Beam-combinable, high-power, narrow-linewidth Yb-doped fiber amplifiers are presently being evaluated as high energy laser weapons where the rapid turn-on of the amplifiers is critical. These amplifiers are optically pumped at the narrow 976nm, high-absorption peak of ytterbium. The fiber amplifier turns on when the emission spectra of the diode pump modules significantly overlap the 976nm Yb absorption peak. The thermal wavelength tuning behavior of two types of laser diode sources was analyzed to predict the cold-start turn-on-time of a fiber amplifier. Turn-on-times of ~4ms and ~4s were predicted for a fiber amplifier employing a laser diode bar directly attached to a micro-channel cooler and a single emitter package cooled by a cold plate, respectively.

The Compressed Baryonic Matter (CBM) Experiment will be one of the major scientific endeavors of the future Facility of Antiproton and Ion Research (FAIR) in Darmstadt. Nuclear collisions at an interaction rate of up to 10 MHz will provide the data for numerous observables, including rare probes with necessary statistical significance. Key to achieve this goal is a fast and radiation hard detector subsystem for particle tracking. In the CBM experiment, the Silicon Tracking System (STS) is the main system for particle tracking. Signal read-out from the 2x1024 channel sensors is based on the self-triggering STS-XYTERv2 ASIC specifically developed for this application. Towards final STS-operation, a down-scaled mini-CBM (mCBM) setup was taken into operation at the SIS18 accelerator at GSI. In this paper, the test measurements of the STS-XYTERv2 asıcs and operational tests performed for quality assurance during the assembly of the mSTS detector modules will be presented and discussed in detail. These measurement procedures will constitute fundamental processes for quality assurance (QA) in the assembly of the roughly 900 STS detector modules.

In the most developed fiber amplifiers, optical pump power is introduced into the similar to 400 mu m-diameter, 0.46NA first cladding of the double-clad, Yb- doped, gain fiber, using a (6+1):1 multi-mode fiber combiner. For this configuration, the core diameter and numerical aperture of the pump delivery fibers have maximum values of similar to 225 mu m and similar to 0.22, respectively. This paper presents the first fiber-coupled laser-diode pump module emitting more than 1kW of cladding-mode-stripped power from a detachable 225 mu m, 0.22NA delivery fiber at 976nm. The electrical-to-optical power conversion efficiency at 1kW is similar to 50%. The FWHM spectral width at 1kW output is similar to 4nm and has an excellent overlap with the narrow absorption spectrum of ytterbium in glass. Six of these pump modules attached to a (6+1): 1 multimode combiner enable a 5-6kW, single-mode, Yb-doped fiber amplifier.

We present a fiber-coupled pump-module emitting more than 1kW of mode-stripped power at 976nm from a detachable 225µm, 0.22NA fiber. The electrical-to-optical efficiency at 1kW is ~50%. Six of these pump modules attached to a (6 + 1):1 multimode combiner enable a 5-6kW, single-mode, Yb-doped fiber amplifier.

In this paper, we present hybrid assembly technology to maximize coupling efficiency for spatially combined laser systems. High quality components, such as center-turned focusing units, as well as suitable assembly strategies are necessary to obtain highest possible output ratios. Alignment strategies are challenging tasks due to their complexity and sensitivity. Especially in low-volume production fully automated systems are economically at a disadvantage, as operator experience is often expensive. However reproducibility and quality of automatically assembled systems can be superior. Therefore automated and manual assembly techniques are combined to obtain high coupling efficiency while preserving maximum flexibility. The paper will describe necessary equipment and software to enable hybrid assembly processes. Micromanipulator technology with high step-resolution and six degrees of freedom provide a large number of possible evaluation points. Automated algorithms are necess ary to speed-up data gathering and alignment to efficiently utilize available granularity for manual assembly processes. Furthermore, an engineering environment is presented to enable rapid prototyping of automation tasks with simultaneous data ev aluation. Integration with simulation environments, e.g. Zemax, allows the verification of assembly strategies in advance. Data driven decision making ensures constant high quality, documents the assembly process and is a basis for further improvement. The hybrid assembly technology has been applied on several applications for efficiencies above 80% and will be discussed in this paper. High level coupling efficiency has been achieved with minimized assembly as a result of semi-automated alignment. This paper will focus on hybrid automation for optimizing and attaching turning mirrors and collimation lenses.

