Laser-induced non-linear light scattering in a suspension of black-body particles

Characteristics of non-linear scattering of powerful pulses of Q-switched YAG:Nd³⁺ laser in an aqueous suspension of submicron-sized black-body particles has been investigated. Proposed is a model describing the results of experiments. This model involves laser-induced overheating of suspended particles and vaporization of surrounding water with subsequent rapid growth of vapor shells around the particles

Effect of non-linear absorption on characteristics of laser-induced luminescence

This paper deals with the methodology of laser-induced luminescence at high excitation levels. For a case when a photodetector collects integral (over the volume) luminescence power, a method is proposed for processing the experimentally-measured luminescence power and optical transmittance as some functions of the incident laser power. The method is based on the analysis of relative increments of luminescence and transmitted laser power. Considered are two examples of mechanisms of non-linear laser-induced luminescence, namely: saturated molecular luminescence and luminescence excited via two-photon absorption

Characteristics of optical limiting in media with nonlinear absorption and scattering

A comparative study is performed for characteristics of optical limiting in the media with nonlinear absorption and scattering with the use of nanosecond-scale laser pulses. Two methods are proposed to analyze of experimental nonlinear transmittance curves. The experiments revealed differences in the shape of nonlinear transmittance curves in the media with different physical mechanisms of optical limiting. For optical limiting in suspensions of light-absorbing particles, it is concluded that the fifth-order nonlinear susceptibilities should be taken into account

Laser-induced incandescence in aqueous carbon black suspensions: the role of particle vaporization

Non-linear properties and the kinetics of laser-induced incandescence in aqueous carbon black suspensions are investigated. For explanation of the observed properties, a model, which takes into account a decrease of the size of particles caused by their vaporization under laser irradiation, is proposed

Laser-induced incandescence of silicon surface under 1064-nm excitation

Laser-induced incandescence (LII) of silicon surface is investigated under the excitation by a Q-switched YAG:Nd laser. With the increase of laser irradiation dose, the increase of LII signal is observed, which is attended by visible changes of the surface geometry. The anomalous behavior of the parameter of non-linearity of LII is observed with the increase of laser excitation power

Luminescent properties of fine-dispersed ZnS:Cu prepared using self-propagating high-temperature synthesis

Fine-dispersed ZnS doped with Cu was prepared using self-propagating hightemperature synthesis. In the photoluminescence excitation spectra, the blue shift of the host lattice excitation peak is observed for powder ZnS:Cu that contains nano- and mesosized (submicron) particles. The obtained spectra indicate that radiative recombination in meso-sized particles is significantly reduced as compared to micro-sized particles, which can be caused by the increase of non-radiative relaxation processes in surface states

Optical transmittance of carbon suspensions in polymer matrixes under powerful pulsed laser irradiation

The effect of optical limiting is investigated in the suspensions of carbon microparticles in aqueous gelatin gel and epoxy resin. Both transient and permanent changes of optical transmittance are observed after the irradiation by a Q-switched YAG:Nd³⁺ laser pulses. The experimental results are explained with taking into account the formation of micro-bubbles filled with water steam and with gaseous products of decomposition of the matrix. In the epoxy resin suspensions, the laser-induced permanent changes of transmittance are caused by pyrolysis of epoxy oligomers in the vicinity of laser-heated carbon particles

HSF2BP negatively regulates homologous recombination in DNA interstrand crosslink repair

The tumor suppressor BRCA2 is essential for homologous recombination (HR), replication fork stability and DNA interstrand crosslink (ICL) repair in vertebrates. We show that ectopic production of HSF2BP, a BRCA2-interacting protein required for meiotic HR during mouse spermatogenesis, in non-germline human cells acutely sensitize them to ICL-inducing agents (mitomycin C and cisplatin) and PARP inhibitors, resulting in a phenotype characteristic of cells from Fanconi anemia (FA) patients. We biochemically recapitulate the suppression of ICL repair and establish that excess HSF2BP compromises HR by triggering the removal of BRCA2 from the ICL site and thereby preventing the loading of RAD51. This establishes ectopic expression of a wild-type meiotic protein in the absence of any other protein-coding mutations as a new mechanism that can lead to an FA-like cellular phenotype. Naturally occurring elevated production of HSF2BP in tumors may be a source of cancer-promoting genomic instability and also a targetable vulnerability

Caffeine suppresses homologous recombination through interference with RAD51-mediated joint molecule formation

Caffeine is a widely used inhibitor of the protein kinases that play a central role in the DNA damage response. We used chemical inhibitors and genetically deficient mouse embryonic stem cell lines to study the role of DNA damage response in stable integration of the transfected DNA and found that caffeine rapidly, efficiently and reversibly inhibited homologous integration of the transfected DNA as measured by several homologous recombination-mediated gene-targeting assays. Biochemical and structural biology experiments revealed that caffeine interfered with a pivotal step in homologous recombination, homologous joint molecule formation, through increasing interactions of the RAD51 nucleoprotein filament with non-homologous DNA. Our results suggest that recombination pathways dependent on extensive homology search are caffeine-sensitive and stress the importance of considering direct checkpoint-independent mechanisms in the interpretation of the effects of caffeine on DNA repair

HSF2BP Interacts with a Conserved Domain of BRCA2 and Is Required for Mouse Spermatogenesis

The tumor suppressor BRCA2 is essential for homologous recombination (HR), replication fork stability, and DNA interstrand crosslink repair in vertebrates. We identify HSF2BP, a protein previously described as testis specific and not characterized functionally, as an interactor of BRCA2 in mouse embryonic stem cells, where the 2 proteins form a constitutive complex. HSF2BP is transcribed in all cultured human cancer cell lines tested and elevated in some tumor samples. Inactivation of the mouse Hsf2bp gene results in male infertility due to a severe HR defect during spermatogenesis. The BRCA2-HSF2BP interaction is highly evolutionarily conserved and maps to armadillo repeats in HSF2BP and a 68-amino acid region between the BRC repeats and the DNA binding domain of human BRCA2 (Gly2270-Thr2337) encoded by exons 12 and 13. This region of BRCA2 does not harbor known cancer-associated missense mutations and may be involved in the reproductive rather than the tumor-suppressing function of BRCA2. BRCA2 is a key homologous recombination mediator in vertebrates. Brandsma et al. show that it directly interacts with a testis-expressed protein, HSF2BP, and that male mice deficient for HSF2BP are infertile due to a meiotic recombination defect. They also find that HSF2BP contributes to DNA repair in mouse embryonic stem cells