Rapid identification and the quantitative analysis of crystalline content and the degree of crystallinity is important in pharmaceuticals and polymer manufacturing. Crystallinity affects the bioavailability of pharmaceutical molecules and there is a strong correlation between the performance of polymers and their degree of crystallinity. Low frequency/THz-Raman spectroscopy has enabled determination of crystalline content in materials as a complementary method to X-ray powder diffraction. By incorporating motion stages and microplates, we have extended the applicability of THz-Raman technology to high-throughput screening applications. We describe here a complete THz-Raman microplate reader, with integrated laser, optics, spectrograph and software that are necessary for detecting low-frequency Raman signals.
In powder materials scattering is also affected by particle size and the presence of cavities, which lead to a lack of precision and repeatability in Raman intensity measurements. We address this problem by spatial averaging using specific stage motion patterns. This design facilitates rapid and precise measurement of low-frequency vibrational modes, differentiation of polymorphs and other structural characteristics for applications in pharmaceuticals, nano- and bio-materials and for the characterization of industrial polymers where XRPD is commonly used.
We report on the unique highly-configurable wavelength tuning and switching properties of a tunable external cavity
laser based on multiplexed volume holographic gratings (VHGs) and a micromirror device. The ultra-compact laser has
a 3 THz bandwidth and exhibits single mode operation in either single or multiple wavelengths with narrow linewidth
(<7.5 MHz), and a switching rate of 0.66 kHz per wavelength. A prototype laser exhibited 40 mW of output power for
wavelengths from 776 - 783 nm. The unique discrete-wavelength-switching features and low power consumption of this
laser make it well suited as a source for continuous-wave (cw) terahertz signal generation in portable photomixing
systems.
We have developed a fast multi-wavelengths switching laser platform. The tuning mechanism is based on a micro-mirror
array DLP chip from a commercial pico-projector forming the end mirror of an external cavity laser diode. We report
progress on a working prototype of a single frequency laser with a wavelength that is switchable between any five
wavelengths spanning 765 nm to 783 nm. Switching time between any two wavelengths is equal to the switching time of
the DLP micro-mirrors (milliseconds). We show that there is a clear path to realizing a tunable laser with over 50
discrete wavelengths. In addition to the fast switching time between any wavelengths, this laser has a compact form
factor (<1cm2) and the design is applicable to a broad spectral range spanning 400 nm to 3,000 nm.
We have developed a self-aligned external cavity laser with a non-dispersive volume holographic grating (VHG) as the
output coupler. The resulting external cavity is tunable by rotating the VHG. We have demonstrated tunable single mode
longitudinal operation at 405 nm and 785 nm wavelength. The passive alignment of the novel tunable laser is the main
driver for achieving low cost manufacturing. The axial symmetry enables the use of axially symmetric components such
as TO-can laser packages, lenses and VHGs which further reduces the cost of manufacturing and the laser footprint.
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