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Journal of the Optical Society of America A

Continuous manipulation of tunable mixed classical light from coherent light to pseudothermal light

Hee Jung Lee, In‐Ho Bae, Han Seb Moon

Published Mar 10, 2011• 2 citations
Publisher

Abstract

We demonstrated tunable mixed classical light (TMCL) using a mixture of a laser and a pseudothermal light. The TMCL was generated by adjusting the photon number ratio of a laser and a pseudothermal light. The photon number statistics of the TMCL continuously changed from the Poisson distribution to the Bose-Einstein distribution. The g((2)) (0) value of the TMCL was measured using the Hanbury Brown-Twiss method, and we could arbitrarily control the g((2)) (0) value between 1.0 and 1.7. The experimental g((2)) (0) value of the TMCL as a function of the photon number ratio of the two light sources was in close agreement with the calculated result.

DOI
10.1364/josaa.28.000560

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We demonstrated tunable mixed classical light (TMCL) using a mixture of a laser and a pseudothermal light. The TMCL was generated by adjusting the photon number ratio of a laser and a pseudothermal light. The photon number statistics of the TMCL continuously changed from the Poisson distribution to the Bose-Einstein distribution. The g((2)) (0) value of the TMCL was measured using the Hanbury Brown-Twiss method, and we could arbitrarily control the g((2)) (0) value between 1.0 and 1.7. The experimental g((2)) (0) value of the TMCL as a function of the photon number ratio of the two light sources was in close agreement with the calculated result.
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The advent of controlled experimental accessibility of Bose-Einstein condensates, as realized with e.g. cold atomic gases, exciton-polaritons, and more recently photons in a dye-filled optical microcavity, has paved the way for new studies and tests of a plethora of fundamental concepts in quantum physics. We here describe recent experiments studying a transition between laser-like dynamics and Bose-Einstein condensation of photons in the dye microcavity system. Further, measurements of the second-order coherence of the photon condensate are presented. In the condensed state we observe photon number fluctuations of order of the total particle number, as understood from effective particle exchange with the photo-excitable dye molecules. The observed intensity fluctuation properties give evidence for Bose-Einstein condensation occurring in the grand-canonical statistical ensemble regime.
We describe photon statistics experiments using pseudothermal light that can be performed in an undergraduate physics laboratory. We examine the light properties in terms of a second-order coherence function, as determined either by measuring the light intensity as a function of time or via coincidence analysis of a pair of photon detectors. We determine the coherence time and intensity distribution of the pseudothermal light source that exhibits either Gaussian or non-Gaussian statistics as a function of their optical parameters, and then compare the results with theoretical predictions. The simple photodiode method can be used for the qualitative analysis of the coherence time, but more accurate measurements are achieved using the coincidence method.
It is well known that the reduced state of a two-mode squeezed vacuum state is a thermal state, i.e., a state whose photon-number statistics obey a geometric distribution. More exotic broadband states can be realized as the reduced state of two spectrally entangled beams generated using nonlinear optics. We show that these broadband ``pseudothermal'' states are tensor products of states in spectral Schmidt modes, whose photon-number statistics obey a geometric distribution. We study the spectral and temporal coherence properties of these states and show that their spectral coherence can be tuned---from perfect coherence to complete incoherence---by adjusting the pump spectral width. In the limit of a cw pump, these states are tensor products of true thermal states but with different temperatures at each frequency. This could be an interesting state of light for investigating the interplay between spectral, temporal, and photon-number coherences.
Correlation property of light limits the performance in related applications such as the visibility of ghost imaging or intensity interferometry. To exceed these performance limits, we here manipulate the degree of second- and higher-order coherence of light by changing controllable variables in four-wave mixing (FWM) process. The measured degree of second- and third-order coherence of the output light beams considerably exceed those of the incident pseudothermal light. Namely superbunching effects, g(2)(0) value up to 7.47 and g(3)(0) value up to 58.34, are observed experimentally. In addition, strong second- and third-order cross-correlation exist between the output light beams. Further insights into the dependence of superbunching light on the temperature of Rb vapor, the laser detuning and the optical power of all the incident light beams show that it can serve as a light source with a tunable superbunching degree.