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The health risks associated with low-dose radiation, which are a major concern after the Fukushima Daiichi nuclear power plant accident (the Fukushima accident), have been extensively investigated, and the cancer risks from low-dose radiation exposure (below ~ 100 mSv) are thought to be negligible. According to World Health Organization and the United Nations Scientific Committee on the Effects of Atomic Radiation reports, the level of radiation exposure from the Fukushima accident is limited, estimating no significant increased risk from the accident. Radiation-induced cell injury is mainly caused by oxidative damage to biomolecules, including DNA, lipids and proteins. Radiation stimulates metabolic activation within the mitochondria to provide energy for the DNA damage response. Mitochondrial respiratory chain complexes I and III are the most important intracellular source of reactive oxygen species (ROS) during oxidative phosphorylation in eukaryotic cells. Manganese superoxide dismutase and glutathione are key players in redox control within cells. However, perturbation of the antioxidant response leads to chronic oxidative stress in irradiated cells. Excess ROS of mitochondrial origin is reported in cancer-associated fibroblast and promotes carcinogenesis. The aim of this review paper is to discuss critical roles of mitochondria in radiation-related cancer by introducing our recent studies. In particular, elevated mitochondrial ROS in stromal fibroblasts potentiate transforming growth factor-beta (TGF-β) signaling, which triggers smooth muscle actin (α-SMA) expression to stimulate myofibroblast differentiation. Radiation-induced myofibroblasts promote tumor growth by enhancing angiogenesis. Thus, radiation affects both malignant cancer cells and neighboring stromal cells through secretion of soluble factors.

Accidental radiation exposure that is due to a nuclear accident or terrorism using radioactive materials has severe detrimental effects on human health, and it can manifest as acute radiation syndrome depending on the dose and distribution of the radiation. Therefore, the development of radiation countermeasure agents is urgently needed to protect humans against radiation injury. Besides nuclear DNA, the mitochondria are important targets of ionizing radiation (IR) because these organelles generate reactive oxygen species (ROS). Recently, we revealed that mitochondrial ROS-activated cell signaling is associated with IR-induced tumor formation. Here, we investigated the effectiveness of ascorbic acid and epicatechin (EC) in scavenging ROS as radiation countermeasure agents by using human cells and mouse. Preradiation and postradiation treatments with EC mitigate ROS-mediated mitochondrial damage, IR-induced oxidative stress responses including reduction of superoxide dismutase activity, and elevated nuclear factor erythroid 2-related factor 2 expression, and they improve human fibroblast survival. As well as in vitro, EC mitigated ROS-mediated mitochondrial damage after exposure to IR in vivo in mouse platelets. Furthermore, oral administration of EC significantly enhanced the recovery of mouse hematopoietic cells from radiation injury in vivo. In summary, EC is a potentially viable countermeasure agent that is immediately effective against accidental IR exposure by targeting mitochondria-mediated oxidative stress.-Shimura, T., Koyama, M., Aono, D., Kunugita, N. Epicatechin as a promising agent to countermeasure radiation exposure by mitigating mitochondrial damage in human fibroblasts and mouse hematopoietic cells.

In tumor tissues, activated stromal fibroblasts, termed cancer-associated fibroblasts (CAFs), exhibit similar characteristics to myofibroblasts. CAFs promote cancer cell differentiation and invasion by releasing various factors, such as growth factors, chemokines, and matrix-degrading proteases, into neighboring tumor cells. However, the roles of tumor microenvironment in case of radiation-induced carcinogenesis remain poorly understood. We recently revealed that mitochondrial oxidative stress causes tumor microenvironment formation associated with radiation-induced cancer. Repeated low-dose fractionated radiation progressively damages fibroblast mitochondria and elevates mitochondrial reactive oxygen species (ROS) levels. Excessive mitochondrial ROS activate transforming growth factor-beta (TGF-β) signaling, thereby inducing fibroblasts activation and facilitating tumor microenvironment formation. Consequently, radiation affects malignant cancer cells directly and indirectly via molecular alterations in stromal fibroblasts, such as the activation of TGF-β and angiogenic signaling. This review summarizes for the first time the roles of mitochondrial oxidative stress in microenvironment formation associated with radiation-induced cancer. This review may help us understand the risks of exposure to low-dose radiation. The cross talk between cancer cells and stromal fibroblasts contributes to the development and progression of radiation-induced cancer.

