Broadband sensitive pump-probe setup for ultrafast optical switching of photonic nanostructures and semiconductors

TL;DR

This paper presents a highly sensitive ultrafast pump-probe spectroscopy setup capable of studying optical switching in nanostructures with broad tunability, improved precision, and applications to various semiconductors and photonic crystals.

Contribution

It introduces a novel data acquisition method that enhances measurement sensitivity and accuracy in ultrafast pump-probe spectroscopy of nanophotonic structures.

Findings

Tenfold improvement in measurement precision over previous setups.

Successful application to silicon wafers and photonic crystals.

Accurate measurement of two- and three-photon absorption coefficients.

Abstract

We describe an ultrafast time resolved pump-probe spectroscopy setup aimed at studying the switching of nanophotonic structures. Both fs pump and probe pulses can be independently tuned over broad frequency range between 3850 and 21050 cm$^{-1}$. A broad pump scan range allows a large optical penetration depth, while a broad probe scan range is crucial to study strongly photonic crystals. A new data acquisition method allows for sensitive pump-probe measurements, and corrects for fluctuations in probe intensity and pump stray light. We observe a tenfold improvement of the precision of the setup compared to laser fluctuations, allowing a measurement accuracy of better than $\Delta$R= 0.07% in a 1 s measurement time. Demonstrations of the improved technique are presented for a bulk Si wafer, a 3D Si inverse opal photonic bandgap crystal, and z-scan measurements of the two-photon absorption coefficient of Si, GaAs, and the three-photon absorption coefficient of GaP in the infrared wavelength range.