GaAs-chip-based mid-infrared supercontinuum generation

The mid-infrared spectral region opens up new possibilities for applications such as molecular spectroscopy with high spatial and frequency resolution.For example,the mid-infrared light provided by synchrotron sources has helped for early diagnosis of several pathologies.However,alternative light sources at the table-top scale would enable better access to these state-of-the-art characterizations,eventually speeding up research in biology and medicine.Midinfrared supercontinuum generation in highly nonlinear waveguides pumped by compact fiber lasers represents an appealing alternative to synchrotrons.Here,we introduce orientation-patterned gallium arsenide waveguides as a new versatile platform for mid-infrared supercontinuum generation.Waveguides and fiber-based pump lasers are optimized in tandem to allow for the group velocities of the signal and the idler waves to match near the degeneracy point.This configuration exacerbates supercontinuum generation from 4 to 9μm when waveguides are pumped at 2750 nm with few-nanojoule energy pulses.The brightness of the novel mid-infrared source exceeds that of the thirdgeneration synchrotron source by a factor of 20.We also show that the nonlinear dynamics is strongly influenced by the choice of waveguide and laser parameters,thus offering an additional degree of freedom in tailoring the spectral profile of the generated light.Such an approach then opens new paths for high-brightness mid-infrared laser sources development for high-resolution spectroscopy and imaging.Furthermore,thanks to the excellent mechanical and thermal properties of the waveguide material,further power scaling seems feasible,allowing for the generation of watt-level ultra-broad frequency combs in the mid-infrared.

Acousto-optically driven lensless single-shot ultrafast optical imaging

Driven by many applications in a wide span of scientifc fields,a myriad of advanced ultrafast imaging techniques have emerged in the last decade,featuring record-high imaging speeds above a trllion-frame-per-second with long sequence depths.Although bringing remarkable insights into various ultrafast phenomena,their application out of a laboratory environment is however limited in most cases,either by the cost,complexity of the operation or by heavy data processing.We then report a versatile single-shot imaging technique combining sequentially timed lloptical mapping photography(STAMP)with acousto-optics programmable dispersive fhItering(AOPDF)and digital in-line holography(DIH).On the one hand,a high degree of simplicity is reached through the AOPDF,which enables full control over the acquisition parameters via an electrically driven phase and amplitude spectro-temporal tailoring of the imaging pulses.Here,contrary to most single-shot techniques,the frame rate,exposure time,and frame intensities can be independently adjusted in a wide range of pulse durations and chirp values without resorting to complex shaping stages,making the system remarkably agile and user-friendly.On the other hand,the use of DIH,which does not require any reference beam,allows to achieve an even higher technical simplicity by allowing its lensless operation but also for reconstructing the object on a wide depth of field,contrary to classical techniques that only provide images in a single plane.The imaging speed of the system as well as its flexibility are demonstrated by visualizing ultrashort events on both the picosecond and nanosecond timescales.The virtues and limitations as welll as the potential improvements of this on-demand ultrafast imaging method are critically discussed.