhanced by delayed feedback control with suitably chosen feedback strength and time delay.     

Quantum limits of cold damping with optomechanical coupling

Thermal noise of a mirror can be reduced by cold damping. The displacement is measured with a high-finesse cavity and controlled with the radiation pressure of a modulated light beam. We establish the general quantum limits of noise in cold damping mechanisms and we show that the optomechanical system allows to reach these limits. Displacement noise can be arbitrarily reduced in a narrow frequency band. In a wide-band analysis we show that thermal fluctuations are reduced as with classical damping whereas quantum zero-point fluctuations are left unchanged. The only limit of cold damping is then due to zero-point energy of the mirror. Received 1st August 2001 and Received in final form 12 October 2001     

介质参数对KrF激光放大器的影响

本文对对KrF激光产生的动力学过程及发光机制进行了研究,利用激发态二能级稳定态理沦,得到了介质的增益、饱和光强以及腔内最佳光强随介质成分和压强的依赖关系,可以作为准分子激光器介质参数选择的依据.并介绍一种用Goblin装置放大短脉冲的方法.     

Qauntum theory of two-photon absorption in a driven F-P cavity with the feedback of photon flux

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Giant fluctuations in the radiation intensity of two-dimensional electrons under quantum hall effect conditions

Giant fluctuations in the 2D-electron recombination radiation were studied in structures with a single or double GaAs quantum well under quantum Hall effect conditions. It is established that, if these conditions are exactly satisfied, the amplitude of the 2D-electron photoluminescence (PL) intensity is several orders of magnitude higher than the noise level, with the noise having a normal (Poisson) distribution. The fluctuations in the PL line intensity are accompanied by a jumpwise change in the line positions. Analogous jumps were also observed in the spectra of inelastic light scattering by 2D electrons in structures with a single GaAs quantum well. The fluctuation processes are correlated over macroscopic distances. The characteristic correlation length is 1–2 mm. The spectral density of giant fluctuations was found to exhibit narrow peaks. The ratios of the frequencies of these peaks are equal to those of Fibonacci numbers. The appearance of such frequencies in the fluctuation spectrum indicates that the fluctuations studied bear a resemblance to processes occurring in open dissipative dynamic systems. The methods developed in the theory of these systems can, in principle, be used to study giant fluctuations.     

Theory and experiment of CW dye laser injection locking and its application to second harmonic generation

High-power single-mode operation of a cw ring dye laser has been obtained by injection of cw single-mode radiation. The intracavity power of this system was used to generate tunable single-mode uv radiation by frequency doubling in a temperature phase-matched ADA crystal: up to 45 W intracavity fundamental power and up to 70 mW extracted uv power have been observed. A theoretical treatment of the injection locked cw ring dye laser system is given for the stationary state. Expressions for the intracavity intensities as a function of the small-signal gain and the saturation intensity are derived.     

Statistical properties of Er/Yb co-doped random Rayleigh feedback fiber laser

In this Letter, we experimentally investigate fast temporal intensity dynamics and statistical properties of the claddingpumped Er/Yb co-doped random Rayleigh feedback fiber laser(EYRFL) for the first time, to the best of our knowledge. By using the optical spectral filtering method, strong and fast intensity fluctuations with the generation of extreme events are revealed at the output of EYRFL. The statistics of the intensity fluctuations strongly depends on the wavelength of the filtered radiation, and the intensity probability density function(PDF) with a heavy tail is observed in the far wings of the spectrum. We also find that the PDF of the intensity in the central part of the spectrum deviates from the exponential distribution and has the dependence on the laser operating regimes, which indicates some correlations among different frequency components exist in the EYRFL radiation and may play an important role in the random lasing spectrum stabilization process.     

Amplitude fluctuations and femtosecond pulse train noise in fibers

The results of numerical investigations of the femtosecond mode-locked laser radiation spectrum broadened in an optical fiber with the effect of incoming radiation noise are presented. It was found that the pulse train intensity stability, i.e., fluctuations of incoming radiation, strongly affect output spectral characteristics such as the spectral envelope and amplitudes of equidistant components in a femtosecond comb. Thus, intensity instability of about 1–10% or less can be critical for predictable and high amplitudes of spectral components; moreover, in this case, experimental measurements of spectral envelope dissemble the real femtosecond comb amplitudes.     

