The second-order interference between laser and thermal light

Abstract

Two-photon anticorrelation is observed when laser and pseudothermal light beams are incident to the two input ports of a Hong-Ou-Mandel interferometer, respectively. The spatial second-order interference pattern of laser and pseudothermal light beams is reported. Temporal Hong-Ou-Mandel dip is also observed when these two detectors are at the symmetrical positions. These results are helpful to understand the physics behind the second-order interference of light.Ever since the second-order interference of light was first observed by Hanbury Brown and Twiss (HBT) in 1956 [1], it has been an important tool to study the properties of light [2]. The second-order interference of light has been studied with photons emitted by different kinds of sources, such as entangled photon pair source [3], two independent single-photon sources [4][5][6], laser and single-photon source [7], laser and entangled photon pair source [8], two lasers [9][10][11], two thermal sources [12][13][14][15][16][17], etc. Many interesting results were obtained from those studies. For instance, Hong et al. were able to measure the time separation between two photons with time resolution millions of times shorter than the resolution of the detector and the electronics [3,18]. Pittman et al. got the ghost image of an object with entangled photon pairs [19]. Bennett et al. observed Hong-Ou-Mandel (HOM) dip by feeding photons emitted by single-photon source and laser into the two input ports of a HOM interferometer, respectively [7]. The second-order interference of photons coming from laser and thermal light beams seems to have not been studied, in which, something interesting may happen. In this letter, we will experimentally study the second-order interference of laser and pseudothermal light beams in a HOM interferometer, where two-photon anticorrelation and temporal HOM dip are observed when these two detectors are at the symmetrical positions.Two-photon anticorrelation is defined as the twophoton coincidence count probability is less than the accidental two-photon coincidence count probability, which is equal to the product of these two single-photon probabilities [20]. It is convenient to employ the normalized second-order coherence function or the degree of secondorder coherence [21], g (2) (r 1 , t 1 ; r 2 , t 2 ) = G (2) (r 1 , t 1 ; r 2 , t 2 )to discuss the second-order correlation of light. Where G (2) (r 1 , t 1 ; r 2 , t 2 ) is the second-order coherence function at space-time coordinates (r 1 , t 1 ) and (r 2 , t 2 ). G(1) (r 1 , t 1 ) and G (1) (r 2 , t 2 ) are the first-order coherence functions at (r 1 , t 1 ) and (r 2 , t 2 ), respectively [22]. When g (2) (r 1 , t 1 ; r 2 , t 2 ) is greater than 1, these two photon detection events are correlated. When g (2) (r 1 , t 1 ; r 2 , t 2 ) is equal to 1, these two events are independent. When g (2) (r 1 , t 1 ; r 2 , t 2 ) is less than 1, these two events are anticorrelated. In our experiments, we are able to observe two-photon anticorrelation when these two single-photon detection event...

Superbunching pseudothermal light

“…If a single-mode continuous-wave laser light beam is employed as the input before P 1 in Fig. 1, the scattered light after RG 1 is pseudothermal light [38], which has been applied extensively in thermal light ghost imaging [39][40][41][42], the second-and higher-order interference of thermal light [43][44][45][46]. The photons in light beam after N (N ≥ 2) RGs will be superbunched, which means the normalized second-order coherence function, g (2) (0), will exceed 2.…”

Studying fermionic ghost imaging with independent photons

“…In fact, Feynman himself had also employed this method to interpret two-photon bunching effect in one of his lectures [42]. Recently, we have employed the same method to discuss the second-order interference of two independent light beams [43][44][45][46], which greatly simplifies the calculation and offers a better understanding about the relation between the mathematical calculations and physical interpretations. We will also employ the same method to calculate ghost imaging with thermal fermions.…”

“…There are two different alternatives for the particles emitted by thermal source S to trigger a two-particle coincidence count at D 1 and D 2 [41][42][43][44][45][46], which is equivalent to a Hanbury Brown-Twiss (HBT) interferometer [38,39]. One is particle a goes to D 1 and particle b goes to D 2 .…”

Space-Time Quantum Imaging

“…Martienssen and Spiller characterized the time varying effect of ground glass on coherent radiation. In fact, ground glass is currently being used in fundamental experiments on studying the quantum superposition of coherent and pseudo-thermal light [11]. In the following we introduce a new model for ground glass that incorporates both time and space phase disturbance effects into the ghost imaging process.…”

“…Other interesting Ghost imaging research includes experiments on entangled photon ghost imaging through laboratory turbulence [3], signal-to-noise studies and illumination variations [4,5], studies on contrast and visibility [6,7], virtual or computational ghost imaging [8][9][10], along with associated fundamental experimental [11] and theoretical physics [12][13][14]. Extending the remote ghost imaging practical application to a turbulent environment, Turbulence-free Ghost Imaging (Meyers et al [15,16]) was recently proven, wherein turbulence has virtually no adverse effect on ghost imaging as shown in Figure 1.…”