High brilliance coherent light sources are sought for a diverse range of investigations and applications, e.g., ultrasensitive spectroscopy, standoff detection, chemical diagnostics, material science, ultrafast imaging and attosecond science. Here, we present such a carrier-envelope-phase stable light source, seeded by a mid-IR frequency comb, with simultaneous spectral coverage across 7 optical octaves, from the UV (340 nm) into the THz (40,000 nm). The brightness of this source exceeds the brightness of synchrotrons across the entire 7 octave spectrum and by up to 5 orders of magnitude.
We demonstrate the development of broadband, infrared frequency combs tunable from 3 to 27 microns. The source is based on using a robust, few-cycle Er:fiber comb (10 fs pulse duration) to drive intra-pulse difference frequency generation within a quasi-phase-matched nonlinear medium (e.g. periodically poled lithium niobite or orientation patterned gallium phosphide). Since the down-converted light has a longer optical period, the electric field of this longer wave light can be directly sampled by the few-cycle Er:fiber pulse via electro-optic sampling (EOS), directly yielding spectroscopic information on the infrared light. Further, by implementing EOS in a dual frequency comb configuration, we can increase the spectroscopic acquisition speed to a rate of 50 Hz. This dual-comb EOS configuration enables a measurement bandwidth spanning 370 – 3300 cm^-1 with a resolution down to the 100 MHz (0.003 cm^-1) spacing of the infrared comb. Due to the brightness of this comb source and the broad acquisition bandwidth, we can perform high resolution and high sensitivity spectroscopy on chemically and biologically relevant compounds spanning the molecular fingerprint region, with an outlook towards fast acquisition, infrared frequency comb microscopy.
Nanoscale amplification of non-linear processes in solid-state devices opens novel applications in nano-electronics, nano-medicine or high energy conversion for example. Coupling few nano-joules laser energy at a nanometer scale for strong field physics is demonstrated. We report enhancement of high harmonic generation in nano-structured semiconductors using nanoscale amplification of a mid-infrared laser in the sample rather than using large laser amplifier systems. Field amplification is achieved through light confinement in nano-structured semiconductor 3D waveguides. The high harmonic nano-converter consists of an array of zinc-oxide nanocones. They exhibit a large amplification volume, 6 orders of magnitude larger than previously reported [1] and avoid melting observed in metallic plasmonic structures. The amplification of high harmonics is observed by coupling only 5-10 nano-joules of a 3.2 µm high repetition-rate OPCPA laser at the entrance of each nanocone. Harmonic amplification (factor 30) depends on the laser energy input, wavelength and nanocone geometry [2].
[1] Vampa et al., Nat. Phys. 13, 659–662 (2017).
[2] Franz et al., arXiv:1709.09153 [physics.optics] (2017)
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