Techniques for Spectroscopy with Frequency Combs

[摘要] This dissertation contains several novel works pertaining to the use of frequency combs for spectroscopy.First, the optimum comb repetition rates (f_Sig and f_LO) for dual-comb spectroscopy were determined using a Monte Carlo approach to quantify their impact on the standard deviation of the error, sigma, of the fitted parameters of a single Lorentzian resonance (assuming all else is equal, i.e. lasers powers, acquisition time, etc.). A maximum allowable spectral point spacing, delta_nu of about gamma, where gamma is the half width at half maximum of the resonance was identified. For the traditional implementation of dual-comb spectroscopy, the ideal repetition rates are f_Sig is about f_LO is about gamma but even more accurate measurements can be made by allowing for arbitrary near-harmonic repetition rate ratios. In this case the ideal repetition rates are f_Sig less than or equal to gamma and f_LO goes to infinity. In general, sigma is proportional to the inverse square root of f_LO (i.e. no f_Sig dependence) for f_Sig less than or equal to gamma. The simulations were then generalized to quantify how the signal-to-noise ratio (SNR) and spectral point spacing, delta_nu, affect the error, sigma, in the fitted parameters of a Lorentzian function. The general result, sigma is proportional to delta_nu to the one half power all divided by the SNR, was identified which applies beyond spectroscopy to any peak fitting situation.Second, a novel type of frequency comb source based on a single-section semiconductor diode laser was characterized and its potential to enable battery-powered dual-comb spectroscopy was examined. For characterization, the tunability of the comb parameters (i.e. the repetition rate and offset frequency) was measured as a function of the diode temperature and injection current. Tuning the injection current (temperature) was found to change the repetition rate by -91 +/- 9 MHz/A (-2 +/- 3 MHz/K) and the offset frequency by -4.2 +/- 0.1 kHz/A (-4.4 +/- 0.2 kHz/K). Next, the ability to perform dual-comb spectroscopy using these combs powered by standard laboratory-grade equipment was demonstrated. Later, a battery-powered current driver was built that successfully powered a comb.Third, a novel form of nonlinear hyperspectral imaging that leveraged frequency combs was developed and demonstrated. 400-pixel images that spectrally resolved a four-wave mixing signal from a GaAs-quantum-well-based sample with comb resolution were constructed using only 45 seconds worth of collected data. The images reveal spatially varying spectral features that can be attributed to a combination of an inhomogeneous, thermally-induced strain field and the quantum confined Stark effect it produces via a piezoelectric field. Advantages of this technique compared to prior arts were also evaluated.Fourth, a novel technique coined tri-comb spectroscopy that replaces the mechanical delay lines used in many multi-dimensional coherent spectroscopy experiments with three frequency combs having different repetition rates was developed and demonstrated. A rephasing spectrum and multiple linear spectra, all with comb resolution, of a gaseous mixture of Rb isotopes were simultaneously constructed from only 365 ms of acquired data. Future improvements to this technique where the repetition rates of all combs are identical were posited and explored.

[发布机构] University of Michigan

[效力级别] Spectroscopy

[关键词] Frequency comb;Spectroscopy;Physics;Science;Applied Physics