Spectral Beam Research Articles

Simultaneous measurement of the absolute and relative time delay of a tiled-aperture coherent beam combination via the double-humped spectral beam interferometry.

Coherent beam combination (CBC) is a promising technology for achieving several hundred petawatts and even EW-level lasers. However, the measurement of the synchronization error and the time jitter of CBC is one of key technical issues, especially in the few-cycle PW-level laser facilities. In this paper, we demonstrate that the absolute time delay (ATD) and the relative time delay (RTD) for a tiled-aperture CBC can simultaneously be measured by using the double-humped spectral beam interferometry. The experimental study also was demonstrated. A root-mean-square deviation of approximately λ/38 (70 as) and a combining efficiency of 87.3% at 1 Hz closed feedback loop was obtained, respectively. Due to the wide adjustment range and a vast resisting beam energy disturbance capacity, this technique provide an effective and practical solution for measuring simultaneously the ATD and the RTD in the few-cycle PW-level laser pulses CBC.

Simulation and experimental study of laser-induced thermal deformation of spectral beam combination grating.

The multilayer dielectric (MLD) grating is a critical device for combining multiple laser beams into a single beam in a spectral beam combining (SBC) system. We established a theoretical thermal deformation model of the laser-irradiated MLD grating. Thermal deformation on the surface of the grating is simulated according to a series of parameters including the laser irradiation time, laser power density, and substrate size. To verify the model, we exposed a 960 l/mm, 50×50×1.5 mm3 grating to a laser power density of 3.61 kW/cm2 and observed the temperature change. We used a Twyman-Green interferometer to measure the interference fringes on the grating surface. Based on the Fourier-transform method and a Zernike polynomial fitting method, the real-time grating surface profile is reconstructed. The results show that substrate thickness increase or area decrease can reduce thermal deformation, the average decreases are 18.3% and 19.9%, respectively. The discussion and analysis of the grating thermal deformation are potentially valuable for designing grating to decrease the thermal deformation and improve the combined beam quality of a SBC system.

Organic luminescent down-shifting liquid beam splitters for hybrid photovoltaic-thermal (PVT) applications

Hybridised photovoltaic-thermal (PVT) systems, obtained by merging photo-voltaic (PV) and photo-thermal (PT) technologies, can lead to enhanced conversion efficiencies. Liquid spectral beam splitters (SBSs) offer control of the ‘thermal’ and ‘electrical’ components of the solar spectrum. Combining PVT systems with liquid SBSs facilitates enhanced control of the thermal and electrical outputs, further improving the PVT systems efficiency and making them economically viable. Traditionally, liquid SBSs contain nanostructures suspended in a base-fluid to capitalise on the enhanced heat transfer capabilities offered by the nanostructures' surface morphology. These nanofluids have certain disadvantages, such as stability problems, environmental hazards and synthetic cost concerns, which preclude them from becoming a viable substitute for commercial (single-phase) fluids. This study offers an alternative strategy by employing a set of newly developed fluids containing organic and organometallic imidazo[4,5-f][1,10]phenanthroline derivatives for SBS-PVT systems. These new working fluids were designed to mimic the behaviour of luminescent down-shifting (LDS) molecules while offering enhanced thermophysical characteristics over the host base-fluid. Their optical, fluorescent and thermophysical properties enabled an increased heating rate within the working fluid. Their integration as working fluids in an SBS-PVT system lead to optical efficiencies of ~63% i.e. an 18%–20% improvement over the standalone PV technology. The fluid properties displayed a 61% increase in the economic value of the energy captured when compared to the host base-fluid alone for the same PVT system. Consequently, these novel fluids and the organic molecules they contain can be effectively designed as high performance spectrally selective fluids for PVT applications.

