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The power conversion efficiency (PCE) of organic solar cells (OSCs) has been gradually increasing over the past years but these emerging photovoltaic devices still suffer from relatively short life...

A unique photocurrent response of a photovoltaic cell using photosynthetic protein bacteriorhodopsin (bR) is similar to that seen in the retinal ganglion cell, therefore, there are considerable interest in utilizing bR in visual sensors. A position sensitive detector (PSD) is a monolithic photosensor utilizing photodiode surface resistance. When a spot light strikes the PSD, an electric charge proportional to the light intensity is generated at the incident position. This electric charge is driven through the resistive layer and collected by two electrodes as photocurrents, while being divided in inverse proportion to the distance between the incident position and each electrode. In this study, we present 1D 10-cm-long PSD based on bR instead of organic semiconducting polymers. A bR-PSD consists of a dip-coated bR film on a high-resistivity indium-tin-oxide (ITO)-PET film, and counter ITO-PET. The position sensitive output signals of the PSD are measured in response to the intensity-modulated light of a green laser. Nonlinearity, δ=2×RMS deviation/full scale, is a measure of the distortion of the sensor output. An acceptable device has nonlinearities of less than 15%. When the position was detected at a beam diameter of φ = 5 mm, 40 mW/cm2, and the measurement interval 1 mm, the nonlinearity was 3.42%. Especially within an area of position detection error of less than 1%, the nonlinearity was 0.33%. When a beam diameter of φ = 1.5 mm and a measurement interval 500 μm, the nonlinearity showed 0.81% within the range of the light receiving centre of 2 cm. It satisfies 15%, which is the allowable range of general nonlinearity. The bR-PSD showed excellent linearity for all increments measured. Notably, the low cost (3 Euro) and simplicity of fabricating bR-PSD, and no requirement for a bias supply are two of the major advantages over conventional semiconductor material.

β-Carotene (bCar) is a natural organic semiconductor that photo-degrades within a few minutes when exposed to sunlight in ambient conditions and that can be employed as electron donor in organic solar cell (OSC) active layers. Its fast photo-degradation kinetics make bCar an ideal molecule to study strategies to improve the durability of OSCs. Mixing bCar with [6,6]-phenyl-C71-butyric acid methyl ester (PC71BM) in a 1 : 4 ratio considerably delays the bCar photo-bleaching to produce thin films that are relatively stable when exposed to sunlight for more than an hour. Furthermore, when coated with OSC top electrodes, these active layers exhibit an even stronger resistance again photo-oxidation. Despite the easily photo-oxidized nature of bCar, the resulting bCar:PC71BM OSCs maintain their photovoltaic performances for over 6 months without additional encapsulation and display high thermal stability. In fact, the binary bCar:PC71BM active layers with a large relative concentration of PC71BM exhibit a longer operational stability than reference air-stable active layers in the organic photovoltaic field, namely, poly(2,7-carbazole-alt-dithienylbenzothiadiazole):PC71BM active layers prepared with the same electron donor to PC71BM ratio (1 : 4). The superior durability of bCar OSCs compared to PCDTBT ones can be ascribed to their higher morphological stability which is associated with lower mixing energies in small molecule:fullerene systems with respect to polymer:fullerene ones. Our results thus indicate that small molecule donors combined with PC71BM into active layers have a high potential to produce OSCs that simultaneously achieve high power conversion efficiencies and durability.

β-carotene (bCar) is an abundant natural organic semiconductor that can be extracted from tomatoes or carrots at extremely low costs. Using natural bCar as electron donor combined with a C70 derivative (PC71BM) as electron acceptor in bulk heterojunction active layers, we successfully fabricated efficient inverted organic solar cells (OSCs) processed in air without encapsulation. Unlike conventional OSCs produced with synthetic materials, higher short-circuit current densities are achieved in ultrathin active layers (∼30 nm) compared to thicker ones (∼90 nm). This peculiar behavior can be ascribed to the low hole transport properties of bCar that limit the charge collection efficiency in 90 nm thick bCar:fullerene OSCs. Our results demonstrate that higher boiling point solvents induce crystalline transformation of bCar in thin active layers resulting in OSCs with fill factors around 35% and average power conversion efficiencies (PCEs) of 0.58%. These devices demonstrate stable operation under constant ill...

Optical vortex, possessing an annular intensity profile and an orbital angular momentum owing to its helical wavefront, has been widely investigated in versatile applications, including a laser scanning microscope, optical telecommunication, and optical manipulation. In particular, optical vortex can twist an irradiated material, such as metal, silicon, polymer, and even liquid resin, to form spiral-shaped structured materials on the micro/nano scale [1–3]. The spiralling direction of such structured materials is controlled by the handedness of the optical vortex, i.e. the twisting direction of a helical wavefront. In recent years, a laser-indeed bacteria-waveguide, in which the optical radiation force collects cyanobacteria into the beam to form an optical waveguide [4], has been discovered.