Fibroblasts are a key stromal cell in the tumor microenvironment (TME) and promote tumor growth via release of various growth factors. Stromal fibroblasts in cancer, called cancer-associated fibroblasts (CAF), are related to myofibroblasts, an activated form of fibroblast. While investigating the role of stroma fibroblasts on radiation-related carcinogenesis, it was observed following long-term fractionated radiation (FR) that the morphology of human diploid fibroblasts changed from smaller spindle shapes to larger flat shapes. These cells expressed smooth muscle actin (α-SMA) and platelet-derived growth factor receptors, markers of myofibroblasts and CAFs, respectively. Long-term FR induces progressive damage to the fibroblast nucleus and mitochondria via increases in mitochondrial reactive oxygen species (ROS) levels. Here, it is demonstrated that long-term FR-induced α-SMA–positive cells have decreased mitochondrial membrane potential and activated oxidative stress responses. Antioxidant N-acetyl cysteine suppressed radiation-induced mitochondrial damage and generation of myofibroblasts. These results indicate that mitochondrial ROS are associated with the acquisition of myofibroblasts after long-term FR. Mechanistically, mitochondrial ROS activated TGFβ signaling which in turn mediated the expression of α-SMA in radiation-induced myofibroblasts. Finally, in vivo tumor growth analysis in a human tumor xenograft model system revealed that long-term FR-induced myofibroblasts promote tumor growth by enhancing angiogenesis. Implications: Radiation affects malignant cancer cells directly and indirectly via molecular alterations in stromal fibroblasts such as activation of TGFβ and angiogenic signaling pathways. Mol Cancer Res; 16(11); 1676–86. ©2018 AACR.

Phenanthrenequinone (PQ) doped poly-(methyl methacrylate) (PMMA) have been proven to be available material for volume polarization holographic recording. In our work, we introduced benzyl methacrylate (BzMA) into the PQ/PMMA to increase the concentration of PQ (up to 1.15wt%) within the polymeric media. The enhancement of concentration of PQ brings a mean for improving performance of material. Compared with the pure PQ/PMMA, photoinduced birefringence and diffraction intensity were multiplied by introducing BzMA. This investigation can provide a significant foundation for improving polarization holographic characteristics of PQ/PMMA by modifying the chemical composition of the material.

Ataxia telangiectasia (AT) is characterized by extreme sensitivity to ionizing radiation. The gene mutated in AT, Ataxia Telangiectasia Mutated (ATM), has serine/threonine protein kinase activity and mediates the activation of multiple signal transduction pathways involved in the processing of DNA double-strand breaks. Reactive oxygen species (ROS) created as a byproduct of the mitochondria’s oxidative phosphorylation (OXPHOS) has been proposed to be the source of intracellular ROS. Mitochondria are uniquely vulnerable to ROS because they are the sites of ROS generation. ROS-induced mitochondrial mutations lead to impaired mitochondrial respiration and further increase the likelihood of ROS generation, establishing a vicious cycle of further ROS production and mitochondrial damage. AT patients and ATM-deficient mice display intrinsic mitochondrial dysfunction and exhibit constitutive elevations in ROS levels. ATM plays a critical role in maintaining cellular redox homeostasis. However, the precise mechanism of ATM-mediated mitochondrial antioxidants remains unclear. The aim of this review paper is to introduce our current research surrounding the role of ATM on maintaining cellular redox control in human fibroblasts. ATM-mediated signal transduction is important in the mitochondrial radiation response. Perturbation of mitochondrial redox control elevates ROS which are key mediators in the development of cancer by many mechanisms, including ROS-mediated genomic instability, tumor microenvironment formation, and chronic inflammation.

Mitochondria are associated with various radiation responses, including adaptive responses, mitophagy, the bystander effect, genomic instability, and apoptosis. We recently identified a unique radiation response in the mitochondria of human cells exposed to low-dose long-term fractionated radiation (FR). Such repeated radiation exposure inflicts chronic oxidative stresses on irradiated cells via the continuous release of mitochondrial reactive oxygen species (ROS) and decrease in cellular levels of the antioxidant glutathione. ROS-induced oxidative mitochondrial DNA (mtDNA) damage generates mutations upon DNA replication. Therefore, mtDNA mutation and dysfunction can be used as markers to assess the effects of low-dose radiation. In this study, we present an overview of the link between mitochondrial ROS and cell cycle perturbation associated with the genomic instability of low-dose irradiated cells. Excess mitochondrial ROS perturb AKT/cyclin D1 cell cycle signaling via oxidative inactivation of protein phosphatase 2A after low-dose long-term FR. The resulting abnormal nuclear accumulation of cyclin D1 induces genomic instability in low-dose irradiated cells.

