Simultaneous and Continuous Multiple Wavelength Absorption Spectroscopy on Nanoliter Volumes Based on Frequency-Division Multiplexing Fiber-Loop Cavity Ring-Down Spectroscopy

Abstract

We demonstrate a method for measuring optical loss simultaneously at multiple wavelengths with cavity ring-down spectroscopy (CRD). Phase-shift CRD spectroscopy is used to obtain the absorption of a sample from the phase lag of intensity modulated light that is entering and exiting an optical cavity. We performed dual-wavelength detection by using two different laser light sources and frequency-division multiplexing. Each wavelength is modulated at a separate frequency, and a broadband detector records the total signal. This signal is then demodulated by lock-in amplifiers at the corresponding two frequencies allowing us to obtain the phase-shift and therefore the optical loss at several wavelengths simultaneously without the use of a dispersive element. In applying this method to fiber-loop cavity ring-down spectroscopy, we achieve detection at low micromolar concentrations in a 100 nL liquid volume. Measurements at two wavelengths (405 and 810 nm) were performed simultaneously on two dyes each absorbing at mainly one of the wavelengths. The respective concentrations could be quantified independently in pure samples as well as in mixtures. No crosstalk between the two channels was observed, and a minimal detectable absorbance of 0.02 cm(-1) was achieved at 405 nm.

Gaseous Oxygen Detection Using Hollow-Core Fiber-Based Linear Cavity Ring-Down Spectroscopy

“…Choosing a linear resonator setup facilitates the in-and outcoupling of light via the cavity mirrors. By comparison, fiber ring resonators hinge on unavailable fibercouplers for HCPBF, and more sophisticated coupling schemes are required, like fiber notch filter [24] or bending of fiber [25] for light coupling in and out of the ring resonator, respectively. The reflectivity R of the cavity mirrors allows the light pulse to pass through the cavity many times leading to an increased optical path length.…”

Passively synchronized Q-switched and mode-locked dual-band Tm3+:ZBLAN fiber lasers using a common graphene saturable absorber

“…Indeed, a number of dual-band sources with CW or pulse operation based on fiber lasers9, parametric oscillators10, and semiconductors (e.g., vertical cavity surface emitting lasers11) have been demonstrated. In particular, dual-band pulsed lasers are useful in multi-color pump-probe systems for time-resolved spectroscopy and multi-wavelength cavity ring-down spectroscopy12, or to develop transmitters operating simultaneously in two optical communication windows. Q-switching and mode-locking are the two main techniques for pulse generation in fiber lasers13.…”

Evanescent-wave comb spectroscopy of liquids with strongly dispersive optical fiber cavities

“…7 Also, an effective and minimally invasive approach consists in exploiting total internal reflection in prisms and optical fibers, where the evanescent field or the confined light is exposed along an external interface and nanoliter to picoliter samples can readily be interrogated. [8][9][10][11][12] In particular, using optical fibers, it is easy to build cheap, small-size, highfinesse resonators that do not require special care in terms of alignment, cleaning, and isolation. 11,12 On the other hand, for spectroscopic analysis of liquids, the light source spectral coverage is crucial.…”

“…[8][9][10][11][12] In particular, using optical fibers, it is easy to build cheap, small-size, highfinesse resonators that do not require special care in terms of alignment, cleaning, and isolation. 11,12 On the other hand, for spectroscopic analysis of liquids, the light source spectral coverage is crucial. Broadband incoherent sources cannot be efficiently coupled to high-finesse optical cavities, while spectral reconstruction of absorption features always needs external spectrum analyzers.…”

“…31 This figure of merit is a factor of 200 above the shot-noise limit 32 for the incident optical power in each PCR ($4 lW), but it leads to an impressive sensitivity level if compared to other laser-based fiber-cavity systems. 11,33,34 This value translates into a noise-equivalent absorption coefficient of 3 Â 10 À4 cm À1 Hz À1/2 per spectral point, considering the effective evanescent-wave interaction length of our sensor (30 lm). In addition, thanks to the comb, our sensor is capable of providing information on the absorption spectrum over a wide wavelength range.…”