There is a large performance gap between conventional, electron-impact X-ray sources and synchrotron radiation sources. An Inverse Compton Scattering (ICS) source can bridge this gap by providing a narrow-band, high-flux and tunable Xray source that fits into a laboratory. It works by colliding a high-power laser beam with a relativistic electron beam, in which case the energy of the backscattered photons is in the X-ray (or gamma-ray) regime. Here we present a new conceptual design for an ICS source that is more than two orders of magnitude brighter than the Lyncean Compact Light Source (CLS) currently in user operation. Depending on configuration, this next generation CLS covers an X-ray energy range of about 30-90 keV, or 60-180 keV. It will provide X-ray flux of up to 4 x 1012 photons/s within a beam divergence of 4 mrad and a bandwidth of around 10%. This is well-suited for micro-CT imaging of millimeter-sized samples at micron resolution, with a flux density similar to some high-energy synchrotron beamlines. The beam properties of the new design are also compatible with narrower bandwidth, focused beam applications such as high-energy diffraction. We discuss the novel concepts applied to the design of this X-ray source as well as the resulting beam properties. We present application examples in the areas of imaging, diffraction, and radiotherapy where this system can approach or match the performance of synchrotron beamlines. This will allow transferring many research, industrial and medical applications from the synchrotron, where capacity and access are limited, to a local lab or clinic.
Spectralus presents its progress in development of miniature, highly efficient, and versatile
diode-pumped solid-state (DPSS) green laser source, based on a monolithic cavity microchip
laser platform. The use of periodically poled MgO-doped Lithium Niobate (PPMgOLN) as the
nonlinear frequency doubler together with gain material Nd3+:YVO4 allows obtaining a
significant increase in the overall efficiency of the green microchip laser in comparison with
other compact green laser source architectures with comparable output power. Originally, this
laser source was designed to be part of the miniature and efficient RGB light source for
microdisplay-based (LCOS, DLP or similar) mobile projector devices. Recently, we have
extended range of operations for our original laser platform. In particular, we demonstrate the
following: high peak power (>500mW), high average power (>200mW), broad temperature
range of operation (-30°C - 60°C), and low noise CW operation (<0.5% RMS).
We report on highly efficient diode-pumped solid-state (DPSS) green laser source based on a monolithic cavity
microchip laser platform. The use of periodically poled MgO-doped Lithium Niobate (PPMgOLN) as the nonlinear
frequency doubler together with gain material Nd3+:YVO4 allows obtaining a significant increase in the overall
efficiency of green microchip laser in comparison with other compact green laser source architectures with comparable
output power. We discuss our progress in miniaturization and efficient operation across a wide range of temperatures
and application-specific modulation conditions. In particular, we demonstrate 50mW-120mW average green output
power (30% duty cycle) with wall-plug efficiency over 13%. Efficient laser operation with duty cycle ranging from 10%
to 60% in a wide range of repetition rates is also demonstrated. The laser is designed to be a part of the miniature and
efficient RGB light source for microdisplay-based (LCOS, DLP or similar) mobile projector devices. While these
projection architectures typically require modulation rates from 60Hz to about 2000Hz depending on design, we
extended modulation speed up to 2MHz that can be of interest for other applications. A very efficient and small
microchip as well as alignment-free design allow us to package this laser source into the very small volume of only
0.23cm3 (bounding box). We present results of performance tests for this packaged laser and demonstrate that such a
miniature package can support laser operation with average power output of over 250mW.
Recent developments in compact projectors sparked interest in light sources for these applications. While RGB lasers
offer advantages, a viable green laser platform has been difficult to realize. In this work, we demonstrate a novel green
laser source, based on a monolithic cavity microchip laser platform. The use of highly efficient, periodically poled MgOdoped
Lithium Niobate (PPMgOLN) as the nonlinear frequency doubler allows obtaining a significant increase in the
overall efficiency of the green microchip laser. Specifically, we demonstrate 50-150mW green output with wall-plug
efficiency exceeding 10% in the temperature range over 40°C. We discuss a compact package for this laser source with
volume less than 0.4cm3.
