Elliminating The Transverse Instabilities of Kerr Solitons

We show analytically, numerically, and experimentally that a transversely stable one-dimensional [(1+1)D] bright Kerr soliton can exist in a 3D bulk medium. The transverse instability of the soliton is completely eliminated if it is made sufficiently incoherent along the transverse dimension. We derive a criterion for the threshold of transverse instability that links the nonlinearity to the largest transverse correlation distance for which the 1D soliton is stableComment: 14 pages, 2 figure

Optically induced photovoltaic self-defocusing-to-self-focusing transition

We show theoretically and experimentally that the photovoltaic nonlinearity that gives rise to spatial solitons can be switched from self-defocusing to self-focusing (or vice versa) by use of background illumination. This raises the possibility of bright photovoltaic solitons in LiNbO 3 . © 1998 Optical Society of America OCIS codes: 040.5350, 220.2560, 190.5530. Optical spatial solitons, in particular photorefractive (PR) solitons, 1 -9 have been investigated extensively in the past few years. PR solitons are formed when an optical beam creates a nonuniform charge distribution that gives rise to a space-charge field, E, in the crystal. By means of the Pockels effect this field creates a refractive-index change Dn~E. Here we focus on photovoltaic (PV) solitons, which are formed in unbiased PR media that exhibit a strong bulk photovoltaic effect. 5 -8 In these crystals in an open-circuit configuration, the index change is Dn Dn 0 ͑I ͞I d ͒͞ ͓1 1 ͑I ͞I d ͔͒, where I ͑x͒ is the beam intensity, I d is the natural dark irradiance, Dn 0 2͑1͞2͒n b 3 r eff E p , and E p k eff ͑͞qmt r ͒ is the maximum attainable PV field, where k eff is the effective PV constant, q is the electron charge, m is the electron mobility, and t r is the recombination time. 2 For PV solitons the sign of Dn 0 cannot be changed in a given material because it is determined by the sign of the product ͑r eff k eff ͒, which is fixed given the wavelength and the polarization of the beam. Second, adding a background beam of intensity I b for screening solitons merely increases the background density of free carriers, which is equivalent to an increase in I d by I b . 2 (In all bright screening soliton experiments I b is used to fine-tune the nonlinearity and avoid the necessity of high applied f ields. 8 In an open circuit, in which one-dimensional beams lead to J 0 everywhere in the crystal, the nonlinearity saturates to Dn 0 for I b . . Here we show theoretically and experimentally that, if the focused and the background beams are orthogonally polarized, and if the crystal is not connected to an external resistor (open circuit), then the refractiveindex change can reverse its polarity (e.g., from selfdefocusing to self-focusing). In the short circuit this polarity reversal transition does not occur. We start with the rate and continuity equations and Gauss's law in a PR medium with electrons as the sole charge carriers, plus the scalar wave equation for the optical field E opt A͑x, z͒exp͑ikz 2 ivt͒ 1 c.c. ͑k 2pn b ͞l͒. A͑x, z͒ is the slowly varying amplitude. The crystal is illuminated uniformly by a background beam of intensity I b , which is polarized normally to the soliton. In steady state the equations are where Dn 2n b 3 r iij E͞2 is the refractive-index change, z is the propagation axis, and x is the transverse coordinate. Here n is the electron density, N d i is the density of ionized donors, J is the total current density, E is the space-charge f ield in the crystal. Relevant crystal parameters are N d , the total donor density; N A , the density of negatively charged acceptors; s, the photoionization cross section; g, the recombination coefficient ͑t r 1͞gN A ͒;´s, the low-frequency dielectric constant; k B , Boltzmann's constant; T , the temperature; m; and r eff . In Eqs. 11 In Eqs. (1) -(4), J Jî and E Eî. Ohm's law yields V 2 R 11/2 21/2 Edl RSJ, where V is the potential between the crystal's electrodes separated by l, S is the surface area of the electrodes, and R is the external resistance

Combined anti-angiogenic and cytotoxic treatment of a solid tumour: in silico investigation of a xenograft animal model’s digital twin

