Abstract
We describe the implementation of the wavelength- and frequency-modulation spectroscopy techniques using a singly-resonant optical parametric oscillator (OPO) pumped by a fiber-amplified diode laser. Frequency modulation of the diode laser was transferred to the OPO's mid-infrared idler output, avoiding the need for external modulation devices. This approach thus provides a means of implementing these important techniques with powerful, widely tunable, mid-infrared sources while retaining the simple, flexible modulation properties of diode lasers.
Highlights
Frequency modulation techniques are widely used in laser spectroscopy to achieve a high signal-to-noise ratio and, sensitive spectroscopic detection
Wavelength-modulation spectroscopy (WMS) conventionally describes the case where the modulation frequency is much less than the width of the spectral feature of interest and the modulation index is high
In contrast to external electro-optic modulators required by other laser types, current modulation of diode lasers can be achieved over broad bandwidths, extending to several gigahertz, with minimal RF power requirements and simple control of the modulation index over a wide range
Summary
Frequency modulation techniques are widely used in laser spectroscopy to achieve a high signal-to-noise ratio and, sensitive spectroscopic detection. In contrast to external electro-optic modulators required by other laser types, current modulation of diode lasers can be achieved over broad bandwidths, extending to several gigahertz, with minimal RF power requirements and simple control of the modulation index over a wide range This flexibility allows the same laser system to be reconfigured for different FM techniques [2]. Advances in nonlinear optical materials and pump lasers have made continuous-wave singly-resonant optical parametric oscillators (OPOs) attractive sources for mid-IR spectroscopy These devices can produce watt-level output powers, far exceeding those of other mid-IR sources, while having tuning ranges of hundreds of wavenumbers [7]. Use of a diode laser-based pump source allows this to be achieved while retaining simplicity of modulation and avoiding the requirement for an external modulator in the mid-IR
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