Laser Light Irradiation Research Articles

Сomplex Phototherapy for Compensation of Damages Induced by High-Intensity Laser Radiation in Experiment

The aim of the investigation was to develop a new technology of complex phototherapy based on consecutive biological tissue exposure to high-intensity laser radiation and low-intensity broadband red light and to evaluate its possibilities in experiment. Materials and Methods. There were studied the effects of consecutive exposure of white rat tissues to high-intensity red and infrared radiation and low-intensity broadband red light on spontaneous and metal-catalyzed oxidative modification of proteins. The study was performed on white outbred rats with a body mass of 180 to 250 g, which were divided into 5 groups. Control group 1 included animals whose inner surface of the thigh was exposed locally to laser light radiation with a wavelength of 671 nm (red laser) and the power of 50 mW. Test group 2 underwent locally red laser radiation of the inner femoral surface and three consecutive sessions of low-intensity broadband red light exposure (a wavelength of 630 nm, light spot intensity of 5 mW/cm 2 ). Control group 3 was exposed locally to 980 nm laser radiation of the inner femoral surface (infrared laser with the power of 50 mW). Test group 4 was exposed locally to infrared laser radiation of the inner femoral surface and three consecutive sessions of low-intensity broadband red light. Group 5 (intact) was not exposed to radiation. Samples of femoral tissue and blood serum were taken on day 3 in all groups of animals. Results. The content of neutral and basic aliphatic dinitrophenylhydrazons in the tissues exposed to red and infrared laser radiation was found to be increasing. in subsequent sessions of low-intensity red light phototherapy there occurred sharp decrease in the levels of protein oxidative modification products to normal values. Conclusion. The developed technology of complex phototherapy including sessions of consecutive exposure of biological tissues to laser and broadband red light provides radiation safety of procedures.

Neoadjuvant Down-Sizing of Hilar Cholangiocarcinoma with Photodynamic Therapy--Long-Term Outcome of a Phase II Pilot Study.

Hilar cholangiocarcinoma (CC) is non-resectable in the majority of patients often due to intrahepatic extension along bile duct branches/segments, and even after complete resection (R0) recurrence can be as high as 70%. Photodynamic therapy (PDT) is an established palliative local tumor ablative treatment for non-resectable hilar CC. We report the long-term outcome of curative resection (R0) performed after neoadjuvant PDT for downsizing of tumor margins in seven patients (median age 59 years) with initially non-resectable hilar CC. Photofrin® was injected intravenously 24–48 h before laser light irradiation of the tumor stenoses and the adjacent bile duct segments. Major resective surgery was done with curative intention six weeks after PDT. All seven patients had been curatively (R0) resected and there were no undue early or late complications for the neoadjuvant PDT and surgery. Six of seven patients died from tumor recurrence at a median of 3.2 years after resection, the five-year survival rate was 43%. These results are comparable with published data for patients resected R0 without pre-treatment, indicating that neoadjuvant PDT is feasible and could improve overall survival of patients considered non-curatively resectable because of initial tumor extension in bile duct branches/segments—however, this concept needs to be validated in a larger trial.

Photocontrolled release using one-photon absorption of visible or NIR light

Light is an excellent means to externally control the properties of materials and small molecules for many applications. Light's ability to initiate chemistries largely independent of a material's local environment makes it particularly useful as a bio-orthogonal and on-demand trigger in living systems. Materials responsive to UV light are widely reported in the literature; however, UV light has substantial limitations for in vitro and in vivo applications. Many biological molecules absorb these energetic wavelengths directly, not only preventing substantial tissue penetration but also causing detrimental photochemical reactions. The more innocuous nature of long-wavelength light (>400nm) and its ability at longer wavelengths (600–950nm) to effectively penetrate tissues is ideal for biological applications. Multi-photon processes (e.g. two-photon excitation and upconversion) using longer wavelength light, often in the near-infrared (NIR) range, have been proposed as a means of avoiding the negative characteristics of UV light. However, high-power focused laser light and long irradiation times are often required to initiate photorelease using these inefficient non-linear optical methods, limiting their in vivo use in mammalian tissues where NIR light is readily scattered. The development of materials that efficiently convert a single photon of long-wavelength light to chemical change is a viable solution to achieve in vivo photorelease. However, to date only a few such materials have been reported. Here we review current technologies for photo-regulated release using photoactive organic materials that directly absorb visible and NIR light.

