Non-resonant wavelength modulation saturation spectroscopy in acetylene-filled hollow-core photonic bandgap fibres applied to modulation-free laser diode stabilisation

Abstract

Abstract:In this paper the application of Wavelength Modulation (WM) techniques to non-resonant saturation spectroscopy in acetylene-filled Hollow-Core Photonic Bandgap Fibres (HC-PBFs) and modulation-free Laser Diode (LD) frequency stabilisation is investigated. In the first part WM techniques are applied to non-resonant pump-probe saturation of acetylene overtone rotational transitions in a HC-PBF. A high-power DFB chip-on-carrier mounted LD is used in conjunction with a tuneable External Cavity Laser (ECL) and the main saturation parameters are characterized. In the second part a novel feedback system to stabilize the DFB emission wavelength based on the WM saturation results is implemented. Modulation-free locking of the DFB laser frequency to the narrow linewidth saturation feature is achieved for both constant and variable LD temperatures.

Laser Diode Gas Spectroscopy

“…Non-linear absorption experiments are commonly based on the so-called pump-probe scheme, where an additional weak beam is used in conjunction with the high-power source in order to detect the nonlinear signal. This experimental arrangement is of particular complexity but can lead to many useful applications, such as stabilisation of the laser diode emission wavelength (Pineda Vadillo et al, 2009) by implementing an active feedback loop, as explained in section 4.3. Nonlinear absorption signals normally possess a very narrow spectral intensity profile so it is necessary to utilise laser diodes with ultranarrow emission linewidths, in order to prevent laser-induced broadening of the gas absorption lines.…”