High-performance material plays a crucial role in holographic data storage, which is a noteworthy technology with potential applications in the field of high capacity data storage. We report on a new kind of holographic storage material based on aluminum nanoparticles (Al NPs) dispersed phenanthrenequinone-doped poly(methyl methacrylate) (PQ/PMMA) photopolymer. Al NPs are efficiently synthesized in a monomer solvent using laser ablation in liquids without chemical precursors. It is shown that an increase in diffraction efficiency and recording sensitivity is achieved in both traditional holography and polarization holography by doping with Al NPs. After 4 h of ablation, the new material exhibited an improvement in the diffraction efficiency for both traditional holography and polarization holography from 2.85% to 57.15% and from 0.6% to 4.07%, respectively. We also investigated the image recording and reconstruction performance for both traditional and polarization holography and the results indicate that the proposed material has noticeable potential as a holographic storage material. Additionally, it also possesses excellent potential for holographic position multiplexing recording. We conclude that laser ablation in a liquid is a promising option for processing low-cost nano-doped holographic storage material.

In this study we monitored protein dynamics in response to cisplatin, 5-fluorouracil, and irinotecan with different concentrations and administration modes using "reverse-phase" protein arrays (RPPAs) in order to gain comprehensive insight into the protein dynamics induced by genotoxic drugs. Among 666 protein time-courses, 38% exhibited an increasing trend, 32% exhibited a steady decrease, and 30% fluctuated within 24 h after drug exposure. We analyzed almost 12,000 time-course pairs of protein levels based on the geometrical similarity by correlation distance (dCor). Twenty-two percent of the pairs showed dCor > 0.8, which indicates that each protein of the pair had similar dynamics. These trends were disrupted by a proteasome inhibitor, MG132, suggesting that the protein degradation system was activated in response to the drugs. Among the pairs with high dCor, the average dCor of pairs with apoptosis-related protein was significantly higher than those without, indicating that regulation of protein levels was induced by the drugs. These results suggest that the levels of numerous functionally distinct proteins may be regulated by common degradation machinery induced by genotoxic drugs.

We present an experimental study on the optical polarization properties of the phenanthrenequinone-doped poly(methyl methacrylate) photopolymer materials. We discuss the diffraction efficiency with different weight ratios of phenanthrenequinone that was dissolved in the materials. In addition, we observe the diffraction efficiency difference between polarization holography and traditional holography.

Ionizing radiation (IR) elevates mitochondrial oxidative phosphorylation (OXPHOS) in response to the energy requirement for DNA damage responses. Reactive oxygen species (ROS) released during mitochondrial OXPHOS may cause oxidative damage to mitochondria in irradiated cells. In this paper, we investigated the association between nuclear DNA damage and mitochondrial damage following IR in normal human lung fibroblasts. In contrast to low-doses of acute single radiation, continuous exposure of chronic radiation or long-term exposure of fractionated radiation (FR) induced persistent Rad51 and γ-H2AX foci at least 24 hours after IR in irradiated cells. Additionally, long-term FR increased mitochondrial ROS accompanied with enhanced mitochondrial membrane potential (ΔΨm) and mitochondrial complex IV (cytochrome c oxidase) activity. Mitochondrial ROS released from the respiratory chain complex I caused oxidative damage to mitochondria. Inhibition of ATM kinase or ATM loss eliminated nuclear DNA damage recognition and mitochondrial radiation responses. Consequently, nuclear DNA damage activates ATM which in turn increases ROS level and subsequently induces mitochondrial damage in irradiated cells. In conclusion, we demonstrated that ATM is essential in the mitochondrial radiation responses in irradiated cells. We further demonstrated that ATM is involved in signal transduction from nucleus to the mitochondria in response to IR.