Photoinduced decomposition of PTCDA molecules and desorption of their fragments from the films formed on the GaAs(110) surface

Photoinduced fragmentation and desorption of thin films of perylene-3,4,9,10-tetracarboxylic dianhydride (PTCDA) vacuum-deposited on the GaAs(110) surface were studied by time-of-flight (TOF) mass spectroscopy under ultrahigh vacuum conditions. The main effects under pulsed laser light irradiation (pulse duration 10 ns, photon energy 2.34 eV, laser fluence 0.5–7 mJ/cm2) were the fragmentation of the PTCDA molecule and desorption of the resulting fragments in vacuum, whereas no desorption of the intact PTCDA molecule was recorded. The fragments included the perylene core C20H8, its half C10H4, carbon dioxide and monooxide, and atomic oxygen. The desorbed fragments of different types have significantly different kinetic energies of translational motion in the gas phase because of the nonthermal mechanism of photofragmentation and photodesorption.

The protozoan, Paramecium primaurelia, as a non-sentient model to test laser light irradiation: The effects of an 808nm infrared laser diode on cellular respiration.

Photobiomodulation (PBM) has been used in clinical practice for more than 40 years. Unfortunately, conflicting literature has led to the labelling of PBM as a complementary or alternative medicine approach. However, past and ongoing clinical and research studies by reputable investigators have re-established the merits of PBM as a genuine medical therapy, and the technique has, in the last decade, seen an exponential increase in the numbers of clinical instruments available, and their applications. This resurgence has led to a clear need for appropriate experimental models to test the burgeoning laser technology being developed for medical applications. In this context, an ethical model that employs the protozoan, Paramecium primaurelia, is proposed. We studied the possibility of using the measure of oxygen consumption to test PBM by irradiation with an infrared or near-infrared laser. The results show that an 808nm infrared laser diode (1W; 64J/cm²) affects cellular respiration in P. primaurelia, inducing, in the irradiated cells, a significantly (p < 0.05) increased oxygen consumption of about 40%. Our findings indicate that Paramecium can be an excellent tool in biological assays involving infrared and near-infrared PBM, as it combines the advantages of in vivo results with the practicality of in vitro testing. This test represents a fast, inexpensive and straightforward assay, which offers an alternative to both traditional in vivo testing and more expensive mammalian cellular cultures.

Facile Fabrication of Near-Infrared-Resonant and Magnetic Resonance Imaging-Capable Nanomediators for Photothermal Therapy.

Although many techniques exist for fabricating near-infrared (NIR)-resonant and magnetic resonance imaging (MRI)-capable nanomediators for photothermal cancer therapy, preparing them in an efficient and scalable process remains a significant challenge. In this report, we exploit one-step siloxane chemistry to facilely conjugate NIR-absorbing satellites onto a well-developed polysiloxane-containing polymer-coated iron oxide nanoparticle (IONP) core to generate dual functional core-satellite nanomediators for photothermal therapy. An advantage of this nanocomposite design is the variety of potential satellites that can be simply attached to impart NIR resonance, which we demonstrate using NIR-resonant gold sulfide nanoparticles (Au2SNPs) and the NIR dye IR820 as two example satellites. The core-satellite nanomediators are fully characterized by using absorption spectra, dynamic light scattering, ζ potential measurements, and transmission electron microscopy. The enhanced photothermal effect under the irradiation of NIR laser light is identified through in vitro solutions and in vivo mice studies. The MRI capabilities as contrast agents are demonstrated in mice. Our data suggest that polysiloxane-containing polymer-coated IONPs can be used as a versatile platform to build such dual functional nanomediators for translatable, MRI-guided photothermal cancer therapy.

