Abstract
We have demonstrated experimentally a Diode-Pumped Alkali Laser (DPAL) with a Raman resonance induced dip in the center of the gain profile, in order to produce an anomalous dispersion, necessary for making the laser superluminal. Numerical calculations match closely with experimental results, and indicate that the laser is operating superluminally, with the group index far below unity (~0.00526) at the center of the dip. The estimated factor of enhancement in the sensitivity to cavity length perturbation is ~190, approximately equaling the inverse of the group index. This enhancement factor can be made much higher via optimal tuning of parameters. Such a laser has the potential to advance significantly the field of high-precision metrology, with applications such as vibrometry, accelerometry, and rotation sensing.
Highlights
Optical interferometry is currently the standard technique for making many of the most precise measurements, but there still exist many applications for which even the best interferometers are not sensitive enough, and some applications for which higher sensitivity will always be of interest
Over the last few years, significant effort has been underway towards theoretical understanding and experimental realization of superluminal lasers, with the ultimate goal of metrological sensitivity enhancement [1,2,3,4,5,6,7,8,9,10,11]
It has been shown that the sensitivity of a ring laser with respect to cavity length perturbation is inversely proportional to the group index of the material inside the cavity [3,8]
Summary
Optical interferometry is currently the standard technique for making many of the most precise measurements, but there still exist many applications for which even the best interferometers are not sensitive enough, and some applications for which higher sensitivity will always be of interest. With properly-tuned parameters, ng−1 can exceed 105 over a significant bandwidth, leading to sensitivity enhancement of more than five orders of magnitude This is calculated and described in detail in [9]. The process starts by creating a ring laser for which gain is provided by an optically-pumped Rubidium vapor cell containing a highpressure buffer gas [12]. Another vapor cell (without buffer gas) is placed inside the cavity and is optically pumped so that population imbalance between the two hyperfine ground states is achieved This leads to gain in the Raman probe, accompanied by depletion of the intra-cavity beam, which effectively serves as the Raman pump in this process. With an analytic expression for χR (ν ) , an analytic expression for R is obtainable using Eq (3)
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