Dual-comb optical metrology

Dr Hollie Wright and Dr Toby Mitchell from the Ultrafast Optics Group at HWU will give a pair of talks on the theme of dual-comb optical metrology.

Hollie Wright - Two-photon dual-comb LiDAR

Time-of-flight LiDAR involves directing laser pulses at a target object and recording the time taken for the reflected pulse to return to the detector. The technique provides absolute distance measurements over long ranges but is limited in precision by the timing resolution of state-of-the-art detectors. Typical systems have electronics with sub-100ps timing resolutions, equating to few-cm precisions. We have developed a dual-comb variation in which the probe pulses are time-gated with pulses from a near identical comb, creating intensity cross-correlations. We detect these cross-correlations with two-photon absorption, yielding a strongly non-linear signal. By using these cross-correlations as the trigger for LiDAR timing electronics, we magnify the true time-of-flight by a factor of frep/(∆frep ). Thus, despite being limited to electronics with modest timing resolutions, we have achieved single-shot measurements with few-µm precisions. With averaging, we achieved sub-100nm precisions in 3s.

Toby Mitchell - Dynamic Measurements at up to 130-kHz Sampling Rates Using Ti:sapphire Dual-Comb Distance Metrology

By using band-limited detection we demonstrate Ti:sapphire dual-comb distance metrology at >100 kHz, providing few-nm precision in 100 ms with a non-ambiguity range of 29 cm. Exemplar dynamic measurements of audio waveforms are presented.