Null polarimetry near shot noise limit at 1 Hz

Abstract

We describe the principle and report on the realization of a null polarimeter with two demonstrated features: (1) the sensitivity of the system is near shot noise limit and (2) quasi-stationary signals at 1 Hz can be measured without signal modulation. The achieved single-pass sensitivity is 7 × 10(-9) rad/Hz with a pair of Glan-Taylor polarizers, which should be of great interest for experiments such as observation of vacuum magnetic birefringence and search for new particles. The system is brought near its shot noise limit by appropriate polarization control and coherent heterodyne detection of light, resulting in a sensitivity improvement by two orders of magnitude in comparison with the case of no control on light polarization.

A model independent study of nonlocality with polarization entangled photons

“…After the 0.3 ms period of time, the light source is turned off so that the wave plates may freely rotate for say τ = 100 s during which time the relative angle of the two plates will change by of the order of θ = ∆ω p τ ≈ 0.01 • . The magnitude of θ is within the detection capability of a null polarimeter near shot noise limit [35].…”

Noise reduction and signal to noise ratio improvement in magneto-optical polarization rotation measurement

“…The typical applications involving the measurement of Faraday rotation include highly sensitive atomic magnetometers [1,3,5] , atomic sensors [6,7] , experiments on fundamental physics [2,4] , optical isolators [8] , optical modulators [9] , magnetic field, and current sensor [10][11][12] . Different polarimetry techniques have been demonstrated to measure the Faraday rotation with and without any modulation [2,4,[12][13][14][15][16][17][18][19][20] . The simplest polarimeter requires two linear polarizers, a laser light source, and a photodetector (PD).…”

“…The rotation angle is determined by using Malus law [19] . For a polarimeter without involving any modulation, the sensitivity is generally limited by the extinction ratio of polarizers used [14] . The extinction ratio of typical birefringent polarizers is 1 × 10 −6 .…”

“…The use of modulation techniques allows one to measure the Faraday rotation with enhanced sensitivity by suppressing the noises and without requiring polarizers with the highest extinction ratio [14] . The desired signal is extracted at a particular modulation frequency, while signals at other frequencies are suppressed electronically.…”

“…The outputs of two PDs given by Eqs. (14) and (15) can be combined differentially. Assuming that the gain of both the detectors is same, the first harmonics extracted by the lockin amplifier referenced at the modulation frequency are given by…”