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arXiv:0809.3913 · Optics Express

Fast-light in a photorefractive crystal for gravitational wave detection

H. Yum, M. Salit, G. S. Pati, S. Tseng, Philip Hemmer, M. S. Shahriar

Published Nov 25, 2008• 35 citations
arXivHTMLPDF

Abstract

We demonstrate superluminal light propagation using two frequency multiplexed pump beams to produce a gain doublet in a photorefractive crystal of Ce:BaTiO(3). The two gain lines are obtained by two-wave mixing between a probe field and two individual pump fields. The angular frequencies of the pumps are symmetrically tuned from the frequency of the probe. The frequency difference between the pumps corresponds to the separation of the two gain lines; as it increases, the crystal gradually converts from normal dispersion without detuning to an anomalously dispersive medium. The time advance is measured as 0.28 sec for a pulse propagating through a medium with a 2 Hz gain separation, compared to the same pulse propagating through empty space. We also demonstrate directly anomalous dispersion profile using a modified experimental configuration. Finally, we discuss how anomalous dispersion produced this way in a faster photorefractive crystal (such as SPS: Sn(2)P(2)S(6)) could be employed to enhance the sensitivity-bandwidth product of a LIGO type gravitational wave detector augmented by a White Light Cavity.

DOI
10.1364/oe.16.020448

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Physica Scripta•Apr 1, 2014•1 citation
We demonstrate superluminal light propagation using two frequency multiplexed pump beams to produce a gain doublet in a photorefractive crystal of Ce:BaTiO(3). The two gain lines are obtained by two-wave mixing between a probe field and two individual pump fields. The angular frequencies of the pumps are symmetrically tuned from the frequency of the probe. The frequency difference between the pumps corresponds to the separation of the two gain lines; as it increases, the crystal gradually converts from normal dispersion without detuning to an anomalously dispersive medium. The time advance is measured as 0.28 sec for a pulse propagating through a medium with a 2 Hz gain separation, compared to the same pulse propagating through empty space. We also demonstrate directly anomalous dispersion profile using a modified experimental configuration. Finally, we discuss how anomalous dispersion produced this way in a faster photorefractive crystal (such as SPS: Sn(2)P(2)S(6)) could be employed to enhance the sensitivity-bandwidth product of a LIGO type gravitational wave detector augmented by a White Light Cavity.
We demonstrate slow and fast light at room temperature by dispersive phase-coupling in a photorefractive SBN:60 crystal. Non-degenerated wave-mixing is used to obtain delayed and amplified pulses with reduced or increased group velocity of vg = 0. 2c m s −1 and vg =− 1. 3c m s −1 , respectively. The gain spectrum is modulated by using multiple frequency shifted pumps simultaneously. The complete dispersion of the spectrum is determined via the phase modulation technique. We compare the experimental results to numerical simulations based on coupled-wave equations.
We demonstrated superluminal light propagation with a negative group velocity of -5.7 m/s in a photorefractive Bi 12SiO20 crystal by using the dispersive phase coupling effect in a nondegenerate two-wave mixing process. To the best of our knowledge, this is the first experimental demonstration of superluminal light propagation at room temperature in solids by using a classical wave mixing technique. In addition, we showed the tunability of the group velocity of light between the negative (superluminal light) and the positive (subluminal light) by simply tuning the experimental conditions such as the frequency of the coupling beam, the incident intensity, and the externally applied electric fields.
A superluminal ring laser (SRL) is a laser in which the group velocity of light far exceeds, by a factor as large as a million, the vacuum speed of light, without violating special relativity or causality. This behavior results from the so-called fast light effect, corresponding to critically tuned anomalous dispersion. The anomalous dispersion is produced by adding inside the ring cavity an auxiliary medium that produces a narrow dip in the broad-band gain profile produced by the main gain medium. In an SRL, the change in the laser frequency, as a function of a change in the cavity length, is enhanced by a factor of nearly a million, when compared to that of a conventional ring laser. This effect can be used for enhancing the sensitivity of many devices, including a gyroscope, and