Spectral Observation Theory and Beam Debroadening Algorithm for Atmospheric Radar

In order to measure the variance of wind velocity, which is contributed from turbulence, via radar observations, it is necessary to remove the unwanted contribution from strong horizontal velocity components through the finite beamwidth of the radar. This effect is referred to as beam broadening. Although the amount of beam broadening has thus far been calculated based on the approximating assumption that the pattern of the beam is rotationally symmetric and has very low sidelobes, we need to take a more theoretical approach to radar—one that does not have a simple beam pattern like the Antarctic Program of the Antarctic Syowa Station (PANSY) radar (69S, 39E). In this article, we clarify the theoretical relationship in a very simple form between the turbulence spectrum, which is directly associated with the variance of turbulence, two-way beam patterns, and the observed spectrum, using autocorrelation functions (ACFs). The theory is thoroughly universal and applicable to any type of atmospheric radar, such that we can quantitatively analyze radar observation systems. Furthermore, we propose a “debroadening” algorithm based directly on this theory and from calculations of the general maximum likelihood (ML). We performed numerical simulations that validate our theory and the algorithm.

High power, tunable, ultra-narrowband Yb-doped superfluorescent fiber source operating at wavelength less than 1055 nm with 20 nm tuning range

Tunable, narrowband superfluorescent fiber sources (SFSs) are significantly important for spectral combination. Here, we propose a high power, tunable, ultra-narrowband Yb-doped SFS operating at wavelength less than 1055 nm with 20 nm tuning range. The system is composed of a broadband SFS, a home-mode space-to-fiber tunable spectral filter, and a three-stage amplifier chain. In order to achieve three typical characteristics, namely, operating in the shorter wavelength region (SWR) with wide spectrum, tunable and narrowband, and high-power output, the performance of the system is investigated and optimized based on the rate equations with temperature, grating monochromator and the coupling theory of Gaussian beam between fibers. Theoretical investigation indicates that a broadband SFS operating in the SWR with wide spectrum can be achieved by controlling temperature within a certain range. Moreover, by optimizing space-to-fiber tunable spectral filter, the tunable, ultra-narrowband SFS with linewidth of 0.088 nm can be obtained. In addition, the seed laser with signal to noise ratio (SNR) of more than 30 dB and the appropriate length of active fiber can gain better amplification performance from the main amplifier. Based on these optimized parameters, a high power, tunable, ultra-narrowband Yb-doped SFS has been built experimentally. The output power of narrowband SFS operating in tunable range from 1035 nm to 1055 nm exceeds 300 W with M2 factor of 1.47, and the measured full width at half maximum and SNR of which are less than 0.1 nm and beyond 30 dB, respectively. This work extends the spectral region and capacity of narrowband SFSs, and will be useful for further power scaling of spectral beam combination.

Design of a Simply Structured High-efficiency Polarization-independent Multilayer Dielectric Grating for Spectral Beam Combining

Design of a Simply Structured High-efficiency Polarization-independent Multilayer Dielectric Grating for Spectral Beam Combining

A time-domain spectral element method with C1 continuity for static and dynamic analysis of frame structures

This paper presents a new C1-type beam spectral element method, which aims to ensure the continuity of the deflection and its first derivative at the junction of the adjacent spectral elements. The proposed method is based on the Euler-Bernoulli beam theory. The main novelty of the method is that two different sets of interpolation functions are adopted for the axial displacement and deflection in order to meet the C1 continuous requirement. By removing the rotational degrees of freedom of the internal nodes, a lumped mass matrix can be formed in this spectral element method. Static and dynamic analysis of various beams and frame structures are performed to examine the validity of the proposed spectral beam element model. The numerical results show that the proposed method is accurate and effective. A single element for each component of the structure is able to provide good results.