Anti-angiogenic (AA) treatments have received significant research interest due to the key role of an-giogenesis in cancer progression. AA agents can have a strong effect on cancer regression, by blockingnew vessels and reducing the density of the existing vasculature. Moreover, in a process termed vascularnormalisation, AA drugs can improve the abnormal structure and function of the tumour vasculature,enhancing the delivery of chemotherapeutics to the tumour site. Despite their promising potential, animproved understanding of AA treatments is necessary to optimise their administration as a monotherapy orin combination with other cancer treatments. In this work we present anin silicomultiscale cancer modelwhich is used to systematically interrogate the role of individual mechanisms of action of AA drugs intumour regression. Focus is placed on the reduction of vascular density and on vascular normalisation througha parametric study, which are considered either as monotherapies or in combination with conventional/metronomic chemotherapy. The model is specified to data from a mammary carcinoma xenograft in im-munodeficient mice, to enhance the physiological relevance of model predictions. Our results suggest thatconventional chemotherapy might be more beneficial when combined with AA treatments, hindering tumourgrowth without causing excessive damage on healthy tissue. Notably, metronomic chemotherapy has shownsignificant potential in stopping tumour growth with minimal toxicity, even as a monotherapy. Our findingsunderpin the potential of ourin silicoframework for non-invasive and cost-effective evaluation of treatmentstrategies, which can enhance our understanding of combined therapeutic strategies and contribute towardsimproving cancer treatment management

Investigation of an atmospheric pressure radio frequency helium planar plasma source in humid ambient air

Atmospheric pressure radio frequency (RF) helium plasma jets operating in open air are capable of producing abundant reactive species and are widely used in biomedical applications. A planar atmospheric pressure RF plasma is studied by diagnostics and numerical modelling in this work. A novel methodology with reduced computational time and complexity is developed by converting a two-dimensional plasma fluid model into a series of one dimensional models. The numerical model reproduced the electrical characteristics and the emission spectroscopy dynamics of the discharge in good agreement with experimental measurements. Furthermore, the air influence on the kinetics of short-lived species and long-lived species is investigated numerically. It is shown that electrons are the most abundant negative species in the discharge and their density decreases with air impurities. The increasing air impurities along the discharge channel can weaken the electric field resulting in lower ionization near the outlet, and even possibly destabilizing the discharge. Reactive oxygen species are mainly present as atomic oxygen. H2O2 is produced in the gas phase through the recombination of OH radicals and destructed by collisions with He- m . It is revealed that the important for biomedical applications singlet oxygen O-2(a) is primarily generated by direct excitation of O-2 and destructed through recombination with O(S-1). The presented model can be used to study the kinetics of reactive species in atmospheric pressure RF plasma jets working in humid ambient air typical of biomedical applications

Characterization of a helium micro-plasma jet by means of ps-TALIF and a streak camera

Atmospheric pressure plasma jets (APPJ) present rich gas-phase chemistry,transient electric fields and electron densities, low gas temperatures, etc., whichmake them very promising in various novel applications such as ambient ionizationmass spectrometry [1]. Due to their operation at atmospheric pressure, collisionalquenching of generated reactive species becomes significant, and, in some cases(e.g., excited atomic hydrogen), the corresponding effective lifetimes may fall to subnstimescales [2]. In most published studies, classic optical diagnostics (such asnanosecond –ns– TALIF and ICCD cameras) are employed to understand thekinetics of reactive atoms in APPJ. However, precise measurements of theirdensities using ns-TALIF may become challenging at atmospheric and higherpressures [2]. In this case, the use of picosecond (ps) or femtosecond (fs) TALIF aswell as ultrafast detectors for atomic density and lifetime determination is a bettersolution [2,3].This work focuses on the investigation of a μs-pulsed microtube helium APPJ bymeans of ps-TALIF (laser: Ekspla®; pulse width: ~10 ps) and a streak camera(C1091005, Hamamatsu®; few ps time resolution). The achieved spatial resolutioncan be as low as 400 μm, while we were able to measure laser-excited H-atomlifetimes down to a few hundred ps (Figure 1). The obtained H-atom density andlifetime values depend on the distance from the tube exit and the APPJ parameters(voltage, helium flow rate, …). These results are supported by electrical and OESdiagnostics. This study provides useful information for APPJ kinetic models while ithelps in the optimisation of APPJ for novel applications [1].[1] S. Brandt et al., Anal. Chim. Acta 951, 16–31, 2017[2] K. Gazeli et al., Plasma 4, 145–71, 2021[3] S-J. Klose et al., Plasma Sources Sci. Technol. 29, 125018, 202