Background and purpose Cellular radioresistance is a major impediment to effective radiotherapy. Here, we demonstrated that long-term exposure to fractionated radiation conferred acquired radioresistance to tumor cells due to AKT-mediated enhanced aerobic glycolysis. Material and methods Two human tumor cell lines with acquired radioresistance were established by long-term exposure to fractionated radiation with 0.5 Gy of X-rays. Glucose uptake was inhibited using 2-deoxy- d -glucose, a non-metabolizable glucose analog. Aerobic glycolysis was assessed by measuring lactate concentrations. Cells were then used for assays of ROS generation, survival, and cell death as assessed by annexin V staining. Results Enhanced aerobic glycolysis was shown by increased glucose transporter Glut1 expression and a high lactate production rate in acquired radioresistant cells compared with parental cells. Inhibiting the AKT pathway using the AKT inhibitor API-2 abrogated these phenomena. Moreover, we found that inhibiting glycolysis with 2-deoxy- d -glucose suppressed acquired tumor cell radioresistance. Conclusions Long-term fractionated radiation confers acquired radioresistance to tumor cells by AKT-mediated alterations in their glucose metabolic pathway. Thus, tumor cell metabolic pathway is an attractive target to eliminate radioresistant cells and improve radiotherapy efficacy.

Organic near-infrared photorefractive molecular glasses with a phenothiazine moiety are designed and synthesized through the introduction of linear, racemic/homochiral asymmetrically branched aliphatic chains into photorefractive chromophore as an auxiliary group. The compounds are characterized with 1H-NMR, IR, FAB-MS, UV-vis, TG, DSC, etc. The effect of different aliphatic chains on the absorption and thermal properties is investigated in detail. The molar absorption coefficiency at the absorption maximum wavelength showed that the homochiral asymmetrically branched aliphatic chain has a strong hypochromic effect in the dilute solution when it is introduced into photorefractive chromophore. The DSC measurement indicated that the introduction of asymmetrically branched aliphatic chain is the key issue to design organic molecular glasses whether it is racemic or homochiral. The effect of racemic/homochiral asymmetrically branched aliphatic groups on photorefractive property is investigated carefully with poly(N-vinylcarbazole) (PVK) as a photoconductor and with (2,4,7-trinitro-9-fluorenylidene) malononitrile (TNFM) as a photosensitizer. The results suggested that the racemic group is more beneficial to the improvement of photorefractive performance than the homochiral when the homochiral cannot induce rigid photorefractive chromophore to be much more ordered. 2012 Elsevier Ltd. All rights reserved.

The properties of a light-induced absorption and two-color recording were investigated in three kinds of Ru and Fe codoped LiNbO3 crystals with different Fe concentrations. A nonvolatile hologram could be recorded at a wavelength of 633 nm when blue light was simultaneously incident on the crystal. The characteristic feature of these crystals is a high persistence factor , i.e., small loss of the hologram strength at the beginning of the readout process. The sensitivity and the dynamic range increased with increasing Fe concentration, and a high sensitivity of 0.12 cm/J and a large dynamic range of 0.53 were obtained in a 0.5 mm-thick crystal. The recording model of the nonvolatile hologram is discussed from the results of light-induced absorption measurements. 2009 Elsevier B.V. All rights reserved.

We experimentally demonstrate engineerable compression of two-colored pulses in a linearly-chirped quasi-phase-matching grating. Quadratic solitons generated from fundamental input are reshaped through cascaded parametric processes of second-harmonic generation (SHG) and the back-conversion. We use type-I (e: o + o) SHG geometry in a 50-mm-long aperiodically-poled MgO:LiNbO 3 device to satisfy the group-velocity matching condition. Simultaneously compressed fundamental and SH pulses of about 55-fs duration with small pedestal are generated from the fundamental input pulses of 95-fs duration.

The biological functions of nuclear topoisomerase I (Top1) have been difficult to study because knocking out TOP1 is lethal in metazoans. To reveal the functions of human Top1, we have generated stable Top1 small interfering RNA (siRNA) cell lines from colon and breast carcinomas (HCT116-siTop1 and MCF-7-siTop1, respectively). In those clones, Top1 is reduced ∼5-fold and Top2α compensates for Top1 deficiency. A prominent feature of the siTop1 cells is genomic instability, with chromosomal aberrations and histone γ-H2AX foci associated with replication defects. siTop1 cells also show rDNA and nucleolar alterations and increased nuclear volume. Genome-wide transcription profiling revealed 55 genes with consistent changes in siTop1 cells. Among them, asparagine synthetase (ASNS) expression was reduced in siTop1 cells and in cells with transient Top1 down-regulation. Conversely, Top1 complementation increased ASNS, indicating a causal link between Top1 and ASNS expression. Correspondingly, pharmacologic profiling showed l-asparaginase hypersensitivity in the siTop1 cells. Resistance to camptothecin, indenoisoquinoline, aphidicolin, hydroxyurea, and staurosporine and hypersensitivity to etoposide and actinomycin D show that Top1, in addition to being the target of camptothecins, also regulates DNA replication, rDNA stability, and apoptosis. Overall, our studies show the pleiotropic nature of human Top1 activities. In addition to its classic DNA nicking-closing functions, Top1 plays critical nonclassic roles in genomic stability, gene-specific transcription, and response to various anticancer agents. The reported cell lines and approaches described in this article provide new tools to perform detailed functional analyses related to Top1 function. [Cancer Res 2007;67(18):8752–61]

