Fiber-based two-wavelength heterodyne displacement interferometer

High concentrating photovoltaic (HCPV) technology plays a more and more important role in solar power generation due to its extremely high efficiency. However, the efficiency of the HCPV module can be reduced by many factors. Especially, there are not enough researches and knowledge on the light intensity distribution and non-uniform illumination of different wavelengths of light concentrated by Fresnel lens. It is generally considered that the maximum power of multi-junction solar cell is achieved when the cell is placed on the focal plane of Fresnel lens. But it is proved to be incorrect by our research. When light beams of different wavelengths go through the Fresnel lens, their light spot distributions on the optical axis are not the same as those when they have different refractive indexes in Fresnel lens. At the same time, the triple-junction solar cell consists of three sub-cells which absorb light beams of different wavelengths respectively. Therefore, the performance of triple-junction cells would be influenced by the light distribution along the optical axis, this is exactly what we want to study in this work. The method of simulating the light tracing is used to calculate and analyze the light intensity distribution and non-uniform characteristics of different wavelengths of light concentrated by Fresnel lens. Combined with them from the circuit network model of a triple-junction solar cell, the electrical performances of triple-junction solar cell at different positions along the optical axis are studied. It is found from the simulation that the performance of cell does not reach the best state when cell is placed on the focal plane. The power of cell on the focal plane reaches only 0.41 W while the maximum point arrives at 0.69 W. The high non-uniformity of light on cell surface when cell is placed on the focal plane causes the decline of power. And an outdoor HCPV testing system with the ability to change the distance between Fresnel lens and the cell is conducted. The experimental results and the simulation results match well, therefore our simulation approach is verified. It shows that the module achieves the maximum power on either side of the focal plane, and the output power can increase more than 20% after optimization. It is a result after equilibrium between light intensity and uniformity on cell surface.

We have developed the theory for using the deflection of laser beams of various wavelengths to determine molecular and thermal diffusion coefficients in multicomponent mixtures. In the past, simultaneous determination of molecular and thermal diffusion coefficients have only been achieved for binaries. Our procedure is faster and more accurate than the current techniques to determine molecular diffusion coefficients. The analysis for an N-component mixture requires deflections from (N - 1) beams of different wavelengths. We show in an example that the molecular and thermal diffusion coefficients can be determined reliably in a ternary mixture.

Turbidity in a titration solution or dilution upon sample introduction causes systematic errors in automatic Spectrophotometric set-point titrations. The reduction of these errors with a factor of about 10 is realized by subtracting the signals of two light beams of different wave length which pass the same titration solution. The signal values both depend on the absorption of coloured substances (indicator) and on turbidity or dilution effects. Assuming that these effects are independent of the wave length and selecting wave lengths at which indicator absorbance differs greatly, subtraction of the signals leads to the elimination of said effects. As an illustration nMole amounts of sulphate were titrated in 80–90% aceton with a lead(II)-titrant using dithizone as indicator. The standard deviation was about 2%. A titration took 1–2 min.

The First World Congress on Industrial Process Tomography was held at the Palace Hotel, Buxton, Derbyshire from 14-17 April 1999. Over the four days, 130 delegates registered, of which about half were from the UK, one-third from continental Europe and the remainder from countries as diverse as China, Australia, USA, Canada, Brazil and Japan. Approximately one-quarter of the delegates were non-academic. Although this event was the first `World Congress', it followed on from two earlier series of conferences. These started in 1992 with the European Concerted Action on Process Tomography (ECAPT), which hosted four events across Europe. This was followed by the Engineering Foundation, which organized two conferences in the `Frontiers in Industrial Process Tomography' series, one in the US. Each meeting has seen a steady growth in interest in the subject, with more delegates from a wider range of countries and a greater participation by industry, reflecting the growing importance in the use of tomographic techniques to address industrial applications and solve industrial problems.

