A compact, self-compression-based sub-3 optical cycle source in the $3\mbox{--}4\,\mu {\rm{m}}$ spectral range

Abstract

We report on the experimental realization of a compact, Ti:sapphire laser-pumped mid-infrared light source, which delivers sub-3 optical cycle pulses in the spectral range. The light source employs difference frequency generation in potassium titanyl arsenate crystal by mixing the signal and idler waves from a commercial near-infrared optical parametric amplifier and subsequent optical parametric amplification in LiIO3 crystal. The amplified sub-100 fs mid-infrared pulses are self-compressed down to sub-3 optical cycles by nonlinear propagation in few mm thick YAG, CaF2 and BaF2 crystals featuring anomalous group velocity dispersion in that spectral range. The self-compression is performed without the onset of self-focusing effects, hence maintaining a homogenous beam profile with energy throughput efficiency of above 90%, yielding the self-compressed pulses with sub- energy. Even larger self-compression factors (down to sub-2 optical cycles) were achieved in the filamentation regime, simultaneously producing an ultrabroadband supercontinuum, extending from the visible to the mid-infrared.

Ultrafast supercontinuum generation in bulk condensed media

“…More recent spectral measurements with 3.5 µm pulses (Fig. 14), as performed over higher dynamic range, revealed that the spectral discontinuity still exists in CaF 2 , however, demonstrating more homogenous SC spectrum in BaF 2 , which provided the spectral coverage from the visible to beyond 5 µm in the mid-infrared 200 .…”

“…In that way, sub-3 optical cycle self-compressed pulses with >10 μJ energy were obtained at 3 μm by placing the 3 mm thick YAG plate at the output of the high repetition rate OPCPA system [285,286]. The self-compression of parametrically amplified difference frequency pulses in few-mm thick YAG, CaF 2 and BaF 2 crystals down to sub-3 optical cycle widths was demonstrated in the 3-4 μm spectral range [200]. Figure 22 presents the experimental results illustrating a three-fold self-compression of 70 fs pulses with the carrier wavelength of 3 μm down to 23 fs (2.3 optical cycles) in a 3 mm-thick YAG plate, due to the interplay between the self-phase modulation and anomalous GVD and without the onset of self-focusing effects.…”

Advanced metrology for few-cycle mid-IR pulses

“…Moving the YAG close to the focus caused spectral instability. In addition, visible filamentation in the material and self-focusing of the beam was be observed, together with significant optical losses from nonlinear processes (similarly to those described for a CaF2 plate in reference [138]). Increasing the intensity even further caused optical damage on the second surface of the YAG crystal due to critical self-focusing.…”

“…The limitation is the gain bandwidth of the OPA process, which narrows the bandwidth of the amplified pulses, thus limiting the achievable shortest pulses. To generate shorter pulses, postcompression must be used, which consists of spectral broadening in a medium through the SPM process [90][91][92][93][94][95][96][97][98][99][100][101] followed by dispersion control. In the past decades, several technologies have emerged for the post-compression of laser pulses.…”

“…A less expensive and much simpler post-compression scheme for intense mid-IR pulses can be achieved by nonlinear broadening in solid-state media [98][99][100][101]. Here the nonlinear refractive index (n2) is by orders of magnitude higher compared to that of the inert gases inside a hollow-core waveguide.…”