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One aspect of the present disclosure relates to an inspection system, in particular a mobile inspection system, for outdoor inspection of photovoltaic modules in situ, the inspection system comprising a movable detector unit and a processing unit; wherein the detector unit is configured to obtain, when positioned at a user‐controllable position spaced apart from a photovoltaic module of a photovoltaic power system, luminescence data from a light‐receiving surface of said photovoltaic module; the detector unit comprising: a light source, in particular a laser source, configured to emit an illumination beam; means for selectively directing the illumination beam onto respective portions of the light‐receiving surface so as, when the illumination beam is directed onto a first portion of the light‐receiving surface, to only illuminate the first portion while leaving a corresponding first remaining portion of the light‐receiving surface unilluminated by the illumination beam and, when the illumination beam is directed onto a second portion of the light‐receiving surface, to only illuminate the second portion while leaving a corresponding second remaining portion of the light‐ receiving surface unilluminated by the illumination beam; an imaging system configured to capture a plurality of images of the light‐receiving surface, the plurality of images including a first image captured while only the first portion is illuminated by the illumination beam and depicting at least a part of the first illuminated portion and at least a part of the unilluminated first remaining portion, the plurality of images further including a second image captured while only the second portion is illuminated by the illumination beam and depicting at least a part of the second illuminated portion and at least a part of the unilluminated second remaining portion; wherein the processing unit is configured to process the plurality of images to provide reconstructed image data indicative of lumines

4H-silicon carbide (SiC) integrated platforms have shown great potential in quantum and nonlinear photonics. However, the thermal properties of 4H-SiC waveguides are still unknown, even though thermo-optic effects can play an important role in fundamental measurements and practical applications. In this paper, we comprehensively study the thermo-optic effects in a 4H-SiC microring resonator, by means of both temperature tuning and self heating. The thermo-optic coefficient and the ratio between the thermal absorption and the thermal diffusion of 4H-SiC are quantitatively measured to be 4.21 × 10−5 K−1 and 14.9 K W-1, respectively. Taking the acquired thermal properties into account, we experimentally achieve Kerr-nonlinearity based dual-pump optical parametric oscillation (OPO), and thus demonstrate that broadband solitons could feasibly be generated through thermal tuning of 4H-SiC-oninsulator (SiCOI) microring resonators.

We report four-wave mixing with different polarization and spatial modes in a single 4H-silicon carbide photonic device. Our device shows great potential to perform high-dimensional multiplexing for optical communication and highdimensional entanglement in quantum networks. We use a polarization insensitive grating coupler and a multimode microring resonator that supports three polarization and spatial mode resonances. Finally, we show the polarization dependence of the third-order nonlinearity of 4H-silicon carbide. The measured nonlinear refractive index of the light polarized along the extraordinary axis, which is n2,TM=(13.1±0.7)×10−19m2/W, is twice as large as that of the light polarized along the ordinary plane, n2,TE=(7.0 ± 0.3)×10−19 m2/W, indicating that the extraordinary polarization is more efficient for nonlinear experiments in the 4H-silicon carbide integrated platforms as compared to the ordinary polarization.

A novel compact micro-integrated high-power narrow-linewidth external-cavity diode laser around 808 nm is demonstrated. The laser system contains a tapered amplifier consisting of a ridge-waveguide section and a tapered section with separated electrical contacts. Thus, the injection currents to both sections can be controlled independently. An external volume Bragg grating is utilized for spectral narrowing and stabilization. The diode laser system is integrated on a 5 mm x 13 mm aluminum nitride micro-optical bench on a conduction cooled package mount with a footprint of 25 mm x 25 mm. The diode laser system is characterized by measuring the output power and spectrum with the injection currents to the ridge-waveguide section (IRW) and tapered amplifier section (ITA) changed in steps of 25 and 50 mA, respectively. At IRW = 200 mA and ITA = 6.0 A, 3.5 watts of output power is obtained with an emission spectral linewidth with an upper bound of 6 pm, and a beam propagation factor in the slow axis, M2, of 2.6 (1/e2). The characterization of the temperature stabilization of the laser system shows an increase of the wavelength at a rate of 6.5 pm/K, typical for the applied volume Bragg grating. © 2019 Optical Society of America

In this chapter, both blue and green high-power tunable diode laser systems based on GaN broad-area diode laser (BAL) in Littrow external cavity are demonstrated. For blue diode laser system, for high-power application, an output power around 530 mW over a 1.4 nm tunable range is obtained; for wide tunable range application, an output power around 80 mW over a 6.0 nm tunable range is obtained. For the green diode laser system, for high-power application, an output power around 480 mW with a tunable range of 2.1 nm is achieved; for wide tunable range application, an output power of 50 mW with a tunable range of 9.2 nm is achieved. The tuning range and output power optimization of an external-cavity diode laser system is investigated based on the experimental results obtained in the blue and green external-cavity GaN diode laser systems. The obtained results can be used as a guide for selecting gratings for external-cavity diode lasers for different requirements. The temporal dynamics of the green diode laser system is studied experimentally, and pulse package oscillation is observed, for the first time to our knowledge, in a BAL with an external-cavity grating feedback.

Although external-cavity feedback with a grating is widely used to achieve a tunable high-power narrow-linewidth broad-area diode laser (BAL) system, the dynamics of such a system is seldom studied. In this paper, the temporal dynamics of a tunable high-power green external-cavity diode laser system based on a GaN BAL and Littrow external-cavity is investigated experimentally. The regular pulse package oscillation (PPO) is observed just above the threshold. The oscillating period of the pulse package decreases with the increasing injected current. As the current increases further, the pulse package oscillates irregularly, and finally changes to a chaotic state. The PPO is observed, for the first time to our knowledge, in a BAL with an external-cavity grating feedback.

