Transient first-order interference of two independent thermal light beams

Abstract

By analyzing the first-order interference of two independent thermal light beams with both classical and quantum theories, we conclude that it is impossible to observe the transient first-order interference pattern by superposing two independent thermal light beams even if the degeneracy parameter of thermal light is much greater than one. The result suggests that the classical model of thermal light field within the coherence time may not be the same as the one of laser light field within the coherence time.Shortly after the invention of laser [1], the first-order interference of two independent laser light beams was reported [2][3][4]. Magyar and Mandel observed spatial transient first-order interference pattern by superposing two independent ruby laser light beams [3]. Transient firstorder interference pattern is the first-order interference pattern obtained in a short time interval, which is usually shorter than the coherence time of the field. Further more, Pfleegor and Mandel proved that the interference of two independent laser light beams takes place even under conditions in which "the intensities are so low that, with high probability, one photon is absorbed before the next one is emitted by one or the other source" [5]. Forrester et al. observed beats by mixing Zeeman components of a visible spectral line [6]. However, their experiment can not be regarded as the interference of two independent thermal light beams. For the interfering fields in their experiment have common origin, which is similar as the latter experiments of interference of light emitted by two sources [7][8][9][10][11]. The transient first-order interference of two independent thermal light beams like the one with two independent laser light beams [2-4] has never been reported. Most physicists attribute it to that the degeneracy parameter of thermal light is usually much less than one [12,13]. On the other hand, if the degeneracy parameter of thermal light is much greater than one, the transient first-order interference pattern of two independent thermal light beams can be observed. Is this prediction true? Our answer is no. In the following part, we will show that it is impossible to observe the transient first-order interference pattern by superposing two independent thermal light beams even if the degeneracy parameter of thermal light is much greater than one. Our results suggest that thermal and laser light fields are different within the coherence time.Thermal light is usually obtained by passing blackbody radiation through linear filters, such as apertures, mirrors, lenses, polarizers, etc [14]. It is also sometimes called chaotic light. Gas discharge lamp is one of the typical thermal light sources, where the different * liujianbin@mail.xjtu.edu.cn excited atoms emit their radiation independently of one another. The total thermal light field equals the sum of all these randomly and independently emitted radiation fields. For example, let us follow Loudon's book to discuss the temporal fluctuation of polarized thermal light emit...