A translatory MOEMS actuator with extraordinarily large stroke - especially developed for fast optical path-length modulation in miniaturized FT-spectrometers (FTS) designed for NIR spectral region (800 nm – 2500 nm) - is presented. A precise translational out-of-plane oscillation at 260 Hz with a stroke of up to 700 μm and minimized dynamic mirror deformation of 80 nm is realized by means of an optimized MEMS design. The MOEMS device is driven electro-statically near resonance and is manufactured in a CMOS-compatible SOI process. Due to the significant viscous gas damping, dominated by the drag resistance of the comparatively large mirror plate with 5mm diameter, the resonant MEMS device has to operate under reduced pressure. A mirror stroke of 700 μm at a driving voltage of 4V is achieved by hermetic encapsulation of the actuator at at a maximal pressure of 3.2 Pa. For FTS system integration the MOEMS actuator has been encapsulated in an optical vacuum wafer-level package (VWLP) to guarantee a long-term stable vacuum pressure of 0.1 Pa and lifetime t ≥ 10a.
Diode lasers are gaining importance, making their way to higher output powers along with improved BPP. The assembly of micro-optics for diode laser systems goes along with the highest requirements regarding assembly precision. Assembly costs for micro-optics are driven by the requirements regarding alignment in a submicron and the corresponding challenges induced by adhesive bonding. For micro-optic assembly tasks a major challenge in adhesive bonding at highest precision level is the fact, that the bonding process is irreversible. Accordingly, the first bonding attempt needs to be successful. Today’s UV-curing adhesives inherit shrinkage effects crucial for submicron tolerances of e.g. FACs. The impact of the shrinkage effects can be tackled by a suitable bonding area design, such as minimal adhesive gaps and an adapted shrinkage offset value for the specific assembly parameters. Compensating shrinkage effects is difficult, as the shrinkage of UV-curing adhesives is not constant between two different lots and varies even over the storage period even under ideal circumstances as first test results indicate. An up-to-date characterization of the adhesive appears necessary for maximum precision in optics assembly to reach highest output yields, minimal tolerances and ideal beamshaping results. Therefore, a measurement setup to precisely determine the up-to-date level of shrinkage has been setup. The goal is to provide necessary information on current shrinkage to the operator or assembly cell to adjust the compensation offset on a daily basis. Impacts of this information are expected to be an improved beam shaping result and a first-time-right production.
Single-mode-emitting high-power diode laser arrays (SM-HPDLA) are available industrially with more than 50 W
emission power per bar. Based on this platform an expandable prototype solution is realized for fiber coupling of a
stacked array with more than 100 W to an optical fiber with diameter of 200 micron and NA of 0.11. Advanced methods
of controlled assembly of micro-optics by infrared laser-soldering have been developed therefore. We present a compact
and scalable concept with scalability on 2 internal and 2 external factors. Internal factors are the increasing beam quality
and power stability of high-power single-mode-emitting arrays and the improved assembly accuracy for diode bar and
micro-optics. External factors are the interlaced coupling of stacked beam emission from the stacked array and the
further option to use optimized polarisation coupling with several diode laser stacks.
We introduce a method for noninvasively measuring muscle contraction in vivo, based on near-infrared diffusing-wave spectroscopy (DWS). The method exploits the information about time-dependent shear motions within the contracting muscle that are contained in the temporal autocorrelation function g(1)(,t) of the multiply scattered light field measured as a function of lag time, , and time after stimulus, t. The analysis of g(1)(,t) measured on the human M. biceps brachii during repetitive electrical stimulation, using optical properties measured with time-resolved reflectance spectroscopy, shows that the tissue dynamics giving rise to the speckle fluctuations can be described by a combination of diffusion and shearing. The evolution of the tissue Cauchy strain e(t) shows a strong correlation with the force, indicating that a significant part of the shear observed with DWS is due to muscle contraction. The evolution of the DWS decay time shows quantitative differences between the M. biceps brachii and the M. gastrocnemius, suggesting that DWS allows to discriminate contraction of fast- and slow-twitch muscle fibers.
Changes in scalp and cortical blood flow induced by voluntary hyperventilation are investigated by near-infrared
diffusing-wave spectroscopy. The temporal intensity autocorrelation function g(2) (τ) of multiply scattered light is
recorded from the forehead of subjects during hyperventilation. Blood flow within the sampled tissue volume is
estimated by the mean decay rate of g(2) (τ) . Data measured from six subjects show that the pattern of the hemodynamic
response during 50 s hyperventilation is rather complicated: within the first 10 s, in three subjects an initial increase in
blood flow is observed; from 10 s to 20 s, the mean blood flow is smaller than its baseline value for all six subjects; for
the duration from 20 s to 30 s, the blood flow increases again. However, after 30 s the change is not consistent across
subjects. Further study on one of these subjects by using two receivers probing the blood flow in the cortex and in the
superficial layers simultaneously, reveals that during hyperventilation, the direction of change in blood flow within the
scalp is opposite to the one in the brain. This helps to understand the complicated hemodynamic response observed in
our measurements.
Diffusion coefficients in the human sensorimotor and visual cortices were measured using diffusing-wave spectroscopy. Motor and visual activation leads to increases of the diffusion coefficients in the respective cortical areas over the values at rest.
We use near-infrared dynamic multiple scattering of light [diffusing-wave spectroscopy (DWS)] to detect the activation of the somato-motor cortex in 11 right-handed volunteers performing a finger opposition task separately with their right and left hands. Temporal autocorrelation functions g(1)(r,) of the scattered light field are measured during 100-s periods of motor task alternating with 100-s resting baseline periods. From an analysis of the experimental data with an analytical theory for g(1)(r,) from a three-layer geometry with optical and dynamical heterogeneity representing scalp, skull, and cortex, we obtain quantitative estimates of the diffusion coefficient in cortical regions. Consistent with earlier results, the measured cortical diffusion coefficient is found to be increased during the motor task, with a strong contralateral and a weaker ipsilateral increase consistent with the known brain hemispheric asymmetry for right-handed subjects. Our results support the interpretation of the increase of the cortical diffusion coefficient during finger opposition being due to the functional increase in cortical blood flow rate related to vasodilation.
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