Laser-Induced Hydrogen Evolution Using Metal-Free Single-Walled Carbon Nanotubes

Carbon nanomaterials have been extensively studied for energy and environmental applications. Metal-free nanostructured elemental carbons and carbon-based composites have proven to be attractive alternatives to conventional metal-based catalysts for several important chemical reactions such as dehydrogenation, oxygenation and Friedel-Crafts reactions. In particular, single-walled carbon nanotubes (SWCNTs) have been of great interest to researchers because of their unique structures and physical properties. SWCNTs have been proposed as an advanced metal-catalyst support for electrochemical catalysis. However, there is no report that SWCNTs itself is used as a photocatalyst under ambient conditions due to the poor photochemical and excited properties. Catalytic hydrogen (H2) evolution systems have been extensively studied because hydrogen is a clean energy source for the future, which should reduce dependence on fossil fuels and emissions of greenhouse gases in the long term. In many cases, noble metals such as platinum and semiconductors have been used as composite photocatalysts. However, there is no report on photocatalytic metal-free H2-evolution system using pure carbon material alone as a photocatalyst. We report herein efficient H2evolution from benzene and benzene derivatives using metal free SWCNTs alone as a photocatalyst under visible laser light irradiation (532 nm) at room temperature. Laser pulse irradiation (λ = 532 nm; 500 mW; 10 Hz) of a deaerated benzene solution (2.5 mL) containing dispersed metal-free SWCNTs (0.15 mg) resulted in efficient hydrogen evolution. The amount of hydrogen evolved by laser irradiation for 2 h reached 100 mmol (2.2 mL). When benzene was replaced by deuterated benzene (C6D6), the deuterated hydrogen molecules such as D2 and HD were also evolved efficiently. The initial rate of hydrogen evolution was 21 mmol h–1 with 50 : 1 ratio for D2 and HD, respectively. The KIE (kinetic isotope effect) value was 2.4. These results indicate that the hydrogen source is benzene. The products derived from dehydrogenation of benzene were determined by the GC-MS and HPLC analyses to be biphenyl, terphenyls, and terphenylene. The stoichiometry to produce H2and biphenyl from benzene is given by eq 1. 2 C6H6 → H2 + C6H5-C6H5 (1) The dependence of the rate of H2 evolution on the laser intensity was examined using different laser power intensities at 532 nm (0 – 82 mJ pulse–1). The initial rates of H2evolution are proportional to the fourth power of laser intensity. This suggests that a bimolecular reaction of two-photon absorbed species may be involved in the photocatalytic hydrogen evolution. On the basis of above-mentioned results, the plausible photocatalytic mechanism for hydrogen evolution in benzene is shown in Scheme 1. SWCNT was excited by two photons to form doubly excited SWCNT (SWCNT**). SWCNT** can reduce benzene to produce benzene radical anion (C6H6 •–) and the one-electron oxidized SWCNT (SWCNT•+) with the rate constant of k et1. Dimerisation of C6H6 •– occurs accompanied by hydrogen evolution to produce biphenyl dianion [(C6H5)2 2–]. Such hydrogen evolution via radical coupling of C6H6 •– has previously been reported for reduction of benzene with cesium nano carbon catalyst.3 (C6H5)2 2– can reduce benzene to produce C6H6 •– and biphenyl radical anion [(C6H5)2 •–] in benzene. Back electron transfer from (C6H5)2 •– to SWCNT•+ results in formation of biphenyl [(C6H5)2], accompanied by regeneration of SWCNT. On the other hand, C6H6 •– can reduce SWCNT to produce SWCNT•– and C6H6. The charge recombination from SWCNT•– to SWCNT•+also regenerates SWCNT. The overall stoichiometry of the photocatalytic cycle in Scheme 1 agrees with eqn (1).

Fabrication of ZnInON/ZnO multi-quantum well solar cells

We report on fabrication and photovoltaic characteristics of solar cells with ZnInON/ZnO multi-quantum wells (MQWs) in the intrinsic layer of p-i-n structure by RF magnetron sputtering. We employed two kinds of p layers: one is p-GaN and the other is p-Si. Under solar simulator light, the short-circuit current (Jsc) and the open-circuit voltage (Voc) of the solar cells on p-GaN templates are 1.9μA/cm2 and 0.16V, whereas Jsc and Voc are enhanced to 2.5μA/cm2 and 0.19V under simultaneous irradiation of green laser light (532nm) and the solar simulator light. Solar cells on p-Si substrates do not show such enhancement. A possible origin of the enhancement is a large piezoelectric field generated in strained ZnInON wells coherently grown on p-GaN template.

