Fast mode-hop-free acousto-optically tuned laser: theoretical and experimental investigations

Abstract

We developed a theory that describes fast mode-hop-free tuning of an external cavity diode laser in Littrow configuration with two acousto-optic modulators (AOMs) inside the laser cavity. The theory is based on synchronous shifting of the external cavity modes and the Littrow grating selectivity. It allows calculating the driving signals of both AOMs in order to reach a desired temporal variation of the laser frequency, including particularly fast tuning as well as an arbitrary shape of the tuning function. Furthermore, we present a laser setup for which the needed signals for both AOMs are generated by two direct digital synthesizer circuits. Thereby we were able to verify the theoretical predictions experimentally, achieving, e.g., sinusoidal single-mode tuning of the laser frequency over 40 GHz at a repetition rate of 10 kHz and over 12 GHz at 25 kHz. Finally, the limitations of the theory are discussed.

On the plasma chemistry of a cold atmospheric argon plasma jet with shielding gas device

“…The basic scheme of the laser system is similar to an external cavity diode laser in Littrow configuration. However, the frequency tuning is not realized by turning the grating but by altering the acoustic signal applied to the two included acousto-optic modulators (AOMs) [44,45]. In consequence, fast single mode frequency tuning with a repetition frequency of 10 kHz at a tuning range of 30 GHz is achieved due to the lack of mechanically actuated elements.…”

Spatially resolved LAAS/OES diagnostics of a free-burning Ar arc: measurements of excited atom densities

“…Laser absorption spectroscopy (LAAS) was performed by using the spectroscopic measurement system 'EasyLAAS' (neoplas control GmbH, Germany). Its main component is a novel diode laser called 'AOM laser' [30][31][32] for a 748-796 nm wavelength range. Compared to conventional diode laser systems that are mechanically tuned (e.g.…”

Review on VUV to MIR absorption spectroscopy of atmospheric pressure plasma jets

“…As most diode laser mode hop free tuning range is smaller than the absorption of a broadened line at atmospheric pressure, most scans are taken with the line maximum not in the centre of the tuning range. A different approach has been proposed by Bösel et al [115][116][117]. Using intracavity acousto-optic modulators, the wavelength of a Littrow type diode laser system is tuned mode-hop-free.…”