Abstract
We measure the frequency noise across a Cr:forsterite infrared frequency comb through the optical heterodyne beat of different comb teeth against stable continuous wave (CW) lasers. This sensitive measurement shows strong correlations of the frequency noise between spectral components of the comb, relative to a fixed optical frequency near the 1.3 micron carrier of the Cr:forsterite laser. The correlated frequency fluctuations are shown to arise from amplitude noise on the pump laser. We also report a preliminary comparison of excess noise that occurs during supercontinuum generation in both highly nonlinear fiber and an extruded glass microstructured fiber.
Highlights
Supercontinuum generation with low power mode-locked femtosecond lasers and highly nonlinear optical fibers has provided optical frequency combs that are used in a variety of high precision frequency metrology and spectroscopy applications [1, 2]
With the sensitive optical heterodyne technique, we explore the strong correlations between the frequency noise on the same sides of spectrum relative to this fixed point [4, 7, 8, 9]
We see evidence that there is additional frequency noise arising in the process of supercontinuum generation and that it depends on the specific nonlinear fiber
Summary
Supercontinuum generation with low power mode-locked femtosecond lasers and highly nonlinear optical fibers has provided optical frequency combs that are used in a variety of high precision frequency metrology and spectroscopy applications [1, 2]. We analyze the frequency noise on an infrared frequency comb generated with a Cr:forsterite femtosecond laser. As illustrated here one can gain a factor of ∼ 106 in sensitivity by instead measuring the frequency noise of the optical comb components. We employ this approach with heterodyne measurements between specific comb teeth and CW lasers at different wavelengths across several hundred nanometers in the 1-2 micron range. For our Cr:forsterite laser, the frequency fluctuations are caused primarily by the amplitude noise on the pump laser, which drives a breathing motion of the comb about a central fixed point near 1.3 microns. We see evidence that there is additional frequency noise arising in the process of supercontinuum generation and that it depends on the specific nonlinear fiber
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