Bioluminescence-activated deep-tissue photodynamic therapy of cancer.

Optical energy can trigger a variety of photochemical processes useful for therapies. Owing to the shallow penetration of light in tissues, however, the clinical applications of light-activated therapies have been limited. Bioluminescence resonant energy transfer (BRET) may provide a new way of inducing photochemical activation. Here, we show that efficient bioluminescence energy-induced photodynamic therapy (PDT) of macroscopic tumors and metastases in deep tissue. For monolayer cell culture in vitro incubated with Chlorin e6, BRET energy of about 1 nJ per cell generated as strong cytotoxicity as red laser light irradiation at 2.2 mW/cm2 for 180 s. Regional delivery of bioluminescence agents via draining lymphatic vessels killed tumor cells spread to the sentinel and secondary lymph nodes, reduced distant metastases in the lung and improved animal survival. Our results show the promising potential of novel bioluminescence-activated PDT.

Adiabatic photo-steering theory in topological insulators

Feasible external control of material properties is a crucial issue in condensed matter physics. A new approach to achieving this aim, named adiabatic photo-steering, is reviewed. The core principle of this scheme is that several material constants are effectively turned into externally tunable variables by irradiation of monochromatic laser light. Two-dimensional topological insulators are selected as the optimal systems that exhibit a prominent change in their properties following the application of this method. Two specific examples of photo-steered quantum phenomena, which reflect topological aspects of the electronic systems at hand, are presented. One is the integer quantum Hall effect described by the Haldane model, and the other is the quantum spin Hall effect described by the Kane–Mele model. The topological quantities associated with these phenomena are the conventional Chern number and spin Chern number, respectively. A recent interesting idea, time-reversal symmetry breaking via a temporary periodic external stimulation, is also discussed.

Femtosecond Laser Irradiation of Plasmonic Nanoparticles in Polymer Matrix: Implications for Photothermal and Photochemical Material Alteration

We analyze the opportunities provided by the plasmonic nanoparticles inserted into the bulk of a transparent medium to modify the material by laser light irradiation. This study is provoked by the advent of photo-induced nano-composites consisting of a typical polymer matrix and metal nanoparticles located in the light-irradiated domains of the initially homogeneous material. The subsequent irradiation of these domains by femtosecond laser pulses promotes a further alteration of the material properties. We separately consider two different mechanisms of material alteration. First, we analyze a photochemical reaction initiated by the two-photon absorption of light near the plasmonic nanoparticle within the matrix. We show that the spatial distribution of the products of such a reaction changes the symmetry of the material, resulting in the appearance of anisotropy in the initially isotropic material or even in the loss of the center of symmetry. Second, we analyze the efficiency of a thermally-activated chemical reaction at the surface of a plasmonic particle and the distribution of the product of such a reaction just near the metal nanoparticle irradiated by an ultrashort laser pulse.

Facile synthesis of porous copper oxide nanostructure using copper hydroxide acetate precursor

Porous copper oxide nanostructures were synthesized by thermal decomposition of copper hydroxide acetate precursor. The precursor synthesized by a facile solution phase method presents a flower-like configuration, assembled from plate-like structures. CuO with porous features were obtained via thermal decomposition of the precursor, but morphology remains unchanged after the conversion. Under laser light irradiation, copper hydroxide acetate displays a phase transition to CuO as observed by the power dependent Raman spectroscopy.

Abstract 5380: Near-infrared-resonant IONP/Au2S core/satellites hybrid nanocomposite for imaging-guided photothermal therapy