The circular dichroism manifested in the photoionization yields of the chiral molecule fenchone has been investigated using two laser beams of different wavelengths intersecting at 90 degrees. This allowed different two-colour ionization schemes to be investigated so that the circular dichroism contributions of each step in the multiphoton ionization process could be deduced. The results showed that the circular dichroism generated by a beam at a wavelength of 260 nm could be strongly influenced by the polarization state of a 520 nm beam propagating in a perpendicular direction. The asymmetry in the ion yields was found to change depending on whether the 520 nm beam was left or right circularly polarized, and if it was linear polarized in a direction parallel or perpendicular to the propagation direction of the 260 nm beam. The control exhibited by the direction of the linearly polarized light is attributed to an orientation dependence of the circular dichroism due to selective excitation of the isotropic ensemble by the 520 nm beam. By contrast, when both beams were circularly polarized, the dependence on the polarization direction of the 520 nm pulse is ascribed to either the interference between different ionization pathways or excitation of a chiral vibronic wavepacket in the molecule. These results are the first demonstration of chiroptical quantum control of total ion yields, showing in principle that all-optical enantio-sensitive chemical processing may be possible in the future.

Nonlinear mode coupling among two beams of different wavelength that copropagate in a bimodal highly birefringent optical fiber may lead to the effect of modal attraction. Under such circumstances, the modal distribution of light at a pump wavelength is replicated at the signal wavelength, nearly irrespective of the input mode excitation conditions of the signal.

We propose a technique for calculating the color separation gratings aimed at separating plane light beams of different wavelengths into different diffraction orders. The technique is based on a special-type optimization criterion. With this criterion, the problem of calculating the piecewise-constant grating profile is reduced to sequentially solving independent problems of optimization of the step heights. We derived an analytical expression for the profile of a color separation grating that generalizes the familiar analytical solutions. The criterion introduced is used to design a diffractive optical element (DOE) that generates required light beams when it is illuminated by different wavelengths. Design of color separation gratings able to separate three and five different wavelengths and DOEs to demultiplex and focus the two- and three-wavelength beams is presented.

Chlorophyll fluorescence for non-destructive measurement of flavonoids in broccoli

The range of applications for additive manufacturing is expanding quickly, including mass production of athletic footwear parts1, dental ceramics2 and aerospace components3 as well as fabrication of microfluidics4, medical devices5, and artificial organs6. The light-induced additive manufacturing techniques7 used are particularly successful owing to their high spatial and temporal control, but such techniques still share the common motifs of pointwise or layered generation, as do stereolithography8, laser powder bed fusion9, and continuous liquid interface production10 and its successors11,12. Volumetric 3D printing13-20 is the next step onward from sequential additive manufacturing methods. Here we introduce xolography, a dual colour technique using photoswitchable photoinitiators to induce local polymerization inside a confined monomer volume upon linear excitation by intersecting light beams of different wavelengths. We demonstrate this concept with a volumetric printer designed to generate three-dimensional objects with complex structural features as well as mechanical and optical functions. Compared to state-of-the-art volumetric printing methods, our technique has a resolution about ten times higher than computed axial lithography without feedback optimization, and a volume generation rate four to five orders of magnitude higher than two-photon photopolymerization. We expect this technology to transform rapid volumetric production for objects at the nanoscopic to macroscopic length scales.

Universal Particle Detector Experiment

We study the interaction of optical beams of different wavelengths, described by a two-component, two-dimensional (2D) nonlocal nonlinear Schrödinger (NLS) model. Using a multiscale expansion method the NLS model is asymptotically reduced to the completely integrable 2D Mel'nikov system, the soliton solutions of which are used to construct approximate dark-bright and antidark-bright soliton solutions of the original NLS model; the latter being unique to the nonlocal NLS system with no relevant counterparts in the local case. Direct numerical simulations show that, for sufficiently small amplitudes, both these types of soliton stripes do exist and propagate undistorted, in excellent agreement with the analytical predictions. Larger amplitude of these soliton stripes, when perturbed along the transverse direction, disintegrate either to filled vortex structures (the dark-bright solitons) or to radiation (the antidark-bright solitons).

