Ultraviolet supercontinuum generation driven by ionic coherence in a strong laser field

Abstract

Supercontinuum (SC) light sources hold versatile applications in many fields ranging from imaging microscopic structural dynamics to achieving frequency comb metrology. Although such broadband light sources are readily accessible in the visible and near infrared regime, the ultraviolet (UV) extension of SC spectrum is still challenging. Here, we demonstrate that the joint contribution of strong field ionization and quantum resonance leads to the unexpected UV continuum radiation spanning the 100 nm bandwidth in molecular nitrogen ions. Quantum coherences in a bunch of ionic levels are found to be created by dynamic Stark-assisted multiphoton resonances following tunneling ionization. We show that the dynamical evolution of the coherence-enhanced polarization wave gives rise to laser-assisted continuum emission inside the laser field and free-induction decay after the laser field, which jointly contribute to the SC generation together with fifth harmonics. As proof of principle, we also show the application of the SC radiation in the absorption spectroscopy. This work offers an alternative scheme for constructing exotic SC sources, and opens up the territory of ionic quantum optics in the strong-field regime.

Improved calculation of the Mie solution and the geometrical optics approximation for large droplets

“…As can be shown (using the geometry from figure 3 in the volumetric case), these dark regions occupy about 20% of the droplet. Now we see that it is possible to cause illumination of the them if the droplet is irradiated, e.g., with an ultraviolet supercontinuum [81], containing, among others, packets with wavelengths corresponding to resonant states. Thus, supercontinuum can help overcome the problem of requiring fine tuning of parameters to create resonance [80].…”

Raman time-delay in attosecond transient absorption of strong-field created krypton vacancy

“…To uncover the involved dynamics, the physics behind the time-delay of the two resonant transitions are investigated by adopting density matrix approach 31 (see Methods and SM note 5 ) with the relevant states included: where ρ + denotes the density matrix of the ion, and the second (third) term on the right represents the injection (decay) of ion. This model has been successfully applied to the study of coherent emission from nitrogen ion 32 , here it is further developed to account for transient absorption. The following processes are considered as illustrated in Fig.…”

Ultrafast All-Optical Modulation and Efficient Third-Harmonic Generation in Two-Dimensional Perovskite Heterostructures

“…13 Along with the ultrafast optical modulation, the all-optical wavelength or frequency conversion is also the key functionality of future optical networks, which can convert the low-frequency light signal to a high-frequency light signal. 14 The nonlinear optical (NLO) processes, like the second-harmonic generation (SHG) and third-harmonic generation (THG), 15,16 have been widely explored to covert near-infrared (NIR) and mid-infrared (MIR) light into UV and visible light, which is crucial for nonlinear spectroscopy, 17 photodetection, 18 optical frequency converters, 19 UV light generation, 20 biomedical imaging, 21 etc. However, ultrafast and efficient light−matter interactions are challenging for the available optoelectronic materials.…”