Abstract Abstract: Photothermal therapy (PTT) using near-infrared-resonant nanomaterials including multifunctional probes with both therapeutic functions and imaging capabilities has gained great attention in recent years. However, various challenges still exist including the large size of gold nanoshells, the “melting” effect of gold nanorods, lack of imaging capability, and tedious multiple steps for making imaging-capable multifunctional probes. Consequently, it is desired to develop an effective PTT mediator with the following criteria: small size, photo stability, facile synthesis, low toxicity, and imaging capability. We report the design of a core/satellites hybrid nanocomposite with a highly crystallized iron oxide nanoparticle (IONP) core (10-20 nm) and multiple gold sulfide (Au2S) nanoparticle satellites (1-2 nm) attached to the IONP polysiloxane-containing polymer coating for imaging-guided photothermal cancer therapy. In this nanostructure, the multiple satellites (Au2S) enhance PTT, while the IONP core serves as both a photothermal mediator and magnetic resonance imaging (MRI) contrast agent to localize the tumor. To make these core/satellites nanocomposites we first modify the IONP polymer coating with (3-mercaptopropyl) trimethoxysilane followed by mixing with Au2S nanoparticles, which are made by mixing sodium sulfide (Na2S) and chloroauric acid (HAuCl4) at the designed ratio. After purification using a magnet, the TEM image shows that around 8-10 Au2S nanoparticles (1-2 nm average diameter) were attached to each IONP (15 nm in diameter). This core/satellites nanocomposite has obvious absorption in the near infrared (NIR) range and the absorption peak can be adjusted by the molar ratio of Na2S to HAuCl4. The developed nanocomposite exhibits an enhanced photothermal effects without any quenching under NIR laser light. Benefitting from the anti-biofouling polysiloxane-containing polymer coating for in vivo applications, the core/satellites nanocomposites effectively accumulate to xenograft tumor tissue (SUM-159, triple-negative breast tumor cell line) through the enhanced permeability and retention effect after tail vein injection. MRI imaging is used to locate the tumors. NIR triggered PTT, which is enhanced by the core/satellites nanoparticles within the tumor site, destroys the tumor cells, while the tumor tissues in control mice do not show any change under the same laser light irradiation. Our in vitro and in vivo data reveal that NIR-resonant IONP/Au2S core/satellites nanocomposites can be used as effective MRI imaging-guided photothermal cancer therapy. Correspondence should be addressed to: Duxin Sun, PhD, or Hongwei Chen, PhD, Department of Pharmaceutical Sciences, College of Pharmacy, The University of Michigan, 428 Church Street, Ann Arbor, MI 48109, Email: duxins@umich.edu (D. Sun); or hongweic@umich.edu (H. Chen) Citation Format: Hongwei Chen, Joseph Burnett, Xiaoqing Ren, Feng Ni, Yi Wei, Hayley Paholak, Duxin Sun. Near-infrared-resonant IONP/Au2S core/satellites hybrid nanocomposite for imaging-guided photothermal therapy. [abstract]. In: Proceedings of the 105th Annual Meeting of the American Association for Cancer Research; 2014 Apr 5-9; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2014;74(19 Suppl):Abstract nr 5380. doi:10.1158/1538-7445.AM2014-5380

Fast photocatalytic degradation of methylene blue dye using a low-power diode laser

This study focused on the application of diode lasers as alternative light sources for the fast photocatalytic degradation of methylene blue. The photocatalytic decomposition of methylene blue in aqueous solution under 443nm laser light irradiation was found to be technically feasible using Ag/AgCl nanoparticles as photocatalysts. The effects of various experimental parameters, such as irradiation time, light source, catalyst loading, initial dye concentration, pH, and laser energy on decolorization and degradation were investigated. The mineralization of methylene blue was confirmed by chemical oxygen demand analysis. The results demonstrate that the laser-induced photocatalytic process can effectively degrade methylene blue under the optimum conditions (pH 9.63, 4mg/L MB concentration, and 1.4g/L Ag/AgCl nanoparticles).

Effect Of Laser And Visible Light Irradiation On Structural And Optical Properties Of Thin Films Of Amorphous Selenium And Selenium Mercury (80:20 Composition)

This study is carried out the effect of laser and solar light irradiation on the structural and optical properties of amorphous Selenium and selenium mercury (80:20 composition). Bulk samples were prepared by thermal quenching technique and thin films were papered by thermal evaporation technique on glass substrates. Thin films of a-Se and a-SeHg were irradiated by diode laser (wavelength=405nm, power=100mW) and solar light (energy ~ 0.3MeV calculated by E =hc/λ) for different durations of time. XRD analysis of a-Se and a-SeHg show increase of peak intensity and crystallite size after irradiation indicates the enhancement of crystallinity. Raman analysis of a-Se and a-SeHg also favors this improvement of crystallinity after laser and solar light irradiation. The UV analysis shows the value of optical band gap of a-Se and a-SeHg decreases after irradiation (both laser and solar light). Also it was found that the value of Urbach’s energy decreases after laser and solar light irradiation indicates that the disorder has been reduced after irradiation. The other optical parameters like extinction coefficient and absorption coefficient changes accordingly discussed in this study. It was also found that the change of structural and optical parameters is much more in case of solar light irradiation.

