Quantum Gravimeters
To precisely measure the value of gravitational acceleration, precisely till the 8th decimal place, a quantum sensor needs to remove all sources of noise from the system. Slight changes in alignment, temperature, humidity or vibration can introduce massive errors. This can corrupt our data that predicts the exact geolocation of mineral reserves. Along with stability, a gravimeter also requires hundreds of precisely engineered opto and electro-mechanical tools to cool down atoms below 10 micro Kelvin.
I design these mechanical systems for laser-optics and electronics. I have successfully fabricated vacuum chambers, laser alignment tools and environment control systems to stabilize temperature, vibrations and stray magnetic fields. Key components that I have designed are:
- Pyramid retroreflector
- 2 DOF flexure periscope
- Portable atom interferometer
- Vibration isolation system
- Liquid cooled magnetic coils
Optics Breadboard
This breadboard contains the main laser source and amplifier along with a series of lenses, mirrors and beam splitting cubes. 780nm laser beam is guided and tuned through this assembly using acoustic and electronic modulators
I design opto-mechanical jigs, mounts and fixtures for these components. Designs and material selection is done after thermal and vibration simulations. My work includes
- IP 67 casing for tapered amplifier.
- Quarter wave-plate rotation mount
- Beam blockers and beam dumps
- Kinematic mounts for mirrors
- Polarised beam splitter cube enclosure
- Temperature controllers for laser source
Fiber periscope
To save space and make the optics compact, beam heights are alternated between 16mm and 40mm. For correct laser alignment, two degrees of freedom is required on both flanges. While allowing micro angular movements through the actuators, the periscope should remain thermally stable. In the fabrication and testing process 7 different materials were tested and simulations were done on DetasFlex
Construcction
- Titanium unibody
- 100 TPI ( threads per inch ) kozzak actuators
- Sapphire discs at bearing end
- 2 way butterfly hinge
- Milling on 5-axis CNC
- Orthogonal cuts using wire EDM
Miniaturization
Atom interferometers are generally lab sized equipment owing to its complexity and stability requirements. In the past 2 years I have re-engineered more than 50 critical components to bring down the size of the apparatus to 20cm x 20cm x 30cm. This could potentially be the world's smallest gravimeter. The image on the right is version 1 (300+ Kg). The image on the left is version 2 (23 Kg)
Key elements of design
- Modular vacuum chamber
- Independent atom trapping unit
- Integrated laser source
- Compatible with gyro stabilisation platform
- Lightweight magnesium alloy enclosure
Meet the team
Atomionics was started in 2018 by researchers from the Center for Quantum Technology, NUS. The video talks about working principles, applications and the diverse culture of atomionics. I am the oldest employee now. I feels great to see the team grow bigger in such a short time
CF 50 vacuum flange
Our vacuum chambers operate at 1nTorr pressure. Flanges that are used to seal these chambers have a meticulously designed knife edge that is pushed against an annealed copper gasket. Due to degassing problems only a handful of heat treated alloys can be used for making UHV flanges. This custom design had flange connectors on both sides, making the fabrication even more complicated. Before assembly all UHV components are polished, baked and washed in an ultrasonic bath to remove adsorbed impurities from the surface.
Pyramid retroreflector
To trap and cool down atoms inside a magnetic field, lasers need to bombard from all 6 directions. Generally 6 independent laser beams are used to create the atom cloud. I used a pyramid mirror and embedded it inside the vacuum chamber. This allows us to use a single laser collimator instead of 6 to save power and reduce complexity. Dielectric reflective coating was used on sapphire glass and vacuum compatible glue was used to join inclined mirrors together
Environmental controls
Stabilization systems which I designed/ worked on includes
- Negative stiffness vibration isolation
- Active vibration dampening using voice coils
- Liquid cooled and hermetically sealed electronics set-up
- Tilt alignment platform for high payload capacity
- 3 layered magnetic shielding using hydrogen annealed Fe-Ni alloy.
Atom cloud monitoring
Worked on cloud image processing analysis that reveals these following data points:
- Size of the cloud and the number of atoms inside it. Generally it is around 100 Million Rb atoms
- Temperature of the atoms. Range: 2-10 micro Kelvin
- Expansion rate and effect of gravity
- Distribution of atoms in 3D space
- Falling trajectory
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