Watt-scale 50-MHz source of single-cycle waveform-stable pulses in the molecular fingerprint region

Abstract

We report a coherent mid-infrared (MIR) source with a combination of broad spectral coverage (6-18 μm), high repetition rate (50 MHz), and high average power (0.5 W). The waveform-stable pulses emerge via intrapulse differencefrequency generation (IPDFG) in a GaSe crystal, driven by a 30-W-average-power train of 32-fs pulses spectrally centered at 2 μm, delivered by a fiber-laser system. Electro-optic sampling (EOS) of the waveform-stable MIR waveforms reveals their single-cycle nature, confirming the excellent phase matching both of IPDFG and of EOS with 2-μm pulses in GaSe.

Multi-octave spanning, Watt-level ultrafast mid-infrared source

“…By phase matching in a suitable nonlinear medium, opposite wings of the broad input spectrum can mix and generate photons in the MIR. Recently IDFG has been shown to afford conversion efficiencies greater than 1% while maintaining more than one octave of bandwidth [41,42]. In particular, by driving with a central wavelength of 2 μm it is possible to take advantage of the higher damage threshold and broader phase matching bandwidth provided by crystals such as gallium selenide (GaSe), while exploiting a lower quantum defect [56].…”

“…EOS works through the combination of heterodyne detection and a sum-frequency generation of the MIR beam with the time delayed probe pulse, providing a direct time-domain measurement of the idler electric field [58]. Our previous work has shown that the generated MIR pulse train is waveform-stable, with a sub-100 fs duration compressible to a single cycle [42]. Through the Fourier transform of the field, the full spectrum of the MIR pulse can be measured, spanning from approximately 5 to 18 μm (see figure 7).…”

“…One particular type of DFG process known as intra-pulse DFG (IDFG) has shown promise as a relatively simple method for waveform-stable MIR generation. Such sources offer tens-of-mW level MIR output powers with a super-octave spectral coverage [28,29,[39][40][41][42].…”

“…Their use to generate a supercontinuum spanning 2.4-5.2 μm is discussed in section 4. Section 5 presents a technique for coverage of the longer wavelength regime, provided by IDFG of 2 μm driving pulses in a Gallium Selenide crystal (GaSe) [42]. The driving pulses are precompressed to 32 fs pulse duration in another silica PCF before being focused into a GaSe crystal to generate a spectrum spanning 5.2-18 μm.…”

Mid-infrared long-pass filter for high-power applications based on grating diffraction

“…In particular, laser systems delivering trains of pulses with durations of a few tens of femtoseconds, multi-10 MHz repetition rates, and several tens of watts of average power are available today, both at 1 [4,5] and 2 μm [6,7] central wavelengths. Via parametric frequency downconversion in suitable nonlinear crystals [8], these lasers have recently established a new class of MIR radiation sources [9][10][11][12][13][14], combining broad spectral coverage with brilliance values exceeding, even those of third-generation synchrotrons [11,14], as well as with excellent temporal coherence [15,16].…”