Self-induced birefringence of white-light continuum generated by interaction of focused femtosecond laser pulses with fused silica

White-light continuum can be induced by the interaction of intense femtosecond laser pulses with condensed materials. By using two orthogonal polarizers, a self-induced birefringence of continuum is observed when focusing femtosecond laser pulses into bulk fused silica. That is, the generated white-light continuum is synchronously modulated anisotropically while propagating in fused silica. Time-resolved detection confirms that self-induced birefringence of continuum shows a growth and saturation feature with time evolution. By adjusting laser energy, the transmitted intensity of continuum modulated by self-induced birefringence also varies correspondingly. Morphology analysis with time evolution indicates that it is the focused femtosecond laser pulses that induce anisotropic microstructures in bulk fused silica, and the anisotropic structures at the same time modulate the generated continuum.

Near-infrared laser driven white light continuum generation: materials, photophysical behaviours and applications

The current understanding, applications and future perspectives on near-infrared laser driven white light continuum generation in different materials are reviewed.

White light continuum in negative hollow-core fiber filled with inert gases

As of the writing of this work, generation of white light continuum (WLC) in hollow-core photonic crystal fibers (HCPCF) filled with gases is being thoroughly researched. These structures allow the possibility of adjusting light generation properties by changing the fill gas pressure. Kagomé hollow-core PCF and silica capillaries have been used to study the nonlinear effects in gases as they facilitate exploring these weak properties. In this paper, we numerically analyze the generation of WLC in a new type of hollow-core PCF, called negative curvature hollow-core fiber (NCHCF), itself filled with different inert gases. We show that this type of fiber is a better alternative to the Kagomé and capillary fibers because it exhibits low losses and the WLC spectrum generated presents a relatively flat wavelength span from around 400[Formula: see text]nm to 2400[Formula: see text]nm under certain circumstances.

Observations of white-light flares in NOAA active region 11515: high occurrence rate and relationship with magnetic transients

Aims. There are two goals in this study. One is to investigate how frequently white-light flares (WLFs) occur in a flare-productive active region (NOAA active region 11515). The other is to investigate the relationship between WLFs and magnetic transients (MTs). Methods. We used the high-cadence (45 s) full-disk continuum filtergrams and line-of-sight magnetograms taken by the Helioseismic and Magnetic Imager (HMI) on board the Solar Dynamics Observatory (SDO) to identify WLFs and MTs, respectively. Images taken by the Atmospheric Imaging Assembly (AIA) on board SDO were also used to show the flare morphology in the upper atmosphere. Results. We found at least 20 WLFs out of a total of 70 flares above C class (28.6%) in NOAA active region 11515 during its passage across the solar disk (E45°–W45°). Each of these WLFs occurred in a small region, with a short duration of about 5 min. The enhancement of the white-light continuum intensity is usually small, with an average enhancement of 8.1%. The 20 WLFs we observed were found along an unusual configuration of the magnetic field that was characterized by a narrow ribbon of negative field. Furthermore, the WLFs were found to be accompanied by MTs, with radical changes in magnetic field strength (or even a sign reversal) observed during the flare. In contrast, there is no obvious signature of MTs in the 50 flares without white-light enhancements. Conclusions. Our results suggest that WLFs occur much more frequently than previously thought, with most WLFs being fairly weak enhancements. This may explain why WLFs are reported rarely. Our observations also suggest that MTs and WLFs are closely related and appear cospatial and cotemporal, when considering HMI data. A greater enhancement of WL emission is often accompanied by a greater change in the line-of-sight component of the unsigned magnetic field. Considering the close relationship between MTs and WLFs, many previously reported flares with MTs may be WLFs.