High temperature stability and optical properties investigation of a novel ITO-Therminol 66 nanofluid for spectral splitting PV/T systems

Abstract Spectral beam splitting technology based on optical nanofluids (NFs) is a promising field of solar energy research. However, the challenges to optimize the optical properties and enhance the high temperature stability of NFs are always exist. In this study, Indium Tin Oxide (ITO) nanoparticles were selected as the research object because of the excellent optical properties. The Oleylamine-capped ITO nanoparticles were prepared by chemical reduction. A novel NF based on Therminol 66 was successfully prepared. The high temperature stability and optical properties of obtained Oil-based NFs were analyzed by the gravitational sedimentation method and spectrophotometry. Moreover, we experimentally studied the effect of single reaction condition on the morphology and Sn-doping of particles. The results indicated that, at the reaction condition of 320 °C, 5.5 h, and the In/Sn mole ratio of 90:10, the obtained nanoparticles had high monodispersity and crystallinity, and the resulting NF had good stability and dispersion. Furthermore, when tuning single reaction condition, the morphology and Sn doping of nanoparticles tended to be a regular change. However, the change of single reaction condition was not enough to obtain the ITO NFs with good stability and dispersion. The ITO NFs obtained in present study had high thermal stability, and showed different high-temperature characteristics in the Ultraviolet and visible (UV–Vis) and near infrared (NIR) regions.

SIMULASI LENSA GRATING TERHADAP EFISIENSI DIFRAKSI GRATING PADA SISTEM PEMISAH CAHAYA SPEKTRAL CONCENTRATED PHOTOVOLTAIC/THERMAL

A spectral beam splitting concentrated photovoltaic/thermal (SBS CPVT) system is a new technology in PV areas . In order to split the sunlight, the grating lens is used in this study. The tool of this study is G-Solver software which simulates the diffraction efficiency of visible light and infrared light of the blazed and binary grating lens. The aim of this paper is to analyze the potential of the diffraction efficiency of grating lens when applied in SBS CPVT. The result show that binary grating, the highest diffraction efficiency for the visible light is also almost unchanged for the aspect ratio from 1.4 to 2, but the peak wavelength shift from around 360 nm to 510 nm, while, for IR light, the diffraction efficiency decrease from aspect ratio 1.4 to 2. On the other hand, blazed grating, The highest diffraction efficiency for the visible light is almost unchanged for the aspect ratio from 1.4 to 2, but the peak wavelengths shift from around 350 nm to 500 nm. While IR light, the diffraction efficiency decrease with the aspect ratio 1.4 to 2

Design and analysis of a concentrating PV/T system with nanofluid based spectral beam splitter and heat pipe cooling

Abstract This paper proposes a concentrating photovoltaic/thermal (CPV/T) system which combines the advantages of Ag/CoSO4-propylene glycol (PG) nanofluid based spectral beam splitter and heat pipe cooling technologies to enhance the solar energy conversion efficiency. A dynamical energy balance model for the designed CPV/T system to describe its electrical and thermal behavior is presented which was documented by few literatures. To provide theoretical guidance for further prototype design, the effects of concentration ratio, filter mass flow rate, water mass in both the water tank and the thermal collector, ambient temperature and wind speed on the all-day performance of the designed CPV/T system are discussed. Moreover, this work firstly studies the role of heat pipe cooling on nanofluid based spectral beam splitting system performance. Results show that when the concentration ratio varies from 1 to 8 suns, the average difference in system average total efficiency of heat pipe cooling mode and no heat pipe mode is 10.4%. Under the solar irradiance in a typical day with concentration ratio of 5 suns, the instantaneous total efficiency of the system reaches a maximum value of 73.20% at 17: 00 with 7.55% coming from electricity and its average total efficiency for the whole day is 53.66%.