Hyperacusis and Other Inner Ear Disorders Are Improving after Light Irradiation with Photobiostimulation Laser

Objectives: There are several theories about pathophysiologic mechanisms involved in hyperacusis as an inner ear disease. Several authors discuss and focus hyperacusis around neurophysiological processes currently against the cochlear poor condition. This research describes effects of treatment by laser light irradiation on hyperacusis and recognizes that hyperacusis is a poor cochlear disorder instead of other auditory or neurophysiologic processes. Methods: A prospective study of a group of 58 patients who were suffering hyperacusis from several inner ear disorders (Ménière’s, tinnitus, and other disorders) was made with laser irradiation therapy based upon a photobiostimulation energy protocol. Patients were treated twice a week for 6 weeks by irradiation of a dose of low-level laser light. A laser device with double wavelength and independent light beams were used to irradiate through the ear canal with light power irradiance of 90 to 300 mw/cm2. Results: Hyperacusis significantly improved in all patients. Ninety-nine percent of observations had a large improvement of auditory capacity and 78.9% of them reached normal discomfort levels (no hyperacusis). Dynamic range of each ear was measured before and after treatment. Conclusions: Irradiation of the cochlea with a specific dose of light laser energy produces an obvious improvement in hyperacusis and other auditory disorders. This can be evaluated by comparing the audiometric dynamic range before and after the treatment period. The results confirm that hyperacusis as a disorder is more susceptible to a poor cochlear condition than other known neurophysiological processes.

Mean transverse energy and response time measurements of GaInP based photocathodes

GaInP, which has a wider band gap than GaAs, is introduced as a photocathode for energy recovery linac (ERL). The wide band gap of material is expected to reduce the heating effect in the thermal relaxation process after high energy excitation. GaInP photocathodes exhibited higher quantum efficiency than GaAs and low thermal emittance as the same as GaAs photocathodes under green laser light irradiation. A short picosecond electron pulse was also achieved with the GaInP photocathode under 532 nm pulse laser irradiation. These experimental results demonstrate that the GaInP photocathode is an important candidate for ERL.