A compact and low-cost motion detector based on a light-sensitive protein bacteriorhodopsin is fabricated. We show that a single photocell, which is masked with a pattern, can detect the speed and direction of a moving light without complex software algorithms. When light scans the patterned sensing area, the edges of each pattern produce polarity-reversed photocurrents depending on the light bar's speed and direction. Owing to the asymmetry of the pattern, we can detect two or four directions of the moving light. We intend to exploit this unique property in gestural manipulation with a laser pointer or fingers for remote control systems.

Bacteriorhodopsin is an attractive photosensitive biomaterial. Its patterns can be obtained via an inkjet printing method. We fabricated Gabor filtering photosensors by layering inkjet patterns, and their sensing characteristics were investigated.

We report the generation of coherent deep ultraviolet light at 199 nm with a maximum average power of 32 mW by frequency quadrupling a picosecond pulse train from a Ti:sapphire laser. Two frequency-doubling stages were taking place in resonant cavities that can enhance conversion efficiency of second harmonic generations (SHGs). To reduce the extra-loss of the resonant cavity, a Brewster-input KBe2BO3F2 (KBBF) prism coupling device (PCD) was designed and employed in the second stage SHG for the first time.

We report on frequency doubling of a single frequency cw Nd:YAG laser at wavelength of 1064 nm using a periodically poled KTiOPO 4 crystal (PPKTP) placed in a single resonant ring enhanced cavity. A maximum output power of 1.23 W, corresponding to 72% of conversion efficiency with 1.7 W of fundamental power, was achieved. This is, to the best of our knowledge, the highest power obtained at this wavelength with PPKTP crystal in an external enhanced cavity. The output power is continuously stable with a peak to peak fluctuation of less than 1% over 4 h owing to optimum design of an enhanced cavity; moreover, the setup is inherently simple and robust. Therefore, it is suitable to be a light source for quantum optics experiments.

Bacteriorhodopsin (bR) is an attractive photosensitive biomaterial which can be exploited for biomimetic sensing. We have developed a novel optical-flow sensing method using a bipolar photosensor array with bR wildtype and its variant (D96N).

Summary We have experimentally studied about spatial light modulation by using the early photochemical product of bacteriorhodopsin(bR) called K intermediate at room temperature. In general, it is necessary for using K intermediate to lower the temperature of bR under 77 K. In this paper, we propose a new technique to use K intermediate at room temperature. We demonstrated experimentally spatial light modulation by using K intermediate at room temperature.

A bacteriorhodopsin film is used to measure the electric-field autocorrelation function of picosecond pulses from a mode-locked Nd:YAG laser at 532 nm wavelength. The autocorrelation is performed in geometry of light self-diffraction from polarization as well as intensity gratings at very low average illumination intensity (≈ 6 mW/cm2). By comparing the determined coherence time τC = 5.0 ps with the laser pulse duration τL = 6.6 ps, obtained by the intensity autocorrelation technique, we estimate a chirp parameter of the laser pulse bτL2 = 0.86, which points out rather small phase distortions of the pulse. Broadband absorption of the film in a visible spectral range and a low-cost technology of its preparation, together with the possibility to record polarization and intensity gratings, confirm advantages of the bacteriorhodopsin (BR) film as a novel medium for the field autocorrelation.

Bacteriorhodopsin (bR) is a promising biomaterial for several applications. Optical excitation of bR at an electrode-electrolyte interface generates differential photocurrents while an incident light is turned on and off. This unique functional response is similar to that seen in retinal neurons. The bR-based bipolar photosensor consists of the bR dip-coated thin films patterned on two ITO plates and the electrolyte solution. This bipolar photocell will function as a biomimetic photoreceptor cell. The bipolar structure, due to the photocurrent being generated in alignment with the cathodic direction, makes the excitatory and inhibitory regions possible. This scheme shows our bipolar cell can act as a basic unit of edge detection and forms the artificial visual receptive field.

We present a convenient method to generate high quality single-frequency green light at a wavelength of 540 nm. It consists of a noise suppressed external cavity diode laser at a wavelength of 1080 nm by optical filtering and resonant optical feedback, and a frequency doubling of the fundamental light with an a-cut KTP crystal. Highly efficient conversion is realized by type II non-critical phase matching. A stable single-frequency operation with a maximum power of about 20 mW is performed for more than 3 h. Both the intensity noise and line-width reach the level of a monolithic nonplanar ring laser, which is well known for its extraordinarily narrow line-width and extremely low noise among available single-frequency operating lasers.