Investigation effect of a spectral beam splitter on performance of a hybrid CPV/Stirling/TEG solar power system

The augmentation of clean energy production in energy policy and planning is an important object for most countries. Hence enhancement of power generation from renewable and sustainable energies such as solar energy has been considered by many researchers. In this study, a novel combination of concentrated photovoltaic (CPV), Stirling engine, and thermoelectric generators (TEGs) is simulated theoretically by Engineering Equation Solver (EES) software. Moreover, a novel TEG heat exchanger used to harvest energy from rejected heat of the Stirling engine, while it doesn't have any adverse effect on performance of the Stirling engine. Since both of Stirling engine and CPV have high efficiency in some conditions, determining the contribution of input energy to each section is essential to achieve maximum performance of the system. Therefore, investigation of beam splitter's cut-off wavelength to determine the best energy efficiency for the proposed system is the main object in the present study. The results show that the best performance of the proposed system is achieved within 875 nm cut-off wavelength of the beam splitter. Also, TEG modules could harvest approximately 400 W from rejected heat of the Stirling engine.

Nanosecond illumination source for speckle-free liquid crystalmicroscopy

ABSTRACT We present a setup for the speckle-free, low-light microscopy imaging at ~5 ns exposure times. The design is based on stroboscopic principle and uses fast and incoherent fluorescent emission from a dye, excited by a picosecond laser pulse. The basic spatial, spectral, and temporal beam properties are characterised, modelled and compared for two different designs of the source: (i) Rhodamine 6 G dye dissolved in ethanol and put in a glass cuvette, and (ii) random laser based on the dispersion of 300 nm TiO2 nanospheres in an ethanol solution of Rhodamine 6 G dye. The proposed solution of Rhodamine 6 G dye in ethanol put in a glass cuvette gives an excellent image quality with high contrast, excellent stability and tunable coherence. It delivers ~30 nJ of completely incoherent light per excitation laser pulse energy of ~40 μJ. It allows for the photographic measurements with 5 ns exposure time, demonstrated in imaging of thermally quenched 5CB liquid crystal. The set-up is used in studies of Kibble-Zurek mechanism of topological defect nucleation and growth at sub-microsecond time resolution and extremely fast cooling rates of ~40,000 K/s.

Investigation of the Efficiency of Spectral Beam Combining of Laser Diode Array in a Cavity with the Spectrally Selective Output Coupler

We investigate the operating modes of diode lasers in the external cavity scheme of spectral beam combining, using the virtual laser-diode array method. We determine the spectral range of the diode array and the watt–ampere characteristics of a single-diode laser for various wavelengths. We experimentally show that by varying the output coupler transmission with the wavelength, one can optimize the generation power of laser diodes in the array and force it to work in different regions of the gain bandwidth of the active medium.

Lasing Characteristics of Single-Mode Laser Diode Arrays at Spectral Combining of Beams

Lasing of an array of 30 single-mode laser diodes with different wavelengths is experimentally investigated in the scheme of spectral beam combining. The maximum lasing power of 7.2 W is obtained in the pulsed mode with the quality of the combined beam close that of a single diode at the total lasing spectrum width of about 40 nm and the spectral component line widths below 0.3 nm.

High power microsecond fiber laser at 1.5 μm.

In this work, we demonstrate a single frequency, high power fiber-laser system, operating at 1550 nm, generating controllable rectangular-shape μs pulses. In order to control the amplified spontaneous emission content, and overcome the undesirable pulse steepening during the amplification, a new method with two seed sources operating at 1550 nm and 1560 nm are used in this system. The output power is about 35 W in CW mode, and the peak power is around 32 W in the pulsed mode. The repetition rate of the system is tunable between 50 Hz to 10 kHz, and the pulse duration is adjustable from 10 μs to 100 μs, with all on the fly electronically configurable design. The system demonstrates excellent long and short time stability, as well as spectral and spatial beam quality.

Effect of thermal errors of a transform lens on beam properties in spectral beam combining systems

Thermal errors of the transform lens are characterized by surface deformation, position shift and extra aberration. A beam propagation model is further proposed by the ray trace method. Beam properties such as intensity distribution, beam quality, and spectrum have been analyzed. Results show that the surface deformation degrades obviously beam quality and broadens the spectrum of the combined beam. The position shift affects the intensity peak, and also degrades beam quality. Side lobes of the combined beam become increasingly obvious due to the growing extra aberration. A movable platform and a spatial filter are suggested to optimize combined beams.

