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Asynchronous optical sampling terahertz time-domain spectroscopy using semiconductor laser-based ultra-short pulse sources is demonstrated. A pair of hybridly mode-locked edge-emitting external cavity lasers operating at a wavelength of 830 nm is used. Terahertz traces with spectral components over a range of 250 GHz are achieved.

We analyze the influence of second and third order intracavity dispersion on a passively mode-locked diode laser by introducing a spatial light modulator (SLM) into the external cavity. The dispersion is optimized for chirped pulses with highest possible spectral bandwidth that can be externally compressed to the sub picosecond range. We demonstrate that the highest spectral bandwidth is achieved for a combination of second and third order dispersion. With subsequent external compression pulses with a duration of 437 fs are generated.

A new calibration method for dual-mask liquid crystal spatial light modulators (SLMs) is presented, which can be applied while the SLM is in the setup of a pulse shaper optimised for semiconductor laser sources. An evolutionary algorithm is used to retrieve the phase retardances from the transmitted spectral intensity.

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