Normalized Intensity Correlation Function Research Articles

Intrinsically Viscoelastic Supramolecular Conjugated Polymer toward Suppressing Coffee-Ring Effect

Intrinsically Viscoelastic Supramolecular Conjugated Polymer toward Suppressing Coffee-Ring Effect

Approaching single temporal mode operation in twin beams generated by pulse pumped high gain spontaneous four wave mixing.

By investigating the intensity correlation function, we study the spectral/temporal mode properties of twin beams generated by the pulse-pumped high gain spontaneous four wave mixing (SFWM) in optical fiber from both the theoretical and experimental aspects. The results show that the temporal property depends not only on the phase matching condition and the filters applied in the signal and idler fields, but also on the gain of SFWM. When the gain of SFWM is low, the spectral/temporal mode properties of the twin beams are determined by the phase matching condition and optical filtering and are usually of multi-mode nature, which leads to a value larger than 1 but distinctly smaller than 2 for the normalized intensity correlation function of individual signal/idler beam. However, when the gain of SFWM is very high, we demonstrate the normalized intensity correlation function of individual signal/idler beam approaches to 2, which is a signature of single temporal mode. This is so even if the frequencies of signal and idler fields are highly correlated so that the twin beams have multiple modes in low gain regime. We find that the reason for this behavior is the dominance of the fundamental mode over other higher order modes at high gain. Our investigation is useful for constructing high quality multi-mode squeezed and entangled states by using pulse-pumped spontaneous parametric down-conversion and SFWM.

Measurement of photon correlations with multipixel photon counters

Development of reliable photon number resolving detectors (PNRD), devices which are capable to distinguish 1,2,3.. photons, is of a great importance for quantum optics and its applications. A new class of affordable PNRD is based on multipixel photon counters (MPPC). Here we review results of experiments on using MPPCs for direct characterization of squeezed vacuum (SV) states, generated via parametric downconversion (PDC). We use MPPCs to measure the second order normalized intensity correlation function (g^(2)) and directly detect the two-mode squeezing of SV states. We also present a method of calibration of crosstalk probability in MPPCs based on g^(2) measurements of coherent states.

EFFECTS OF CORRELATION BETWEEN REAL AND IMAGINARY PARTS OF THE QUADRATIC PUMP NOISE ON THE INTENSITY FLUCTUATION OF A SINGLE-MODE LASER SYSTEM

The effects of the correlations between real and imaginary parts of the quadratic pump noise on the normalized intensity correlation function and the associated relaxation time of a single-mode laser model were investigated. The expressions of the intensity correlation function C(s) and the relaxation time Tc were derived. Based on numerical computations, we found that Tc monotonously increases as the strength λp of correlation between the real and imaginary parts of quadratic pump noise increases and the larger λp value is, the slower C(s) decays. The presence of correlations between the real and imaginary parts of the quadratic pump noise causes the intensity fluctuation to increase.

色交叉关联噪声驱动单模激光系统强度关联函数研究

Considering a single-mode laser system with cross-correlated additive colored noise and multiplicative colored noise, we study the effects of correlation among noises on the normalized intensity correlation function C(s). C(s) is derived by means of the projection operator method. The effects of the self-correlation time tau1 of the additive colored noise, tau2 of the multiplicative colored noise, and the effect of the cross-correlation time tau0 between the two noises on C(s) are discussed by numerical calculation. For the case of positive correlation (\lambdag0), it is found that when a0g0 the normalized intensity correlation function C(s) increases with the increase of tau0 or tau2, and with value of tau0 or tau2 becoming larger, C(s) comes to saturation. With increasing the self-correlation time tau1 of the additive noise, a minimum and a maximum will appear on curve of C(a) as a0g0. If a0l0, C(s) decreases with the increase of tau0, tau1, and tau2.

Dynamic correlation in wave propagation in random media.

Field spectra are analyzed to yield the time-resolved statistics of pulsed transmission through quasi-one-dimensional dielectric media with static disorder. The normalized intensity correlation function with displacement and polarization rotation for an incident pulse of linewidth sigma at delay time t is a function only of the field correlation function, which is identical to that found for steady-state excitation, and of kappa(sigma)(t), the residual degree of intensity correlation at points at which the field correlation function vanishes. The dynamic probability distribution of normalized intensity depends only upon kappa(sigma)(t). Steady-state statistics are recovered in the limit sigma-->0, in which kappa(sigma=0) is the steady-state degree of correlation.

Effects of correlated noises on the intensity fluctuation of a single-mode laser system

We consider a single-mode laser model with cross-correlated additive and multiplicative noises term, and study the effects of correlation between noises on the normalized intensity correlation function C( τ) and the associated relaxation time T c by means of projection operator method, in which the effects of the memory kernels of the correlation function are taken into account. Based on numerical computations it is found that nearby threshold the presence of negatively correlated noises slows down the decay of fluctuation, whereas presence of positively correlated noises speed up the decay of fluctuation. Far apart from threshold the influence of correlation between noises on T c are very weak. In addition we analyze the influence of the memory on the T c and C( τ). The influence of the memory slows up the decay of the intensity correlation function.

