This invention relates to a laser system with controlled carrier-envelope offset (CEO), based on a laser oscillator with Cr-doped II-VI gain material emitting laser pulses of ≥ 0.75 MW peak power. The output of the laser oscillator is broadened in a nonlinear optical element, providing laser pulses with octave-spanning spectral coverage. At least part of the broadened spectrum is frequency-doubled, such that the new second-harmonic components overlap spectrally with the fundamental. Interference of second harmonic and fundamental components (f-2f interferometer) generates a beating signal that allows to determine and/or control the CEO in a feedback loop.

This invention relates to a novel spectroscopic apparatus and method for measuring the spectral response of a sample, in particular of a biological sample to pulsed mid-infrared (MIR) radiation. The apparatus irradiates a sample with probe pulses and detects the sample response to the probe light in a temporally or spectrally resolved manner. The core of the invention is the use of one or more quantum cascade lasers (QCLs) to amplify either the probe-light pulses irradiating the sample, or to amplify the probe light and response after interaction with the sample. The QCL-based amplification allows to increase the measured signal, and thus, the detection sensitivity. While QCLs have typically limited bandwidth, the invention is also suitable for spectrally broadband probe pulses by employing a combination of several QCLs with spectrally shifted amplification windows, with the possibility to shape the amplified spectrum. Temporal gating of the amplification process further allows temporal shaping of the amplified probe pulses and/or sample response.