Transmission spectra and photoinduced transmission change are observed in periodic waveguide which consist of a quartz grating substrate and a thin protein film of bacteriorhodopsin. We propose a scheme to achieve all optical switching using the photoinduced refractive index change of bacteriorhodopsin.

It is well known that the centrosymmetric molecules and centrosymmetric materials don’t exhibit, at least within the dipolar scheme, second order nonlinear optical properties useful fore a large class of practical applications, such as frequency conversion through second harmonic generation or parametric processes, light amplification, electro-optic modulation for signal transmission, generation of THz pulses, etc. Therefore a lot of effort was devoted to the design of the highly efficient molecules, with large molecular first hyperpolarizability β tensor and assembling them into a noncentrosymmetric bulk material with optimized χ(2) susceptibility. The first approach is known as molecular engineering and the second as material engineering, respectively [1].

Second and third order nonlinear optical properties of C60 based composites and multilayered structures with TPP and TPN are studied by transverse optical second and third harmonic generation, respectively. The results are compared with those obtained from pristine, photolyzed in vacuum and in oxygen atmosphere C60 thin films. Second harmonic generation is observed from structures containing C60 molecules. An enhancement of the quadratic susceptibility is observed from the multilayered structures. The third harmonic generation experiments show an enhancement of the cubic susceptibility from photolyzed C60 thin films. No increase of (chi) (3) in the multilayered structures or composites is observed. A slightly larger response is obtained with the multilayered thin films as compared to the composite material.© (1996) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

We experimentally demonstrated angular selectivity in a nondestructive readout of a photochromic protein bacteriorhodopsin (bR). bR is a photochromic material which has many unique properties. Especially, its high spatial resolutional recording ability is suitable for holographic applications. From the viewpoint of latching, it is desirable to preserve a hologram after readout. The experimental result shows a weak angular selectivity in a volume hologram on bR.

By frequency quadrupling a picosecond pulse train from a Ti: Sapphire laser with a wavelength of 798 nm and a repetition rate of 82 MHz, we generated a coherent deep ultraviolet light below 200 nm. Two frequency-doubling stages take place in resonant cavities that can increase conversion efficiency. This allows an overall efficiency of 4.3% and produces an output power of up to 60 mW. In the second stage, in which a KBe2BO3F2 (KBBF) crystal was employed as a nonlinear medium, conversion efficiency is increased by about three times compared with that of the single-pass configuration. Taking into account reflective loss, conversion efficiency is improved five times.

We report the generation of quasi-continuous-wave vacuum-ultraviolet (VUV) coherent light based on a Ti:sapphire laser with two successive frequency doubling stages. In the first stage, UV light at 399 nm with power of 1.1 W was obtained by exploiting an enhanced cavity. With a KBBF crystal as nonlinear material, quasi-continuous-wave VUV coherent light with power of about 25 mW at 199.5 nm and 4.7 mW at 193.5 nm were achieved through a single-pass SHG configuration, respectively, in the second stage.

Polarization holographic gratings transform the polarization state of an incident wavefront. We have studied the diffraction properties of polarization gratings, formed with two orthogonal linearly or circularly polarized waves. For a polarization modulation recorded in the organic material bacteriorhodopsin, the diffraction efficiency and the diffracted wave polarization strongly depend on the polarization state of the read- out wave. We have given a simple theoretical treatment using the Fraun- hofer diffraction integral. The experimental results have been interpreted in terms of this simplified model. © 2002 Society of Photo-Optical Instrumentation Engineers. (DOI: 10.1117/1.1510746)

A flexible numerical method for analyzing diffraction of real- time holograms written in bacteriorhodopsin films is described. The method calculates the propagation of writing and reading beams in bac- teriorhodopsin films using the finite-differential beam propagation method. The changes of the films in refractive index and absorption are deduced from rate equations for B-state and M-state molecules. We ap- ply this method to a real-time holographic lens and calculate the spot profile on the focal plane and the diffraction efficiencies for various pa- rameter values. We also measured diffraction efficiencies experimentally and compared the values with numerical results. © 1999 Society of Photo- Optical Instrumentation Engineers. (S0091-3286(99)01601-3)

Optical pulse delay technique is important in such fields as time-resolved spectroscopy, optical sampling and very high speed time division multiplexing of digital data. This paper reports a proposal to assemble an optical pulse delay unit with a reduced number of components by using a composite zone plate and its successful implementation with a dynamic range of 300 ps delay of 40 ps diode laser pulses.