Dense arrays of single-mode slab-coupled optical waveguide lasers with a pitch of 40 μm have achieved 483 W from a single 1 cm wide bar.

We present a novel, high-power stack of 20% fill-factor, 976nm, laser-diode bars, each directly attached to an enhanced lateral-flow (ELF), copper-based, water-cooled heat-sink. The heat-sinks contain mounting screws that form a kinematic mount to minimize detrimental mechanical-stress on the diode bars while also providing beneficial, double-side cooling of the bars. A stack of 18-bars, emitting 2.54kW, was constructed to validate the technology. Using standard optics and a polarization multiplexer, a 320μm diameter, 0.3NA focus is achieved with a 6-bar stack that robustly couples 450W, with a ~67% coupling efficiency, from a passive, 400μm, 046NA doubleclad fiber.

Current dependent absorption in broad area edge emitting lasers has been measured using laser diodes with high reflectivity (HR) output facets.

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 degrees 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.

A record, 250W, CW output-power has been achieved for a single, 1cm-wide, 3.5mm cavity-length, 20% fill-factor, 976nm, laser-diode bar operated at 20 degrees C. The remarkable laser-bar performance was in part the result of a novel EPIC (Enhanced Performance Impingement Cooler) heat-sink with a thermal resistance of 0.16K/W. The superb thermal management resulted in record brightness for a laser bar, i.e. a slow-axis divergence of 10 (95% power containment angle) was achieved at 200W output-power. A coupling efficiency of similar to 74% into a 200 mu m core, 0.22NA fiber was achieved.

Fluorescence microscopy is an essential tool in modern biological research. It is a powerful method that allows noninvasive monitoring of specifically labeled targets within living cells, and simultaneous detection of multiple targets using different labels. The spatial resolution in fluorescence microscopy is limited because of the diffraction limit; the resolution in transverse direction is proportional to λ/2NA = λ/2nsinθ (where n is the refractive index in the object space, and θ is the half-angle of the largest cone of rays that can enter or leave the optical system), whereas the longitudinal resolution is given by 2λn/NA2. High-spatial resolution to detect fluorescent molecules below the diffraction limit can be achieved in several ways, such as by increasing the effective numerical aperture (as in 4Pi confocal microscopy) [1], introducing spatial variation in the excitation light creating finer spatial features in the image (as in standing wave microscopy) [2], using multiple-photon fluorescence absorption or emission mechanisms that lead to nonlinear effects in the light field (as in 2-photon microscopy) [3], and by selectively quenching the fluorescence from a focal spot to obtain a very small fluorescing volume (as in stimulated emission depletion microscopy) [4].

We theoretically study the problem of detecting dipole radiation in a fiber-based confocal microscope of high numerical aperture. By using a single-mode fiber, in contrast to a hard-stop pinhole aperture, the detector becomes sensitive to the phase of the field amplitude. We find that the maximum in collection efficiency of the dipole radiation does not coincide with the optimum resolution for the light-gathering instrument. The derived expressions are important for analyzing fiber-based confocal microscope performance in fluorescence and spectroscopic studies of single molecules and/or quantum dots.

Spontaneous emission of fluorophores located close to a reflecting surface is modified by the interference between direct and reflected waves. The spectral patterns of fluorescent emission near reflecting surfaces can be precisely described with a classical model that considers the relative intensity and polarization state of direct and reflected waves depending on dipole orientation. An algorithm based on the emission model and polynomial fitting built into a software application can be used for fast and efficient analysis of self-interference spectra, yielding information about the location of the emitters with subnanometer precision. Spectral information was used to study thin films of fluorescent substances on surfaces.

In this work we examine two general approaches to subsurface imaging, the first using solid immersion lens technology to optimize the numerical aperture and the second an interferometric spectral fluorescence technique for buried emitters