// Tsutomu Shimura 1 , Megumi Sasatani 2 , Kenji Kamiya 2 , Hidehiko Kawai 3 , Yohei Inaba 1 , Naoki Kunugita 1 1 Department of Environmental Health, National Institute of Public Health, Saitama, Japan 2 Department of Experimental Oncology, Research Institute for Radiation Biology and Medicine (RIRBM), Hiroshima University, Hiroshima, Japan 3 Department of Molecular Radiobiology, Research Center for Radiation Genome Medicine, Research Institute for Radiation Biology and Medicine (RIRBM), Hiroshima University, Hiroshima, Japan Correspondence to: Tsutomu Shimura, e-mail: tsimura@niph.go.jp Keywords: mitochondria, ROS, cyclin D1, low-dose radiation, AKT Received: August 20, 2015 Accepted: November 21, 2015 Published: December 09, 2015 ABSTRACT Here we investigated the cellular response of normal human fibroblasts to repeated exposure to low-dose radiation. In contrast to acute single radiation, low-dose fractionated radiation (FR) with 0.01 Gy/fraction or 0.05 Gy/fraction for 31 days increased in mitochondrial mass, decreased cellular levels of the antioxidant glutathione and caused persistent accumulation of mitochondrial reactive oxygen species (ROS). Excess ROS promoted oxidative inactivation of protein phosphatase PP2A which in turn led to disruption of normal negative feed-back control of AKT/cyclin D1 signaling in cells treated with long-term FR. The resulting abnormal nuclear accumulation of cyclin D1 causes growth retardation, cellular senescence and genome instability in low-dose irradiated cells. Thus, loss of redox control and subsequently elevated levels of ROS perturb signal transduction as a result of oxidative stress. Our study highlights a specific role of mitochondrial ROS in perturbation of AKT/cyclin D1 cell cycle signaling after low-dose long-term FR. The antioxidants N-acetyl-L-cysteine, TEMPO and mitochondrial-targeted antioxidant Mito-TEMPO provided protection against the harmful cell cycle perturbations induced by low-dose long-term FR.

The xeroderma pigmentosum group C (XPC) protein complex is a key factor that detects DNA damage and initiates nucleotide excision repair (NER) in mammalian cells. Although biochemical and structural studies have elucidated the interaction of XPC with damaged DNA, the mechanism of its regulation in vivo remains to be understood in more details. Here, we show that the XPC protein undergoes modification by small ubiquitin-related modifier (SUMO) proteins and the lack of this modification compromises the repair of UV-induced DNA photolesions. In the absence of SUMOylation, XPC is normally recruited to the sites with photolesions, but then immobilized profoundly by the UV-damaged DNA-binding protein (UV-DDB) complex. Since the absence of UV-DDB alleviates the NER defect caused by impaired SUMOylation of XPC, we propose that this modification is critical for functional interactions of XPC with UV-DDB, which facilitate the efficient damage handover between the two damage recognition factors and subsequent initiation of NER.

Cell cycle arrest in response to DNA damage is important for the maintenance of genomic integrity in higher eukaryotes. We have previously reported the novel p53-dependent S-phase checkpoint operating in mouse zygotes fertilized with irradiated sperm. In the present study, we analysed the detail of the p53 function required for this S-phase checkpoint in mouse zygotes. The results indicate that ATM kinase is likely to be indispensable for the p53-dependent S-phase checkpoint since the suppression was abrogated by inhibitors such as caffeine and wortmannin. However, ATM phosphorylation site mutant proteins were still capable of suppressing DNA synthesis when microinjected into sperm-irradiated zygotes lacking the functional p53, suggesting that the target of the phosphorylation is not p53. In addition, the suppression was not affected by alpha-amanitin, and p53 protein mutated at the transcriptional activation domain was also functional in the suppression of DNA synthesis. However, p53 proteins mutated at the DNA-binding domain were devoid of the suppressing activity. Taken together, the transcription-independent function of p53 associated with the DNA-binding domain is involved in the S-phase checkpoint in collaboration with yet another unidentified target protein(s).

