Compact mode-locked Er-doped fiber laser for broadband cavity-enhanced spectroscopy

Abstract

We report the design and characteristics of a simple and compact mode-locked Er-doped fiber laser and its application to broadband cavity-enhanced spectroscopy. The graphene mode-locked polarization maintaining oscillator consumes less than 5 W of power. It is thermally stabilized, enclosed in a 3D printed box, and equipped with three actuators that control the repetition rate: fast and slow fiber stretchers, and metal-coated fiber section. This allows wide tuning of the repetition rate and its stabilization to an external reference source. The applicability of the laser to molecular spectroscopy is demonstrated by detecting CO 2 in air using continuous-filtering Vernier spectroscopy with absorption sensitivity of 5.5 × 10 −8 cm −1 in 50 ms.

Robust, Fast and Sensitive Near-Infrared Continuous- Filtering Vernier Spectrometer

“…3(a), is caused by the etalon fringes remaining after the baseline correction procedure and by uncertainties in the frequency scale calibration. Nevertheless, the relative amplitude of the residuum is lower than what was observed in previous CF-VS demonstrations employing the rotating diffraction grating and active stabilization using either an Er-doper fiber laser [31] or a mid-infrared optical parametric oscillator [28]. The improvement is brought partly by the lack of high-speed active stabilization whose gain depended on the amplitude of the signal (and thus distorted the absorption lines), and partly by the silicon etalon used for frequency calibration, which has a better fringe contrast than the CaF 2 etalon used in the previous works.…”

“…We record spectra of CO 2 covering 1.7 THz of bandwidth at 1575 nm, and of CH 4 , covering 2.7 THz at 1650 nm. The noise equivalent absorption at 1575 nm is 5 × 10 −9 cm −1 Hz −1/2 , which is better than in previous demonstrations of the technique in the same spectral region, using a spectrometer with the galvo scanner and the same Er-doped fiber laser [31] or a commercial comb source [29], or using a Czerny-Turner spectrometer with scanned mirror and a CCD camera [36]. Moreover, the demonstrated absorption sensitivity is comparable to that of other robust cavity-enhanced techniques, e.g.…”

“…We demonstrated a new, improved design of a continuous-filtering Vernier spectrometer based on a compact fs Er-doped fiber laser and a rotating aperture that selects one Vernier order. The simplified and more robust spectrometer acquires spectra with similar resolution as in previous demonstrations of the technique (a few GHz), but at 5 times faster rates (up to 100 Hz) [28,29,31]. Some spectra were acquired at scanning speeds above the adiabatic limit, and we introduced a simple Lorentzian correction function to the theoretical model of the absorption spectrum that well reproduces the reduction of the signal at these scanning speeds.…”

“…The spectrometer is based on an entirely fiberized polarization-maintaining (PM) femtosecond Er-doped fiber laser source, described in detail in Ref. [31]. The source consists of a thermally stabilized oscillator with 125 MHz repetition rate and an amplifier.…”

A 200 MHz Compact Environmentally-Stable Mode-Locked Figure-9 Fiber Laser

“…Controlling the external environment of the laser is the former, specifically placing the laser in a thermotank or a well-controlled room. However, it must be carefully controlled to ensured that the exterior remains unchanged [10][11][12][13]. Additionally, a phase-locking system can stabilize the pulse source parameters, and excellent performance can be obtained [14][15][16].…”