Abstract
Recent developments in optical metrology have tremendously improved the precision and accuracy of the horizontal (frequency) axis in measured spectra. However, the vertical (typically absorbance) axis is usually based on intensity measurements that are subject to instrumental errors which limit the spectrum accuracy. Here we report a one-dimensional spectroscopy that uses only the measured frequencies of high-finesse cavity modes to provide complete information about the dispersive properties of the spectrum. Because this technique depends solely on the measurement of frequencies or their differences, it is insensitive to systematic errors in the detection of light intensity and has the potential to become the most accurate of all absorptive and dispersive spectroscopic methods. The experimental results are compared to measurements by two other high-precision cavity-enhanced spectroscopy methods. We expect that the proposed technique will have significant impact in fields such as fundamental physics, gas metrology and environmental remote sensing.
Highlights
Spectroscopy is a powerful measurement tool that can provide deep insight into the physics governing the microscopic world
It demonstrates the sub-Hz precision of measurements of the cavity mode widths and the position resolution achieved in our experiment
We found that the main contribution to the statistical noise of the cavity mode width and position comes from the quality of the lock between the laser and cavity
Summary
Spectroscopy is a powerful measurement tool that can provide deep insight into the physics governing the microscopic world. An electromagnetic wave propagating in an absorbing medium experiences attenuation of its amplitude and shift of its phase. These mechanisms, which are ascribed to absorption and dispersion respectively, are interrelated in case of linear response limit by the familiar KramersKronig equations [7]. Both effects can be used to quantify the amount of substance, absorption measurements are more common than those of phase, which are generally more experimentally demanding. In the vicinity of an absorbing (amplifying) medium placed inside a high-finesse optical cavity, absorption and dispersion effects cause characteristic cavity mode broadening (narrowing) and pushing (pulling) relative to the absorption peak
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