Abstract. The performance of a multisection DBR semiconductor laser emitting around 1.06 µm is experimentally and theoretically investigated. A thermal-induced change of the refractive index implied by an increase of the injection current yields nearly-periodic transitions between neighboring cavity modes. These transitions are explained by means of a modal analysis and and by numerical simulations based on the traveling wave model.
Wavelength-stabilized compact laser systems at 670 nm on a micro-optical bench are presented. The resonator concept consists of a tapered semiconductor gain medium and a reflection Bragg grating as a wavelength selective resonator mirror. In pulse operation mode with 100 ns pulses, an optical peak power of 5 W with a spectral width below 150 pm was achieved. Nearly diffraction-limited beam quality at optical output powers up to 1 W is obtained. Such laser systems can be used, e.g., for Raman spectroscopy and as pumping sources for frequency conversion toward UV spectral range.
Redistribution of LED radiation in lighting is necessary in many applications. In this article, we propose a new optical component design for LED lighting to achieve a higher performance. The design consists of a commercial collimator and two linear Fresnel lenses. The LED radiation is collimated by a collimator and redistributed by double linear Fresnel lenses to create a square-shaped, uniform distribution. The linear Fresnel lenses design is based on Snell’s law and the “edge-ray principle”. The optical devices are made from poly methyl methacrylate (PMMA) using a high-speed computer numerical control (CNC) machine. The LED prototypes with complementary optics were measured, and the optical intensity distribution was evaluated. The numerical results showed we obtained a free-form lens that produced an illumination uniformity of 78% with an efficiency of 77%. We used the developed LED light sources for field experiments in agricultural lighting. The figures of these tests showed positive effects with control flowering criteria and advantages of harvested products in comparison with the conventional LED sources. This allows our approach in this paper to be considered as an alternative candidate for highly efficient and energy-saving LED lighting applications.
The thermal properties and the degradation behavior of high-power broad-area diode lasers emitting at 650nm are analyzed. Imaging thermography is applied to assess the bulk temperature while the facet temperature is measured by micro-Raman spectroscopy. Although no visible facet alteration is observed, power degradation is found to be accompanied by increased temperatures at the facets. The immediate vicinity of them also turns out to be the starting point for the creation of defect networks within the quantum well seen in cathodoluminescence images. The observed behavior is compared to that known for near-infrared emitting devices.
A methodological approach to strain analysis in semiconductor devices is presented. Two methods, degree-of-polarization of photoluminescence and photocurrent spectroscopy, are compared by analyzing a spatially inhomogeneous strained test sample, namely, a high-power diode laser array that is affected by packaging-induced stress. Both methods concordantly reveal a −0.1% uniaxial compression in the vicinity of the midpoint of the active region of the device, demonstrating the compatibility of and justifying the assumptions involved in the two different approaches. Furthermore, we discuss some distinctive details of the processing-induced strains observed in the vicinities of metallized contacts and grooves involved in the device design.
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