We studied the electric-field-induced birefringence, the photoconductivity and the photorefractive properties of photorefractive polymer composites based on N,N'-diphenyl-N,N'-bis(3-methylphenyl)-[1,1'-biphenyl]-4,4'-diamine (TPD). Photorefractive response rate is improved in TPD-based photorefractive polymer, composed of TPD, polystyrene (PS), 4-butoxy-3-propyl-1-(4'-nitrophenylazo)benzene (m3p4) and C 6 0 . We obtained the photorefractive response time of as fast as 3.2 ms (@I = 837 mW/cm 2 , E = 40 V/μm). The photoconductivity of TPD-based photorefractive polymer is found to be greater than that of the PVK-based one.

Cascaded quadratic nonlinearities in periodically poled lithium tantalate are studied with femtosecond pulses by using the spectrally resolved two-beam coupling technique. The nonlinear phase shifts show obvious dependence on the phase mismatch conditions. Relatively large intrinsic nonlinear refraction and its anisotropy are also measured.

Photorefractive response rate in a polymer composite of poly(N-vinylcarbazole)/2,4,7-trinitro-9-fluorenone, doped with 2,5-dimethyl-4-(4'-nitrophenylazo)anisole (DMNPAA) is improved by modifying the structure of DMNPAA. We found that four kinds of modified DMNPAA with alkyl substituents have fast orientational response to an external electric field and keep large anisotropy in polarizability. Among them, 4-butoxy-3-propyl-1-(4'-nitorophenylazo)benzene has the shortest reorientation time constant of 19 ms (E=54 V/µm) and photorefractive time constant of 80 ms (I=2 W/cm2, E=54 V/µm) that are 2,300 times and 63 times faster than those of the DMNPAA composite. The mechanism of the fast reorientation in new polymer composites is investigated. The fast reorientational response is achieved by the improvement of the dispersivity in the polymer composites and the decrease of the glass transition temperature.

Tritium is used as fuel for nuclear fusion reactions and has cancer risk for workers in nuclear fusion plant by its exposure during routine operation or accidents. Tritium exists as tritiated water...

Direct measurements of carrier recombination dynamics in In0.1Ga0.9N/In0.03Ga0.97N multiple quantum well (QW) structures with different well thickness (d = 5.5, 17, 34 nm) are presented. The measurements by light-induced picosecond transient grating and time-resolved photoluminescence techniques revealed three contributing carrier recombination mechanisms at high carrier injections (“efficiency droop” conditions): stimulated emission (SE), bimolecular, and Shockley-Read-Hall. The study indicates on absence of Auger recombination rate with quadratic dependence, 1/τ ∝ N2, which was not observed up to ∼5x1019 cm-3 excess carrier density (© 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

Time- and space-resolved spin wave excitation by circularly polarized pulses was investigated in a garnet ferrite. Propagation of the spin wave was con-trolled by spatially shaping of the light pulses.

We fabricate semi-insulating InGaAs/GaAs multiple quantum wells and observe the excitonic enhancement of the photorefractivity in the Franz–Keldysh geometry at wavelengths of 0.92–0.94 μm. A maximum two-wave mixing gain of 138 cm−1 and a maximum diffraction efficiency of 1.5×10−4 are obtained. The saturation intensity and the spatial resolution are also measured by four-wave mixing. The diffraction efficiency is saturated at a high external electric field. The dominant cause of this saturation is the deviation of the excitonic electroabsorption from its quadratic law.

The performance of an externally-pumped photorefractive phase conjugator is greatly improved, especially in stability and response to signal change, by the phase control of incident beams. Using piezoelectrically-driven mirrors in all incident optical paths, the backward pump is made incoherent with the other input beams and the fluctuation of mutual mean phases between forward pump and signal beams is canceled.

The photorefractive effect was observed in He-ion-implanted semi-insulating GaN film in the UV spectral region. The photorefractive grating is induced by the electroabsorption effect near the band-edge. Two beam coupling experiments were performed at a wavelength of 363.8 nm. The experimental results indicate that absorption grating mainly contributes to the beam coupling.

