ABSTRACT
As an extension of the ideas of Hanbury-Brown and Twiss, a method is proposed to eliminate the phase noise of white chaotic light in the regime where it is dominant, and to measure the much smaller Poisson fluctuations from which the incoming flux can be reconstructed. The best effect is achieved when the timing resolution is finer than the inverse bandwidth of the spectral filter. There may be applications to radio astronomy at the phase noise dominated frequencies of 1–10 GHz, in terms of potentially increasing the sensitivity of telescopes by an order of magnitude.
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Footnotes
- 3
The assumption of a 50:50 beam splitter is actually inessential to the arguments and conclusion of this paper.
- 4
The quantity 1/n0 in (35) should strictly speaking be 1/n0 + 1/n'0, where n0 and n'0 ≫ n0 are, respectively, the number of photons in the radiation of the source and background (including the thermal noise of the amplifier) before and after amplification. To elaborate, the 1/n'0 term should be there even if it is totally negligible, as this paper is primarily about the amplified radiation. But the floor of η in Equation (35) should be set by 1/n0, which gives the intrinsic shot noise before the signal is amplified. Looking from another viewpoint, due to intrinsic fluctuations the amplified radiation cannot be taken as steady on timescales corresponding to such small values of x that all the x-dependent terms of η have become insignificant.