Precise alignment of laser beams used in heterodyne interferometry is vital and necessary to the precision, accuracy, and quality of the measurement, but off the shelf-based breadboard setups have a large physical footprint and many components that can introduce unwanted noise. Our lab creates optomechanical accelerometer devices including a fused silica resonator with a 5Hz natural frequency and uses a heterodyne displacement interferometer to readout the position of the test mass, which can then be used to determine the acceleration of the device. A novel compact fiber injector system design is presented here that reduces the footprint of the fiber collimator input of the heterodyne interferometer by an order of magnitude from a breadboard setup, down to 24 x 16 x 19 mm. This new injector system integrates both fibers of different frequencies directly onto the mount with the resonator, increasing stability and reducing entry points for vibrational noise while minimizing the optical path length difference between beams. Each beam can then be independently tilted and de-centered to maximize the fringe visibility at the output of the interferometer, using spring-loaded adjustment screws and secured in place with locking screws. An accelerometer using these injectors measured a displacement of 10-9 m/√Hz at 10-2 Hz in air with the test mass anchored, nearly identical to the previous breadboard setup while being much more compact and portable. I will present the design, integration onto an accelerometer, and the initial acceleration noise measurements taken using these fiber injector systems.
Accelerometers are key sensors in many fields and applications such as precision metrology, gravimetry measurements, gravitational wave observatories, and navigation where position and attitude need to be determined accurately. A combination of six accelerometers provides all the necessary information to estimate position and orientation of a rigid body and thus serves as an inertial navigation system for autonomous navigation. Fusedsilica based mechanical resonators paired with laser interferometric read-outs enable compact high-accuracy accelerometers. In this talk, we will present a wide-band accelerometer based on a double resonator with two test masses of different sizes in a single frame. One of the resonators has a resonance frequency of about 50 Hz, while the other is optimized for lower frequencies and has a nominal frequency of about 10 Hz. The combination of the two resonators allows for excellent long-term precision while maintaining good measurement bandwidth. We will show the experimental characterization in air and in vacuum of the double-resonator using a heterodyne laser interferometer and a fiber interferometer and its expected performance as an inertial sensor.
In addition to achieving a desired freeform profile, ensuring a superb micro-roughness finish is a key factor for successful freeform optics manufacturing. We present a pseudorandom orbiting stroke-based postprocessing technique that maintains freeform optic forms, while improving small-scale surface quality. The full-aperture tool can avoid subaperture effects, and the small stroke pseudorandom tool path guarantees the match of freeform profiles while preventing the directionality of the final surface profiles. Three independent experimental studies are designed, conducted, and presented for a wide range of optics, including magnetorheological finishing-polished BK7 glass, single-point diamond turned (SPDT) poly(methyl methacrylate), and SPDT Al6061 optics. The comparison of direct measured maps on the initial and final smoothed optics verifies the form maintenance capability of the freeform optics postprocessing technology. Surface roughness measurement highlights improvements in local surface roughness and periodic toolmark errors left by the previous polishing method.
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