Correlation measurements in resonance fluorescence with spectral resolution and atomic inversion via detection of a spectrally filtered photon

We consider a special kind of correlation measurements in single-atom resonance fluorescence, which includes detection of a spectrally filtered photon followed by detection of an unfiltered photon. We relate the stationary normalized intensity correlation function measured in such a scheme to the reduced atomic state following detection of the filtered photon. In the limit of well separated spectral lines of the resonance fluorescence spectrum, we obtain the analytic expression for the reduced atomic state. We show that at resonance excitation, this state is inverted when the filter is tuned in between the central line and any of the sidebands. This effect is interpreted as a result of quantum interference between the complementary atomic radiative transitions giving rise to the detected photon. We propose to observe this effect in measuring the equal-time field correlation function of the filtered and unfiltered photons as a function of the filter resonance frequency.

Dynamical properties of a laser with correlations between additive and multiplicative noise

The dynamical properties of a single-mode laser with correlations between additive and multiplicative white-noise terms are investigated theoretically. The normalized intensity correlation function, the correlation time and the effective eigenvalues are calculated through a one-dimensional laser equation. Compared with a laser model of independent noise terms, the coupling between noise terms slows down the decay of intensity correlations in the laser field.

Spontaneous emission from two atoms interacting with a broadband squeezed vacuum.

Spontaneous emission from two-level atoms interacting with a squeezed vacuum field is examined, taking account of possible different interatomic separations. It is shown that the steady-state atomic population depends on whether the interatomic separations are comparable to or much smaller than the resonant wavelength. For the extended system the squeezed vacuum introduces a dependence of the atomic population on the interatomic separations. For large interatomic separations the atomic population is identical to that for the thermal field, which is the same for two independent atoms. For small interatomic separations the atomic population is higher than that for the thermal field. This is in contrast to the small-sample model in which the interatomic separation is ignored. In this case the final atomic population in the squeezed vacuum is the same as that for the independent atoms in the squeezed vacuum. Moreover, this population differs from that for the thermal field for which the atomic population is lower than that for the independent atoms. This difference is due to the interatomic correlations whose presence depends on whether the interatomic separation is or is not included. For the extended system the interatomic correlations are induced by the squeezed field and vanish for the thermal field. For the small-sample model, however, the interatomic correlations are induced by the thermal field and the squeezed vacuum changes these correlations in such a way that for the minimum-uncertainty squeezed states these correlations vanish. We also discuss the effect of the interatomic separation on the two-photon transitions and the normalized intensity correlation function in the two-atom system interacting with the squeezed vacuum field.

Intensity dependence of the normalized intensity correlation function in parametric down-conversion

The question under what conditions a normalized intensity correlation function λ 12(τ) depends strongly on the average light intensity is discussed. It is shown that in the process of spontaneous parametric down-conversion the strong correlation between signal and idler photons makes λ 12(τ) inversely proportional to the light intensity of either the signal or idler beam. This conclusion is then confirmed experimentally by two-time photoelectric correlation measurements.

Level-Crossing Detection By Photon Statistics

In this paper several level-crossing detection techniques based on photon statistics are presented. Results on level-crossing detection through the measurement of the normalized second-order factorial moment n(2)(T) are reviewed. Detection by measurement of the normalized intensity correlation function g(2)(r) or the Laplace transform of time-interval probability is studied. The interest of the above mentioned techniques is analyzed.

Theory of Resonance Fluorescence from Vibronic Systems

The problem of resonant interaction between an electromagnetic radiation field and a vibronic system, such as a molecule or a localized electronphonon system, is considered. The vibronic coupling is assumed to result from displaced and distorted potential energy surfaces for the vibrational motion in the electronic quantum states involved in the resonant interaction with the radiation field. Furthermore, the vibrational energy relaxation is taken into account without assumptions about Markovian-type relaxation. In order to study correlation properties of higher than second order in the electric field strength of the light emitted a method of calculation of the expectation value of an arbitrary product combination of effective time evolution operators of the vibronic system is developed. The calculations are performed by utilizing Feynman's disentangling and operator ordering techniques and yield closed solutions in the low-temperature limit. The theory is used for studying the intensity and the normally ordered intensity correlation function of the resonance fluorescence light from a two-atom molecule excited by a relatively weak laser field, which undergoes phase fluctuations.It is shown that the vibronic coupling can give rise to an anticorrelation effect which is substantially stronger than in the case of resonance fluorescence from an atom. For the case of small vibrational damping a general formula which directly connects the asymptotic long-time behaviour of the normalized intensity correlation function with the vibrational relaxation in the molecule is deduced. It should be convenient for the determination of very small vibrational decay rates.

Effect of spatial incoherence of the laser in photon-correlation spectroscopy

The effects of spatial incoherence of the laser output in photon-correlation spectroscopy are examined both theoretically and experimentally. It is shown that, when several transverse cavity modes oscillate simultaneously at different frequencies, the amplitude of fluctuations in the intensity of scattered light can be reduced significantly. For simultaneous operation of TEM00 and TEM01* (doughnut) modes the reduction of the zero-time-delay intercept g(2)(0) − 1 [where g(2)(τ) is the normalized intensity-correlation function] can amount to a factor of 3. The effects are shown to be particularly marked when high-gain ion lasers are used, and hitherto unexplained apparently random changes of intercept have been found. Possible implications of these observations for speckle applications, holography, and other forms of coherent optical processing are pointed out.