Efficient second-harmonic generation of 95 fs pulses were achieved by simultaneous group-velocity matching and quasi-phase matching in a 10 mm long periodically poled potassium niobate crystal. The quasi-phase-matched bandwidth was 38 nm and second-harmonic pulse duration was 158 fs with a fundamental input pulse of 95 fs without spectral and temporal distortion in the S-band of telecommunication. Utilizing the larger off-diagonal nonlinear coefficient, d31 of potassium niobate, the conversion efficiency was significantly improved from that of periodically poled MgO-doped lithium niobate. [Appl. Phys. Lett. 82, 3388 (2003)]

Time-resolved absorption bleaching and four-wave mixing techniques have been used for studies of spin relaxation and nonequilibrium carrier dynamics in resonantly excited InGaAs/GaAs multiple quantum well structures. Kinetics of absorption bleaching at 1064 nm provided spin relaxation times of 240–280 ps and carrier lifetimes of 750–1000 ps at low excitations. At higher excitations, nearly three-fold increase of spin-relaxation rate has been measured by the FWM technique, while the decrease of carrier lifetime was much less pronounced. The kinetics of nonequilibrium carrier grating with randomized spins allowed determination of the in-plane bipolar diffusion coefficient in the wells D = 11.5 cm2 s−1 and hole mobility of 230 cm2 V−1 s−1.

Efficient pulse compression was achieved by the use of cascaded quadratic nonlinearities in 10-mm-long periodically poled MgO-doped lithium niobate. An off-diagonal component of the nonlinear coefficient was utilized for group-velocity matched cascaded interactions at the fundamental wavelength of 1560 nm. Simultaneously compressed fundamental and second-harmonic pulses of ∼35 fs duration were obtained from the 110-fs-pump pulses.

We demonstrate efficient frequency doubling of 95-fs pulses with a small temporal broadening in a 10-mm-long, periodically poled, 5-mol % MgO-doped lithium niobate crystal. Simultaneous group-velocity matching and quasi phase matching were achieved by the off-diagonal nonlinear optical coefficient d32 at telecommunications range.

Antiferromagnetic resonance in orthoferrite NdFeO 3 has been investigated using terahertz time-domain spectroscopy. A resonance at 0.5 THz was detected which was assigned to the AF-mode of the antiferromagnetic spin precession.

The intrinsic problems, such as beam fanning and internal beam reflection, in measuring the photorefractive coupling constant are discussed. We propose a new technique, the varying interaction length method, to avoid them. In this method, the coupling constant is obtained by differentiating the coupling strength that is measured with changing the interaction length. We applied this method to BaTiO 3 and obtained a 10–20% larger coupling constant compared with that of the conventional method.

InGaAs/GaAs multiple quantum well (MQW) photorefractive devices that have the sensitivity around the wavelength of 1.06 μm are fabricated and some characteristics are measured. Saturation intensity is 3.6 mW / cm 2 and cut off grating pitch is 1.4 μm . These values show that this device is usable in practical applications using Nd:YAG lasers. A vibration measurement system using two-wave mixing is also demonstrated.

Spin precession was nonthermally induced by an ultrashort laser pulse in orthoferrite DyFeO3 with a pump-probe technique. Both circularly and linearly polarized pulses led to spin precessions; these phenomena are interpreted as the inverse Faraday effect and the inverse Cotton-Mouton effect, respectively. For both cases, the same mode of spin precession was excited; the precession frequencies and polarization were the same, but the phases of oscillations were different. We have shown theoretically and experimentally that the analysis of phases can distinguish between these two mechanisms. We have demonstrated experimentally that in the visible region, the inverse Faraday effect was dominant, whereas the inverse Cotton-Mouton effect became relatively prominent in the near-infrared region., 27 pages, 8 figures

Tunable and high power ultra-short pulses in mid- and far-infrared (IR) spectral region are required for pump-probe spectroscopy of molecular vibrational structures and the low-energy excitations in solid state materials. Nonlinear optical frequency down conversion has been demonstrated for mid-IR short-pulse generation [1]. Among inorganic and organic materials, an organic nonlinear optical crystal DAST (4-dimethylamino-N-methyl–4-stilbazolium tosylate), which consists of a stilbazolium cation and a tosylate anion, is quite efficient for the frequency conversion down to THz wave region because of large nonlinear optical coefficients and relatively small absorption [2, 3]. In the present paper, we report the generation of mid-IR short-pulse in spectral range of 10 ∼ 40 µm (7.5 ∼ 30 THz) using DAST crystals.

