Generation and multi-octave shaping of mid-infrared intense single-cycle pulses


The generation of intense mid-infrared (mid-IR) optical pulses with customizable shape and spectra spanning a multipleoctave range of vibrational frequencies is an elusive technological capability. While some recent approaches to mid-IR supercontinuum generation—such as filamentation, multicolour four-wave-mixing and optical rectification1–8—have successfully generated broad spectra, no process has been identified for achieving complex pulse shaping at thegeneration step. Theadiabatic frequency converter9,10 allows for a one-to-one transfer of spectral phase through nonlinear frequency conversion over a larger-than-octave-spanning range and with an overall linear phase transfer function. Here, we show that we can convert shaped near-infrared (near-IR) pulses to shaped, energetic, multi-octave-spanning mid-IR pulses lasting only 1.2 optical cycles, and extendable to the sub-cycle regime. We expect this capability to enable a new class of precisely controlled nonlinear interactions in the mid-IR spectral range, from nonlinear vibrational spectroscopy to strong light–matter interactions and single-shot remote sensing. The mid-IR wavelength regime is of particular importance to materials science, chemistry, biology and condensed-matter physics, as it covers the fundamental vibrational absorption bands of many gaseous molecules, biomolecules and solid-state compounds. In the past decade, the advent of high-pulse-energy and ultrashort-duration mid-IR sources by nonlinear frequency conversion has ushered in a new range of nonlinear light–matter interactions. High mid-IR peak powers allow for the tracking of the energy flow dynamics (by, for example, multidimensional spectroscopy11), the coherent control of lattice displacements through nonlinear phononics12, or precise control of electron wavepacket dynamics on the timescale of vibrational motion, making it possible to observe chemical transition states13 and secondary sources of coherent soft-X-ray light14, for example. In these applications, the establishment of mid-IR sources that feature not only an extreme bandwidth, but also an arbitrary control of the pulse shape, will drive their respective fields forward. In nonlinear vibrational spectroscopy, 10-fs temporal resolution and high spectral resolution could be achieved while covering distinct vibrational resonances across multiple functional groups, but flat spectral phase and multiple pulse sequences precisely controlled in timing and relative phase (for example, for phase cycling) are necessary15. For strongfield physics, parametric amplifiers commonly provide carrierenvelope phase stability16. However, shorter and brighter X-ray pulses are predicted to be achievable via high-harmonic generation when the full complex envelope can be tailored17,18, and the coherent control of a molecular wavepacket requires a precisely timed interaction19. Further, applications such as single-shot remote sensing and biological imaging, made possible thanks to bright and wide-bandwidth sources, could become robust to changes in the dispersion of the pathway between source and target through adaptive pre-compensation20,21. To date, octave-spanning sources of mid-IR light have not allowed pre-generation pulse shaping in order to customize the resulting amplitude and phase. This is because many of the most successful technologies for octave-spanning mid-IR generation rely on self-phase modulation (for example, supercontinuum generation, filamentation, soliton compression, and so on), hence the spectral broadening is inexorably tied to the temporal phase and amplitude evolution during generation. In these devices, complex pulse shaping can only be achieved by a post-conversion pulse shaper, as shaping prior to conversion would upset the desired nonlinear pulse evolution. The same limitation is true of common threewave-mixing sources of mid-IR light such as optical parametric amplification (OPA) and difference frequency generation (DFG), in which the transfer functions for phase and amplitude are nonlinear in pulse intensity or require a temporally compressed driver pulse. Moreover, post-conversion shaping based on traditional pulse shapers such as spatial light modulators inside grating pairs and acousto-optic programmable dispersive filters (AOPDF) is a technically difficult proposition for octave-spanning bandwidths. And while extreme ultrashort pulse shaping through the modular control of distinct bands within a pulse synthesizer has become a reality in recent years22, these devices grow more complex as spectral width is extended and, in fact, have not yet covered the so-called ‘functional-group’ mid-IR range (corresponding to ∼2.5–7 μm). Our approach, outlined in Fig. 1a, employs adiabatic difference frequency generation (ADFG) to produce energetic and octavespanning shaped pulses in the mid-IR. We used adiabatic downconversion of shaped near-IR laser pulses in an aperiodically poled magnesium-oxide-doped congruent lithium niobate (MgO: CLN) crystal to produce a single-cycle pulse spanning a range between 1.8 μm and 4.4 μm at −10 dB from the peak, with a pulse duration of 11 fs (1.2 optical cycles) and a pulse energy of 1.5 μJ. Moreover, we demonstrated an unprecedented capability to shape the mid-IR pulses over their entire bandwidth, achieved by preadjusting the amplitude and phase of the near-IR pulse prior to conversion with a common sub-octave-bandwidth pulse shaper. Adiabatic sumand difference-frequency generation have been recently investigated for nonlinear wave mixing, and allow for the circumvention of the usual efficiency–bandwidth trade-off and

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@inproceedings{Krogen2017GenerationAM, title={Generation and multi-octave shaping of mid-infrared intense single-cycle pulses}, author={Peter Ra Krogen and Haim Suchowski and Houkun Liang and Noah Flemens and Kyung-Han Hong and Franz X. K{\"a}rtner and Jeffrey W . Moses}, year={2017} }