The slow axis (SA) divergence of 20% fill-factor, 980nm, laser diodes (LDs) have been investigated under short pulsed
(SP) and continuous (CW) operation. By analyzing the data collected under these two modes of operation, one finds that the SA divergence can be separated into two components: an intrinsic divergence and a thermally induced divergence. At low injected current and power, the intrinsic SA divergence is dominant while at high power their magnitudes are approximately equal. The thermal gradient across the broad stripe is negligible under SP operation and, the SA divergence increased at a much slower rate as a function of injected current, thereby increasing the brightness of the LD by 2X. SRL has redesigned microchannel coolers that remove the thermal gradient under CW operation thereby eliminating the thermally induced SA divergence resulting in LDs that are 2X brighter at 300W/bar.
High brightness, laser-diode bars are required for efficient coupling into small-core optical-fibers. Record power and
brightness results were achieved using 20% fill-factor, 980nm, 1cm-wide, 4mm cavity-length bars. Lifetimes of single
bars, operated CW at 200W and 20°C, exceed 1000hr. Due to superb thermal management, the power conversion
efficiency (PCE) exceeds 60% at 200W output power. Similar lifetime and PCE were obtained for a 3-bar stack
emitting 600W output power.
We address the use of transmission geometry volume holograms as depth-selective imaging elements in profilometry. We derive the point-spread function (PSF) of the volume holographic imaging system using volume diffraction theory and use the PSF to estimate depth resolution. Experimentally measured PSF and depth-selective images are presented to verify the theoretical predictions. Furthermore, we show that with prior knowledge of the object, depth resolution can be improved greatly with the method of inclined illumination. In more general cases, super resolution can also be achieved with digital post-processing methods such as Viterbi algorithm (VA). We show that computational complexity can be reduced with surface constraints. Resolution improvement by a factor of 5 was obtained in experimental demonstration.
Volume holographic imaging (VHI) utilizes the Bragg selectivity of volume holograms to achieve 3D optical slicing. The depth resolution of VHI degrades quadratically with increasing object distance like most 3D imaging systems. We have devised an imaging scheme that takes advantage of the superior lateral resolution of VHI and a-priori surface information about the object to build a profilometer that can resolve 50 μm features at a working distance of ≈ 50 cm. We discuss the scheme and present experimental results of surface profiles of MEMS devices.