accelerometer, and a fiber optic sensor. It can also be configured to realize a novel type of gravitational wave detector. We have realized an SRL using a buffer gas loaded Rb vapor cell, pumped on the D1 line, as the main gain medium, and an additional Rb vapor cell for producing the anomalous dispersion via Raman induced pump depletion. In this talk, the author will describe the behavior of this SRL, and outline the various applications we are pursuing, including rotation sensing and accelerometry for inertial navigation under GPS-denied conditions, and gravitational wave detection. He will also describe a fiber-optic based SRL, employing dual peaked Brillouin gain, for ultra-sensitive, general purpose fiber optic sensing.
Slow and fast light are achieved in two experiments using SPS photorefractive crystal at room temperature. We report that the photorefractive gain achieved by the two wave mixing (TWM) method can control the group velocity of the transmitted light pulses at visible wavelength. It is shown theoretically and experimentally that the time delay and the shape of the output pulse change as a function of the photorefractive gain. The beam fanning has also been used to control the velocity propagation of a single light pulse in the same crystal at λ = 1064 nm. Depending on the orientation of the polar axis, it is possible to accelerate or decelerate a short pulse with duration of order of μs in the crystal.
Techniques to control dispersion in a medium have attracted much attention due\nto potential applications to devices such as ring laser gyroscopes, interferometric\ngravitational wave detectors, data buffers, phased array radars and quantum information\nprocessors. Of particular interest is an optical resonator containing a medium with an\nanomalous dispersion corresponding to fast-light, which behaves as a White Light\nCavity (WLC). A WLC can be tailored to improve the sensitivity of sensing devices as\nwell as to realize an optical data buffering system that overcomes the delay-bandwidth\nproduct of a conventional cavity.\nThis dissertation describes techniques to tailor the dispersion for fast-light in\nintracavity media. We present first a demonstration of fast-light in a photorefractive\ncrystal. When placed inside a cavity, such a medium could be used to enhance the\nbandwidth of a gravitational wave detector. We then describe how a superluminal laser\ncan be realized by adding anomalously dispersive medium inside a ring laser. We\nidentify theoretical conditions under which the sensitivity of the resonance frequency to a change in the cavity length is enhanced by as much as seven orders of magnitude. This\npaves the way for realizing a fast-light enhanced ring laser gyroscope, for example. This\nis followed by the development of a novel data buffering system which employs two\nWLC systems in series. In this system, a data pulse can be delayed an arbitrary amount\nof time, without significant distortion. The delay time is independent of the data\nbandwidth, and is limited only by the attenuation experienced by the data pulse as it\nbounces between two high-reflectivity mirrors. Such a device would represent a\nsignificant breakthrough in overcoming the delay-time bandwidth product limitation\ninherent in conventional data buffers.\nWe then describe our experimental effort to create a fiber-based WLC by using\nstimulated Brillouin scattering (SBS). Experimental results, in agreement with our\ntheoretical model presented here, show that the WLC effect is small under the conditions\nsupported by current fiber optic technology. We conclude that future efforts to induce a\nlarge WLC effect would require fibers with high Brillouin coefficient and low\ntransmission loss, as well as optical elements with very low insertion loss and high\npower damage thresholds.
We analyse the propagation of a probe laser pulse though a medium of atoms in the double Λ configuration with two closely spaced upper levels. The medium is irradiated with a strong coherent field and is additionally incoherently pumped. Depending on the parameters of the system the dispersion of the medium may change alternatively from normal to anomalous with absorption varying from positive to negative (gain). The incoherent optical pump was found to be the switch between the sub- and the superluminal regime. A laser field propagating through such an optical system can experience alternatively the negative or positive group velocity. The dynamics of propagation in the case of positive but larger than c group velocities is investigated in particular. In this paper we show how the description in terms of the group velocity breaks down in the superluminal regime.