Ultra-precision Diamond Tooling Research Articles

Miniaturized broadband spectrometer based on a three-segment diffraction grating for spectral tissue sensing

Compact and broadband spectrometers are very useful in various application domains such as agriculture, food, health and security. In minimally-invasive image-guided procedures spectral tissue sensing helps for screening and diagnostic purposes aiming at discriminating between healthy and tumorous tissue at point-of-care locations and outpatient centers. We designed a compact spectrometer based on a three-segment diffraction grating which operates from 300 nm to 1700 nm. The first two segments of the grating cover spectral ranges from ultraviolet to visible and near infrared (UV, VIS/NIR), whereas the third segment covers the short-wave infrared (SWIR) region from 830 nm to 1700 nm. The spectrometer has a resolution of 6 nm in the UV-VIS/NIR ranges and 10 nm in the SWIR range. The smallest signal-to-noise ratio (SNR) of the spectrometer achieved in the VIS range is 650 and in the SWIR range 9300. Afterwards, the designed three-segment grating was fabricated in-house with ultra-precision diamond tooling followed by hot embossing and quantitatively characterized. The experimental results show that the three-segment grating improves the diffraction efficiency in the NIR-SWIR wavelength range by at least a factor of 2 compared to a Richardson grating which only operates from 300 nm to 1100 nm. This result paves the way towards a new approach for making compact and low-cost spectrometers which could be integrated with hand held devices such as tablets and smartphones.

Compact conical beam shaper and freeform segmented reflector for SERS analysis.

We present a Raman spectroscopy setup containing a conical beam shaper in combination with a freeform segmented reflector for surface enhanced Raman scattering (SERS) analysis. The freeform segmented reflector and the conical beam shaper are designed by numerical approaches and fabricated by means of ultra-precision diamond tooling. The segmented reflector has a numerical aperture of 0.984 and a working distance of 1mm for SERS measurements. We perform systematic simulations using non-sequential ray tracing to assess the detecting abilities of the designed SERS-based system. We implement a proof-of-concept setup and demonstrate the confocal behavior by measuring the SERS signal of 10µM rhodamine B solution. The experimental results agree well with the simulations concerning the misalignment tolerances of the beam shaper with respect to the segmented reflector and the misalignment tolerances of the collecting fiber. In addition, we conduct benchmark SERS measurements by using a 60× objective lens with a numerical aperture of 0.85. We find that the main Raman intensity of rhodamine B at 1502 cm-1 obtained by our segmented reflector working together with the conical beam shaper is approximately 30% higher compared to the commercial objective lens.

Mass-manufacturable polymer microfluidic device for dual fiber optical trapping

We present a microfluidic chip in Polymethyl methacrylate (PMMA) for optical trapping of particles in an 80µm wide microchannel using two counterpropagating single-mode beams. The trapping fibers are separated from the sample fluid by 70µm thick polymer walls. We calculate the optical forces that act on particles flowing in the microchannel using wave optics in combination with non-sequential ray-tracing and further mathematical processing. Our results are compared with a theoretical model and the Mie theory. We use a novel fabrication process that consists of a premilling step and ultraprecision diamond tooling for the manufacturing of the molds and double-sided hot embossing for replication, resulting in a robust microfluidic chip for optical trapping. In a proof-of-concept demonstration, we show the trapping capabilities of the hot embossed chip by trapping spherical beads with a diameter of 6µm, 8µm and 10µm and use the power spectrum analysis of the trapped particle displacements to characterize the trap strength.

Free-Form Optics Enhanced Confocal Raman Spectroscopy for Optofluidic Lab-on-Chips

We present an optofluidic lab-on-chip for confocal Raman spectroscopy, which can be used for the analysis of substances. The device strongly suppresses unwanted background signals because it enables confocal detection of Raman scattering thanks to a free-form reflector embedded in the optofluidic chip. We design the system using non-sequential ray-tracing combined with a mathematical code to simulate the Raman scattering behavior of the substance under test. We prototype the device in polymethyl methacrylateby means of ultraprecision diamond tooling. In a proof-of-concept demonstration, we first show the confocal behavior of our Raman lab-on-chip system by measuring the Raman spectrum of ethanol. In a next step, we compare Raman spectra measured in our lab-on-chip with spectra measured with a commercial Raman spectrometer. Finally, to calibrate the system we perform Raman measurements on urea solutions with different concentrations with our proposed experimental proof-of-concept setup. We achieved a detection limit that corresponds to the noise equivalent concentration of 20 mM.

Demonstration of a multichannel, multiresolution imaging system

In conventional multichannel imaging systems, all channels have similar imaging properties [field-of-view (FOV) and angular resolution]. In our approach, channels are designed to have different imaging properties which add multiresolution capability to the system. We have experimentally demonstrated, for the first time to our knowledge, a three-channel imaging system which simultaneously captures multiple images having different magnifications and FOVs on an image sensor. Each channel consists of four aspherical lens surfaces fabricated from four PMMA plates by ultraprecision diamond tooling and of a baffle made from a titanium (Ti) and aluminum (Al) based metal alloy. The integrated imaging system is able to record a FOV of 7.6° with the first channel and 73° with the third channel while having a magnification ratio of about 6 between them. The experimental and simulation results, specifically the FOV and magnification ratios, are comparable, and this paves a way for low-cost, compact imaging systems which can embed smart imaging functionalities.