Single-Shot Microsecond-Resolved Spectroscopy Of The Bacteriorhodopsin Photocycle With Quantum Cascade Laser Frequency Combs

Time-resolved vibrational spectroscopy is an important tool for understanding biological processes and chemical reaction pathways. Today, all available methods to our knowledge require many repetitions of an experiment to acquire a microsecond time-res. mid-IR spectrum. We present the IRspectrometer, a quantum cascade laser dual frequency comb spectrometer. It allows for parallel acquisition of hundreds of mid-infrared wavelengths with microsecond time resolution. The formation of the light-activated L, M and N-states in bacteriorhodopsin - which only have µs to ms lifetimes - has been recorded with our setup: e.g. infrared response of bacteriorhodopsin to 10 ns visible light pulses with microsecond time-resolution. The different wavelengths were all measured in parallel thanks to the dual-comb approach. The spectra as well as the kinetics show good agreement with those from step-scan FTIR measurements. As a benchmark, the spectral signature of several intermediate states of the bacteriorhodopsin photocycle has been recorded in a single shot measurement. This approach greatly reduces the complexity of time-resolved bio-spectroscopy measurements in the mid-infrared which currently require many repetitions.