Invited Article: Multiple-octave spanning high-energy mid-IR supercontinuum generation in bulk quadratic nonlinear crystals

Abstract

Bright and broadband coherent mid-IR radiation is important for exciting and probing molecular vibrations. Using cascaded nonlinearities in conventional quadratic nonlinear crystal like lithium niobate, self-defocusing near-IR solitons have been demonstrated that led to very broadband supercontinuum generation in the visible, near-IR and short-wavelength mid-IR. Here we conduct an experiment where a mid-IR crystal pumped in the mid-IR gives multiple-octave spanning supercontinua. The crystal is cut for noncritical interaction, so the three-wave mixing of a single mid-IR femtosecond pump source leads to highly phase-mismatched secondharmonic generation. This self-acting cascaded process leads to the formation of a self-defocusing soliton at the mid-IR pump wavelength and after the self-compression point multiple octave-spanning supercontinua are observed (covering 1.6-7.0 µm). The results were recorded in a commercially available crystal LiInS 2 pumped in the 3-4 µm range, but other mid-IR crystals can readily be used as well.

Ultrafast supercontinuum generation in bulk condensed media

“…More recent numerical and experimental results show that the long wave side of the SC radiation could be enriched by the generation of broadband dispersive waves located beyond the zero dispersion wavelength of the crystals: together with the soliton the dispersive waves contribute to the octave spanning SC, which extends from 1.0 to 4.0 μm in LN [238] and from 0.9 to 2.3 μm in β-BBO [239] crystals. More recently, this approach was extended to the nonlinear crystals that are transparent in the mid-infrared range [240]. To this end, the SC covering wavelength range from 1.6 to 7.0 μm was experimentally measured in the lithium thioindate (LiInS 2 ) crystal, using the pump pulses in the 3-4 μm range.…”

Parametrically Tunable Soliton-Induced Resonant Radiation by Three-Wave Mixing

“…The simulations used as an initial condition quantum noise seeds corresponding to the Wigner representation (on average 1/2 photon per discrete time grid, see [29] for details). Randomizing this noise seed gave us the opportunity to calculate the complex first order degree of coherence.…”

“…Recently other non-standard 4WM terms were shown to support RR waves, namely the conjugate SPM term |A| 2 A * [13-16] and third-harmonic generation term A 3 [17, 18].Phase-mismatched (cascaded) three-wave mixing (3WM) in quadratic nonlinear crystals can generate a negative self-defocusing Kerr-like nonlinearity [19,20], and when a temporal soliton is excited [21] this gives octave-spanning supercontinua [22][23][24][25] that are filament free [26][27][28][29]. So far, only RR waves generated by the cascaded self-defocusing SPM effect have been verified [27][28][29]. In this Letter we show that a new class of RR waves exist in quadratic nonlinear crystals, induced by the soliton through the 3WM processes sum-frequency generation (SFG, A 2 ) and difference-frequency generation (DFG, A * A).…”

Soliton-plasma nonlinear dynamics in mid-IR gas-filled hollow-core fibers

“…Moreover, nonlinear optics in the mid-IR is currently a very active research field for supercontinuum generation [7,8] and few-cycle pulses [9], in particular exploiting filamentation in bulk media. The pulse energy limit of ∼1 μJ of filamentationbased supercontinua [8,9] was only recently overcome by exploiting effective self-defocusing effects in bulk crystals [10]. HC gas-filled fibers instead provide an interesting alternative as they also can sustain 10s of microjoule pulse energies, tolerate mutiple-watts of average powers, provide a clean spatial mode profile, and give flexible beam delivery.…”