Post-Growth Laser Annealing for High-Performance Ge Photodiodes on Si

Ge epitaxial layers on Si have been applied to near-infrared (NIR) photodiodes (PDs) in Si photonics. Post-growth annealing at high temperatures (> ~800°C) effectively reduces the density of threading dislocations generated due to the 4% lattice mismatch between Ge and Si, leading to high-performance Ge PDs with a reduced dark current [1]. However, such a high-temperature annealing would degrade pre-processed Si devices, being an obstacle to incorporate Ge into Si CMOS process, particularly into the back end of line (BEOL). In this paper, an NIR laser annealing is proposed for selective post-growth annealing of Ge layers. Si is transparent in the NIR range with the wavelength λ above ~1.0 µm, while Ge shows a strong optical absorption up to λ ~ 1.6 µm. This indicates that Ge is selectively heated by irradiating NIR light (1.0 - 1.6 µm). In fact, Ge pin PDs on Si, fabricated using Ge layers after the irradiation of NIR laser, show a significant reduction of dark current without degradation of photodetection efficiencies.In experiments, ultrahigh-vacuum chemical vapor deposition (600°C) was used for the epitaxial growth of Ge (600 nm) on p+-Si(001) wafer, followed by the growth of thin Si cap (70 nm). Then, the samples were irradiated with a scanned CW laser light (λ = 1.07 µm, 1 mm in diameter) in the air ambience. The penetration depths are ~0.8 µm for Ge and ~1 mm for Si, respectively, suggesting the selective annealing of Ge. The laser power was typically 63 W, and the duration of irradiation was typically 12 msec. The irradiation was repeated up to 10 cycles. In order to form pin structure, phosphorous ions were implanted as n-type dopants in the Si cap and the top region of Ge, followed by an activation annealing at 600°C in a furnace. Finally, Al electrodes were formed.Figure 1 shows typical current-voltage (I-V) curves obtained at room temperature under dark. The dark current was reduced by the irradiation of laser light: at the reverse bias of 1 V, the current density was 51.3±0.7 mA/cm2 for the as-grown Ge, while those for the laser-irradiated (63 W, 12 msec) Ge were reduced to be 23.7±1.4 mA/cm2 for the repetition of 3 cycles and to 20.4±1.7 mA/cm2 for the increased repetition of 10 cycles. The reduced dark current is ascribed to the reduction of dislocation density due to the annealing induced by the laser irradiation. The obtained values are comparable to that for Ge annealed at 800°C in a furnace. Further reduction of dark current would be achieved by optimizing the condition.Free-space responsivity spectra are shown in Fig. 2. All the spectra shifted towards longer wavelengths in comparison with theoretical one for unstrained Ge, reflecting the narrowing of direct gap induced by the tensile strain in Ge, which is generated due to the thermal expansion mismatch between Ge and Si [2]. For λ < 1.55 µm, the responsivity is as large as 0.15 - 0.22 A/W for the laser-annealed samples, which is comparable to the unannealed one, while for λ > 1.55 µm, the responsivity was slightly enhanced by the annealing. This probably results from the increase of tensile strain in Ge after the laser annealing, where Ge experiences higher temperatures than that in the growth (600°C).In summary, Ge pin PDs on Si, fabricated after the NIR laser annealing, showed a significant reduction of dark current without degradation of photodetection efficiencies, being a promising way to incorporate Ge into BEOL.[1] H. -C. Luan et al., Appl. Phys. Lett. 75, 2909 (1999). [2] Y. Ishikawa et al., Appl. Phys. Lett. 82, 2044 (2003).

Micro-Raman and micro-photoluminescence study of bio-conjugated core–shell CdSe/ZnS nanocrystals

The micro-Raman and micro-photoluminescence spectra of non-conjugated and conjugated with antibody against S6K2 commercial CdSe/ZnS quantum dots (QDs) were investigated under different excitation wavelengths and at different temperatures. In the photoluminescence (PL) spectra, the additional PL band shifted on 0.6–0.65eV to higher energies from the CdSe/ZnS QD exciton PL band is revealed. The relative intensity of this band is found to be several times larger in bio-conjugated QDs, than in the non-conjugated ones. The characteristics of both PL bands (the PL intensity, spectral position and half-width of the PL band) vary similarly under continuous laser light irradiation, storage of the QD samples in the atmospheric ambience as well as during the temperature change. In the Raman spectra recorded under excitation resonant with the high-energy PL band, the additional Raman peaks at about 300cm−1 and 600cm−1, which are close to the frequency of LO and 2LO phonons of bulk CdS, are found. It is proposed that alloyed QDs with chemical composition close to CdS are responsible for the additional high-energy PL band. The possible reasons for the formation of the alloyed QDs are discussed.

Proposal of Light Curtain System Using a Hemisphere Mirror with Multiple Frequency-modulated Light Sources

Light curtains are used as a method to detect intruders at a lot of places now. However, in practice, they need to adjust the light detection element accurately in order to receive the irradiating laser light. We propose a new type of Safety Light Curtain System that uses a hemisphere mirror and LEDs in this research. The hemisphere mirror can reflect light rays surrounding of 120◦ in the vertical direction and 360◦ in horizontal direction[1]. When an LED is placed at a position that is higher than the hemisphere mirror, it is possible to reflect the light with the hemisphere mirror even if the LED is arbitrarily set up. When an intruder passes between the LED and the hemisphere mirror, the light of LED is intercepted and the output voltage of the light detecting element decreases. It can be judged by the threshold output voltage whether an intruder passed between LED and the hemisphere mirror or not. Compared with recent market products, our system has the benefits of low-cost, simple configuration, low radiation, and high efficiency.