Mode-locking of a pulsed picosecond Nd3+:YAG laser using a slow solid-state saturable absorber with microsecond recovery time (Cr4+:YAG) and a passive negative feedback element (GaAs) is reported.
We have combined Mie scattering theory and image theory to predict the forward scattering of light from spherical particles in a seeded fluid using high numerical aperture collection optics. Using this method, it is possible to determine all three components of a fluid's velocity by measuring the scattering from homogeneous spherical particles without moving the optics. The transverse velocity component is determined by following the centroid of the scattering pattern (with respect to time), while the component along the optical axis is determined by comparing the experimental data with numerical computations. We have verified our theoretical model and computer code by measuring the scattering from polystyrene particles illuminated with partially coherent, Koehler illumination in a transmitted light microscope. The three-dimensional scattering data is in quite good agreement with our model. To further verify our approach, we have measured the three- dimensional (parabolic) profile of a parallel flow of a low viscosity, seeded fluid in a straight channel (6 mm by 48 mm by 0.315 mm). The channel was placed on the stage of a conventional microscope equipped with a long working distance microscope objective, with the narrow dimension along the optical axis (OA). Instead of directly imaging the seed particles, the forward scattered light is recorded from the spherical, polystyrene seed particles (7 micrometer diameter).
We have combined the principles of phase-shifting interferometry (PSI) and laser-feedback interferometry
(LFI) to produce a new instrument that can measure both optical path length (OPL) changes and
discern sample reflectivity variations. In LFI, coherent feedback of the incident light either reflected directly
from a surface or reflected after transmission through a region of interest will modulate the output
intensity of the laser. LFI can yield a high signal-to-noise ratio over a broad range of sample reflectance.
By combining PSI and LFI, we have produced a robust instrument, based upon a HeNe laser, with high
dynamic range that can be used to measure either static (dc) or oscillatory changes along the optical path.
As with other forms of interferometry, large changes in OPL require phase unwrapping. Conversely,
small phase changes are limited by the fraction of a fringe that can be measured. We introduce the phase
shifts with an electro-optic modulator (EOM) and use either the Cane or Hariharan algorithms to determine
the phase and visibility.
We have determined the accuracy and precision of our technique by measuring both the bending of a
cantilevered piezoelectric bimorph and linear ramps to the EOM. Using PSI, sub-nanometer displacements
can be measured and, as with other forms of PSI, there is no sign ambiguity to the displacement
measurement. We have also analyzed the behavior ofthe interferometer for both low and high reflectivity
samples. Since the change in the laser's intensity is a non-linear function of the reflected amplitude, additional
measures are required before applying PSI methods to high reflectivity samples.
We describe in detail the mechanism of 20-fold pulse compression in a synchronously pumped optical parametric oscillator. Nonlinear compression of these soliton-like pulses arises from pump depletion by the leading front of the compressed pulse and is limited by the round-trip cavity losses.
We employ Forward Scattering Particle Image Velocimetry (FSPIV) to measure all three components of the velocity of a buoyant polystyrene particle in oil. Unlike conventional particle image velocimetry (PIV) techniques, FSPIV employs coherent or partially coherent back illumination and collects the forward scattered wavefront; additionally, our field-of-view is microscopic. Using FSPIV, it is possible to easily identify the particle's centroid and to simultaneously obtain the fluid velocity in different planes perpendicular to the viewing direction without changing the collection or imaging optics. We have trained a neural network to identify the scattering pattern as function of displacement along the optical axis (axial defocus) and determine the transverse velocity by tracking the centroid as function of time. We present preliminary results from Mie theory calculations which include the effect of the imaging system. To our knowledge, this is the first work of this kind; preliminary results are encouraging.
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