Diffuse optical tomography (DOT) is a reliable and widespread technique for monitoring qualitative changes in absorption inside highly scattering media. It has been shown, however, that acousto-optic (AO) imaging can provide significantly more qualitative information without the need for inversion algorithms due to the spatial resolution afforded by ultrasound probing. In this Letter, we show how, by using multiple-wavelength AO imaging, it is also possible to perform quantitative measurements of absorber concentration inside scattering media. (C) 2018 Optical Society of America

In this chapter, both blue and green high-power tunable diode laser systems based on GaN broad-area diode laser (BAL) in Littrow external cavity are demonstrated. For blue diode laser system, for high-power application, an output power around 530 mW over a 1.4 nm tunable range is obtained; for wide tunable range application, an output power around 80 mW over a 6.0 nm tunable range is obtained. For the green diode laser system, for high-power application, an output power around 480 mW with a tunable range of 2.1 nm is achieved; for wide tunable range application, an output power of 50 mW with a tunable range of 9.2 nm is achieved. The tuning range and output power optimization of an external-cavity diode laser system is investigated based on the experimental results obtained in the blue and green external-cavity GaN diode laser systems. The obtained results can be used as a guide for selecting gratings for external-cavity diode lasers for different requirements. The temporal dynamics of the green diode laser system is studied experimentally, and pulse package oscillation is observed, for the first time to our knowledge, in a BAL with an external-cavity grating feedback.

The results of photoluminescence (PL) imaging performed with a laser line scan in a prototype setup are presented in this work. Here we show the PL images with the photovoltaic cell positioned at different distances from the laser line source, therefore with the beam at different intensities and line characteristics. This study is motivated by the time demanding process of acquiring luminescence images for accurate PV inspections in the field, usually made with electroluminescence imaging. The PL imaging induced by a laser line has the potential to be compact enough to be portable and carried out by drones for field inspections.

In this paper we discuss how different feedback gratings affect the tuning range and the output power of external feedback diode laser systems. A tunable high-power narrow-spectrum external-cavity diode laser system around 455 nm is investigated. The laser system is based on a high-power GaN diode laser in a Littrow external-cavity. Both a holographic diffraction grating and a ruled diffraction grating are used as feedback elements in the external cavity. The output power, spectral bandwidth, and tunable range of the external cavity diode laser system are measured and compared with the two gratings at different injected currents. When the holographic grating is used, the laser system can be tuned over a range of 1.4 nm with an output power around 530 mW. When the ruled grating is used, the laser system can be tuned over a range of 6.0 nm with an output power around 80 mW. The results can be used as a guide for selecting gratings for external-cavity diode lasers for different requirements. (C) 2016 Optical Society of America

In this paper, we investigate the dynamics of a BAL with lateral-mode selected external feedback experimentally by measuring the far-field profile, intensity noise spectrum and time series of the output beam. The mode-selection is achieved by adjusting a stripe mirror at the pseudo far-field plane. Different dynamic behaviors are observed when different lateral modes are selected. When the mirror is aligned correctly and high-order modes are selected, in most of the cases periodic dynamics of the output power corresponding to a single roundtrip external-cavity loop is observed, but the dynamic behavior disappears in some case; when the zero-order mode is selected, periodic dynamics corresponding to a double roundtrip external-cavity loop is observed. When the stripe mirror is not aligned perfectly, a dynamic behavior like pulse-package oscillations is observed: a periodic oscillated output with a frequency of the single roundtrip external-cavity loop modulated by periodic low-frequency fluctuation. This is the first observation of pulse-package oscillation in a diode laser with long-cavity feedback, to our knowledge.

Spectral properties, both the optical spectrum and the intensity noise spectrum, of a broad-area diode laser with off-axis external-cavity feedback are presented. We show that the optical spectrum of the diode laser system is shifted to longer wavelengths due to the external-cavity feedback. The intensity noise spectrum of the diode laser shows that the intensity noise is increased strongly by the external-cavity feedback. External-cavity modes are excited in the external cavity even in the off-axis configuration. The peak spacing of the intensity noise spectrum shows that single roundtrip external-cavity modes are excited. We believe that the four-wave mixing process in the broad-area diode laser is responsible for the establishment of the external-cavity mode.

The effect of external feedback on the degradation of 808 nm emitting AlGaAs-based high-power broad-area diode lasers is studied. For this purpose, early stages of gradual degradation are induced by accelerated aging at high power levels. While the quantum well that actually experiences the highest total optical load remains unaffected, severe impact by point defects is observed on the cladding layers and the waveguide. Extended defects such as dislocations, however, are not observed in such early stages of degradation, which are accompanied by gradual power loss of a few percent only.

A dual-wavelength high-power semiconductor laser system based on a tapered amplifier with double-Littrow external cavity is demonstrated around 800 nm. The two wavelengths can be tuned individually, and the frequency difference of the two wavelengths is tunable from 0.5 to 10.0 THz. To our knowledge, this is the broadest tuning range of the frequency difference from a dual-wavelength diode laser system. The spectrum, output power, and beam quality of the diode laser system are characterized. The power stability of each wavelength is measured, and the power fluctuations of the two wavelengths are almost of opposite phase. The simultaneous emission of the two wavelengths is verified by a sum-frequency generation experiment in a bismuth triborate nonlinear crystal.