Abstract
Femtosecond lasers allow for simultaneous detection of multiple absorption lines of a specimen over a broad spectral range of infrared or visible light with a single spectroscopic measurement. Here, we present an 8-THz bandwidth, 0.5-GHz resolution scheme of Fourier-transform spectroscopy using an Er-doped fiber femtosecond laser. A resolving power of 1.6 × 104 about a 1560-nm center wavelength is achieved by sweeping the pulse repetition rate of the light source on a fiber Mach-Zehnder interferometer configured to capture interferograms with a 0.02-fs temporal sampling accuracy through a well-stabilized 60-m unbalance arm length. A dual-servo mechanism is realized by combining a mechanical linear stage with an electro-optic modulator (EOM) within the fiber laser cavity, enabling stable sweeping control of the pulse repetition rate over a 1.0-MHz scan range with 0.4-Hz steps with reference to the Rb clock. Experimental results demonstrate that the P-branch lines of the H13CN reference cell can be observed with a signal-to-noise ratio reaching 350 for the most intense line.
Highlights
In synchronization to each other[20], or the heterodyne beat signal has to be monitored by combining a set of continuous-wave lasers of known wavelengths[22]
As an alternative method, FT spectroscopy is performed by sweeping the repetition rate of the femtosecond laser being used as the light source
Emphasis was given to constructing a compact, robust FTS system demonstrating the effectiveness of femtosecond lasers as the light source for diverse spectroscopic applications over broad spectral bandwidths
Summary
In synchronization to each other[20], or the heterodyne beat signal has to be monitored by combining a set of continuous-wave lasers of known wavelengths[22] In this investigation, as an alternative method, FT spectroscopy is performed by sweeping the repetition rate (fr) of the femtosecond laser being used as the light source. Sampling errors may be corrected by incorporating a separate reference interferometer for elaborate tracing of the actual temporal variation of the unbalance length throughout the sampling process[23] Such a posteriori error compensation requires excessive data recording and subsequently a large amount of computation to reconstruct the undistorted interferogram; besides these problems, quantifying the uncertainty of the utilized reference interferometer with traceability to a certified frequency standard remains an essential task. Emphasis was given to constructing a compact, robust FTS system demonstrating the effectiveness of femtosecond lasers as the light source for diverse spectroscopic applications over broad spectral bandwidths
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