We measured the spatial coherernce of a copper vapour laser (CVL) beam with an unstable resonator by the reversal shear interferometer. By this method, we can evaluate the spatial coherence function from a single-shot measurement. The spatial coherence width was 5 mm when an unstable resonator with a magnification factor of 60 was used. Moreover we verified the result by the theoretical calculation on the basis of the passive resonator model.

The beam from a copper vapor laser with an unstable resonator was focused in a nonlinear crystal, barium borate, for second harmonic generation. Ultraviolet light of 255.3 nm was generated with an conversion efficiency of 8.9% at an average input power of 2.55 W. The characteristics of conversion were investigated.

Mid-IR femtosecond pulse generation scheme is developed based on optical parametric amplification in periodically-poled lithium niobate with 800-nm Ti:sapphire laser as the pump. We obtained 620-nm bandwidth mid-IR pulses at center wavelength of 3.5 mum. After the compensation of the second-order dispersion, the pulses are compressed down to 42 fs.

We propose and demonstrate group-velocity mismatch compensation in cascaded third-harmonic generation. Second- and third-harmonic generation efficiency of 25% and 7%, respectively, were experimentally obtained for femtosecond pulses by use of two-dimensionally periodically-poled lithium niobate.

We improved the photorefractive polymer with mixing two kinds of nonlinear chromophores. Diffraction efficiency of 16 % with 0.1 mm thick sample, and shelf lifetime of more than 2 months were obtained.

The Pb(Zn1/3Nb2/3)-PbTiO3 crystals are grown by the flux solution methods with 3 kinds of dopants, Fe, Mn, and Rh. Photorefractive properties are investigated. We also measure the extinction spectra including the scattering, electrooptic coefficients, photoconductivity, and photovoltaic effect. The two-wave-mixing gain of more than 20 cm-1 is obtained

Most of semi-insulating compound semiconductors show photorefractive effect. Its photorefractive response is quite fast compared with paraelectric and ferroelectric crystals, or organic materials. Sometimes the effect is enhanced by the band edge effect such as the electroabsorption. However, photorefractive effect has not been reported in nitride semiconductors, which are intensely studied as promising nonlinear optical materials for the blue and ultra-violet wavelength region. In this paper, we report the observation of the photorefractive two-beam coupling in semi-insulating GaN thin crystal.

We have generated femtosecond pulses of 700-nm bandwidths in a 3–4 µm spectral range by an optical parametric amplifier based on periodically-poled LiNbO3. Numerical study indicates the possibility for generating ∼25-fs pulses by pre-chirp compensation.

We modified structure of nonlinear optical chromophore by attaching alkyl groups to improve the shelf lifetime while keeping a low glass transition temperature. We obtained a sample with modified NLO, 4-(2-ethylhexyloxy)-3-propyl-1-(4'-nitoro phenylazo)benzene (m3p2,6) which has a longer shelf lifetime of more than five months. In PVK:m3p2,6:BisCzPro:TNF (50:46:3:1 wt%) composite, the photorefractive response rate was 33 ms and diffraction efficiency was 49%, at an electric field of 100 V/µm and a total writing intensity of 942 mW/cm2. These results of high-performance should be due to the following reasons: first, the chromophore m3p2,6 acts as a plasticizer and has a larger free volume thereby enhancing the orientation of chromophore, and second, the solubility of the chromophore in polymer matrix increases, inhibiting crystallization.

We perform two kinds of computer simulations on polydisperse hard‐sphere systems; a molecular‐dynamics simulation on atomic systems and a Brownian‐dynamics simulation on colloidal suspensions. By the analyses of the mean square displacement and the radial distribution function, the simulation results suggest that the long‐time behavior of colloidal suspensions is exactly the same as that of atomic systems. It is also shown that there exist three phase regions, a liquid phase region, a metastable phase region, and a crystal phase region, where the freezing and melting points in polydisperse case are shifted to the values higher than in monodisperse case.

We report the nonvolatile holographic recording in a Ru and Fe doped LiNbO/sub 3/ crystal. The recorded hologram can be fixed as a nonvolatile hologram, without a considerable decrease of the hologram strength.