Rapid increases in the computer processing power available per unit cost, as well as a growing hunger for multimedia (text, audio, and image) entertainment and processing has led to heightened interest in multilayer and other volume optical storage technologies.1 One such technology is 2-photon absorption-based storage.2,3,4 In this approach, writing or erasure takes place only at the intersection of 2 beams of different wavelengths, thus allowing independent addressing of any point within a 3-dimensional volume. As a bit oriented (rather than holographic) memory, a unique physical location is allocated for each data bit. If individual bits are stored, volumetric densities on the order of terabits/cm3 may be achievable, and parallel reading of the bits (e.g.-in planes or pages) can enable 100 Gb/s data transfer rates. The key principle behind 2-photon memories is the creation of a molecular change in the media by the simultaneous absorption of 2 photons from 2 different beams by the dopant molecule, as shown in Fig. 1(a). The localized change can store bits by changing the index of refraction, absorption, fluorescence, or the material’s electrical properties. In our system experiments so far we have utilized materials in which 2-photon excitation creates a new absorption peak and subsequent 1 or 2-photon illumination results in efficient fluorescence for readout. The broad readout absorption profile, and the high fluorescence efficiency enable the use of inexpensive, low power replay sources, including LEDs and filtered lamps. In addition to non-destructive memory recall, we have also demonstrated optically induced erasure, thus enabling random accessibility and erasure of bits. These two-photon 3-D memories are similar to the multilayer optical disk systems with the potential for simple media fabrication, many layers, parallel access for high data transfer rates, and low raw bit error rates (BER). As shown in Fig. 1(b), orthogonal intersection of the writing beams may be used, or if ultra-short (e.g.-<100 femtosecond) pulses are used, a counter-propagating arrangement10,5 is feasible. While single bits may be stored and recalled, parallel access of lines or planes of data is naturally accommodated in two-photon 3-D memories, to provide increased data transfer rates. Due to diffraction of the addressing beam as it propagates across the data image, there exists a tradeoff between the volumetric density of the memory and the parallelism, or data transfer rate.9

It is well known that arc welding of thin metallic sheets in difficult due to their easier distortion and deformation. On the other hand, in laser welding, such distortion and deformation is greatly reduced due to a smaller spot size and smaller heat input than in arc welding. Even in laser welding, thinner metallic sheets become more difficult to weld due to the loss of materials and the difficulty in supporting a shallow molten pool against evaporation and recoil pressure, leading to the formation of cut or drilled welds. In this study, therefore, lap welding characteristics of thin metallic sheets were investigated by utilizing combined beams or respective single beam of normal pulsed YAG laser and Q-switched SHG YAG laser. It was consequently found that the formation conditions for good lap welds in thin stainless steel sheets were broadened by using combined laser beams. Especially, lap welding of pure copper sheets was very difficult with single pulsed YAG laser; however, it was confirmed to be possible to weld them with combined laser beams of two different wavelengths in the air environment.

We study nonlinear mode coupling among two intense and copropagating beams of different wavelength in bimodal and high birefringence optical fibers. With the proper design of the bimodal fiber, we show that this process may lead to modal attraction, where the modal distribution of light at a pump wavelength is replicated at the signal wavelength, independently of the input mode excitation conditions of the signal. We analyse the dependence of the efficiency of the modal attraction process upon the input state of polarization of both the signal and the pump beams.

In this chapter, several beam combining architectures suitable for DE applications have been reported, and are divided into two distinct categories: incoherent beam combination (IBC) and coherent beam combination (CBC). The purpose of each method is to increase the far field intensity when brightness and power of a single fiber amplifier is limited. In IBC, an array of fiber lasers is superimposed in the far field without control of the relative spectra or phases of the different fibers. No brightness enhancement is obtained from this method, limiting the maximum intensity in the far field. Although such beam combining has been successfully demonstrated by the Navy [5], this approach is limited to propagation ranges on the order of a few kilometers. In spectral beam combining (SBC), a separate class of IBC, incoherent beams of different wavelengths are spatially overlapped to create a single output beam of multiple colors. The brightness of the propagating beam can be increased at the cost of increased spectral bandwidth. Similarly, SBC has the advantage of not requiring active phase control or mutual temporal coherence of the individual beams. Alternatively, coherent beam combining (CBC) schemes require proper phase, frequency, and polarization relationships for efficient beam combination. Overall, due to their brightness enhancements, for longer range and higher power/ intensity DE applications, SBC and CBC are potentially more appealing.