Simultaneously suppressing frequency and intensity noise in a Nd:YAG nonplanar ring oscillator by means of the current-lock technique

We show that frequency and intensity noise in a Nd:YAG laser are correlated to a high degree and can be traced to the same underlying cause, namely, power fluctuations of the pump source. Because of this correlation, simultaneous suppression of frequency and intensity noise by 30 dB is achieved by means of a single actuator, the pump power.     

Polarization switching in a quasi-isotropic microchip Nd:YAG laser induced by optical feedback

This paper demonstrates the influence of external optical feedback on the polarization state of longitudinal modes in quasi-isotropic microchip Nd:YAG lasers. Under optical feedback, the polarization state of longitudinal modes in quasi-isotropic lasers relies strongly on the intracavity anisotropy loss and mode competition. When the intracavity anisotropy loss is small, external optical feedback can cause polarization switching and strong mode competition between two orthogonal linearly polarized eigenstates of one laser longitudinal mode, which leads to the distortion of laser intensity modulation waveform. The polarization switching is independent of the initial external cavity length. By increasing the intracavity anisotropy loss, one polarization eigenstate can be suppressed and the laser works in single-polarization state. A theoretical analysis based on the compound cavity model is presented, which is in good agreement with the experimental results. The results offer guidance to the development of laser feedback interferometers.     

Signal-to-noise enhancement techniques for quantum cascade absorption spectrometers employing optimal filtering and other approaches

Optical feedback to the laser source in tunable diode laser spectroscopy (TDLS) is known to create intensity modulation noise due to elatoning and optical feedback (i.e. multiplicative technical noise) that usually limits spectral signal-to-noise (S/N). The large technical noise often limits absorption spectroscopy to noise floors 100-fold greater than the Poisson shot noise limit due to fluctuations in the laser intensity. The high output powers generated from quantum cascade (QC) lasers, along with their high gain, makes these injection laser systems especially susceptible to technical noise. In this article we discuss a method of using optimal filtering to reduce technical noise. We have observed S/N enhancements ranging from ∼20% to a factor of ∼50. The degree to which optimal filtering enhances S/N depends on the similarity between the Fourier components of the technical noise and those of the signal, with lower S/N enhancements observed for more similar Fourier decompositions of the signal and technical noise. We also examine the linearity of optimal filtered spectra in both time and intensity. This was accomplished by creating a synthetic spectrum for the species being studied (CH₄, N₂O, CO₂ and H₂O in ambient air) utilizing line positions and linewidths with an assumed Voigt profile from a commercial database (HITRAN). Agreement better than 0.036% in wavenumber and 1.64% in intensity (up to a 260-fold intensity ratio employed) was observed. Our results suggest that rapid ex post facto digital optimal filtering can be used to enhance S/N for routine trace gas detection. Received: 1 April 2002 / Revised version: 7 May 2002 / Published online: 21 August 2002 RID="*" ID="*"Corresponding author. Fax: +1-509/376-6066, E-mail: robert.disselkamp@pnl.gov     

High frequency intensity noise spectra of axial mode groups in the radiation from CW GaAIAs diode lasers

The dependence of the intrinsic random intensity noise spectrum of the radiation from CW DH GaAIAs diode multimode lasers on optical wavelength has been investigated for the first time in a wide frequency range 30 MHz to 3 GHz. It was generally observed, that a lasing mode which is optically isolated from the rest of the radiation, shows much stronger intensity fluctuations as compared to the fluctuations of the total output, particularly in the frequency range below the intrinsic natural resonance frequency of the laser. The magnitude of the fluctuations decreases when the number of modes in the detected radiation increases. Our experimental results are compared to computer solutions which were obtained with a simple, analytical laser noise model. Good qualitative agreement between theory and experiment is demonstrated.     

Quantum locking of mirrors in interferometers

We show that quantum noise in very sensitive interferometric measurements such as gravitational-wave detectors can be drastically modified by quantum feedback. We present a new scheme based on active control to lock the motion of a mirror to a reference mirror at the quantum level. This simple technique allows one to reduce quantum effects of radiation pressure and to greatly enhance the sensitivity of the detection.     

Observation of sub-poisson photon statistics in the cavity-QED microlaser

We have measured the second-order correlation function of the cavity-QED microlaser output and observed a transition from photon bunching to antibunching with increasing average number of intracavity atoms. The observed correlation times and the transition from super- to sub-Poisson photon statistics can be well described by gain-loss feedback or enhanced-reduced restoring action against fluctuations in photon number in the context of a quantum microlaser theory and a photon rate equation picture. However, the theory predicts a degree of antibunching several times larger than that observed, which may indicate the inadequacy of its treatment of atomic velocity distributions.