Accurate temperature measurement of a spectral beam combination grating based on VO2 film.

In a spectral beam combination system, temperature increase of the multilayer dielectric grating (MDG) worsens the far-field beam quality of the output laser. To accurately monitor the surface temperature of the MDG, this study deposits VO2 phase-change film on the lowest layer of multilayer dielectric films in the MDG and tests the transmittance with a probe laser. Based on this measurement, the surface temperature of the MDG can be calculated. Additionally, the study analyzes the influence of VO2 film on the surface electric field and the -1 diffraction efficiency of the MDG and presents a specific example of using VO2 film to test high reflector temperature. The study concludes that VO2 film is a feasible method of measuring temperature and better than an infrared thermal imager.

High-Efficiency Spectral-Beam-Combined 930nm Diode Laser Source**Supported by the National Natural Science Foundation of China under Grant No. 61535013.

Spectral beam combining is an effective way to achieve high-brightness direct diode laser output. We present an experimental study on spectral beam combining with external cavity based on transmission grating. Using a series of cylindrical transform lenses with different focal lengths, spectral beaming combining efficiency is greatly improved, and the results of wavelength intervals are consistent with the theoretical calculations. With the injection current of 90 A, a 75.1 W cw 930 nm output power with wavelength span of 18.6 nm and spectral beam combining efficiency of 92.7% is achieved, the beam parameter product is 5.77 mm⋅mrad.

Design and thermodynamic analysis of a novel solar CPV and thermal combined system utilizing spectral beam splitter

A novel solar concentrating PV and thermal (CPVT) combined system with beam splitter and compact concentrator structure is proposed in this study. The system structure and its design method are provided. The optical filter is designed and the incident light angle effect on the beam splitting performance is investigated. Solar concentrating simulations are conducted and the relevant results reveal that the CPVT combined system can provide a high solar concentration uniformity. The evaluation results of configuration and optical analyses indicate that when all the other parameters are settled, the optimal installation height of the solar receiver tube is 923.0 mm. The influence study of sun tracking accuracy on the system optical performance is launched. It is concluded that when the tracking error increases to 1.0°, the overall optical efficiency is 66.2%. The thermodynamic analysis results indicate that the PV conversion and overall energy efficiencies of the CPVT system are 30.5% and 26.6%, which are both higher than those of the normal CPV system. Moreover, the operating temperature effect investigation of solar thermal receiver tube is conducted. The results show that an optimal solar thermal receiver tube temperature (356.0 °C) exists, which can result in the maximum total output power.

Spectral beam splitting retrofit for hybrid PV/T using existing parabolic trough power plants for enhanced power output

Conversion of sunlight into electricity is the fastest growing commercial means of deploying renewable energy at utility scale. The two primary methods for conversion are photovoltaics and concentrating solar thermal power. The complimentary advantages of these two methods motivates interest in hybridizing the two. Here, a spectral beam splitting approach is designed and tested for application as a retrofit in existing parabolic trough concentrating solar power facilities, the first large scale test using such an approach with low-cost silicon photovoltaic cells. Such an approach leverages the existing capital cost of the plant with the potential to boost plant output. The novel on-sun testing here focused on the electrical performance of a silicon photovoltaic module integrated into the most common parabolic trough geometry with a net aperture area of 1.7 m2. The spectral beam splitter has a solar weighted reflectance of 71.2%, and delivered an average flux to the cells of 17,828 W/m2 representing a concentration ratio of 25×, within 10% of the prediction of the optical ray tracing model. The two photovoltaic modules achieved an average efficiency - based upon measured irradiance delivered to the cells - of 12.4% (or 3% if normalized to the total aperture of the area of the mirror). A corresponding decrease in thermal performance was observed when the retrofit was added. Overall the design is capable of providing a path to retrofit existing parabolic trough powerplants to provide a 13% increase in power output using commercially available photovoltaic technology.