Dispersive waves induced by self-defocusing temporal solitons in a beta-barium-borate crystal

Abstract

We experimentally observe long-wavelength dispersive waves generation in a BBO crystal. A soliton was formed in normal GVD regime of the crystal by a self-defocusing and negative nonlinearity through phase-mismatched quatradic interaction. Strong temporal pulse compression confirmed the formation of soliton during the pulse propagation inside the crystal. Significant dispersive wave radiation was measured in the anomalous GVD regime of the BBO crystal. With the pump wavelengths from 1.24 to 1.4 µm, tunable dispersive waves are generated around 1.9 to 2.2 µm. The observed dispersive wave generation is well understood by simulations. OCIS codes:(320. Fiber-based dispersive wave (DW) induced by solitons has been intensively investigated. It plays an essential role in fiber supercontiuum generation [1,2]. New spectral components on either the short-wavelength side or the long-wavelength side of the pump wavelength are possible by this technique with proper fiber dispersion control [3][4][5][6][7][8]. The normally small core size of the fiber, however, limits the propagating pulse energy; especially when generating DW in the long-wavelength side of the pump and multiple zero-dispersion wavelengths (ZDWs) are needed. The direct use of bulk nonlinear materials is promising for high pump energy. Most bulk nonlinear materials have normal group velocity dispersion (GVD) in the near-infrared (NIR) pump wavelength; therefore, when a conventional Kerr (self-focusing and positive) nonlinearity is employed, the study of DW generation easily falls into another dilemma: filamentation likely kicks in. Which complicates the whole process, and greatly impedes its application [9][10][11].A negative (self-defocusing) nonlinearity, e.g. the one available from a phase-mismatched quadratic process, could open a new window for DW research for the mostly used NIR pump wavelengths. The flipped sign of nonlinearity means that instead of filamentations, the generation of soliton is possible in the normal GVD regime of the bulk material in the NIR; which will then be able to stimulate efficient DW emission in the anomalous GVD regime (longer wavelength) of the crystal. Furthermore, much higher pulse energy could be supported due to * moba@fotonik.dtu.dk the absence of filamentation. The excitation and utilization of NIR soliton in the normal GVD regime by the phase-mismatched quadratic process have been reported in various nonlinear crystals [12][13][14][15][16]; especially in the most frequently used BBO crystal, by which soliton compression down to few optical cycle has been realized [14]. However, despite the success of exciting selfdefocusing temporal soliton in the BBO crystal, and the numerical prediction of the existence of such a DW emission [17], the formation of DW emission in the anomalous GVD regime of this crystal has so far never been observed experimentally. It was only recently observed directly for the first time in cascaded nonlinear media [18]: The strong few-cycle near-IR self-defocusing soliton self-compression observed i...

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

“…This type of dispersive wave is quite similar to the one observed in Kerr media, since it is mediated by fourwave mixing (FWM, degenerate 28,32 or non-degenerate case 28,33 ), but with the cascaded quadratic nonlinearity we also found that there is a unique three-wave mixing (TWM) analogue. This was recently observed experimentally for the first time 34 , where we found that in BBO the SH beam had a parametrically tunable peak, i.e.…”

“…to the long-wavelength side 30,31 . This was recently experimentally verified in bulk BBO and LN 28,32 , and together with the soliton the dispersive wave(s) constitute the octavespanning supercontinuum in the self-defocusing soliton case, which for LN can extend from 1.0-4.0 µm.…”

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].…”

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

“…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).…”