TR-OS (IR)

This setup for Time-Resolved Optical Spectroscopy (TR-OS) offers high flexibility. Thanks to extended-range InGaAs linear array detectors, it provides an ultra-broadband probe range, spanning the interval 500-1600 nm (corresponding to 0.8-2.5 eV) of a supercontinuum spectrum. The setup can probe either the reflectivity or the transmittivity of a sample. A second linear array detector is used as a reference channel to improve the signal-to-noise ratio. The seed laser is the Coherent RegA amplifier operating at 250 kHz repetition rate. As a pump, we use the fundamental of the laser (at 800 nm, 1.55 eV) or its second harmonics (at 400 nm, 3.1 eV). Other probe options are allowed, including single-color detection with high-speed modulation. The single-color probe is obtained either upon filtering the supercontinuum probe beam with filters or by a tunable OPA beam. The OPA output can be used also as a pump, in the range of 1200-1400 nm. Recently, we extended the setup with a double-pump option (at 800 nm).

The figure shows a map of the differential reflectivity, ΔR/R, acquired on a bulk sample of 2H-MoTe₂. The wide photon energy range probed simultaneously allows to reveal the spectral fingerprints of five excitons, indicated with the letters A & A’ (first and second exciton states resulting from e-h interaction between the topmost valence band and the conduction band at K), B & B’ (first and second exciton states resulting from e-h interaction between the lowest valence band and the conduction band at K) and C (indirect exciton KΣ). The exciton population decays on a ≈10s ps timescale, as the trend displayed demonstrates.