Compact atomic magnetometer (AM) has potential applications in biomedical devices to measure magnetic signals from human organs, e.g. magnetocardiography and magnetoencephalography. Reducing the size of Helmholtz coils is an essential step for a design of compact AM, which also leads to lower cost in manufacturing processes. However, the homogeneity and magnitude of the magnetic fields and the size of a rubidium vapor cell must be considered for the decrease of the coil size. Here, we report a design of compact AM with square Helmholtz coils of 24×24×24 cm3 housing a rubidium vapor cell of 7.5 cm in length. The coils were calculated to induce a constant magnetic field of 0.5 gauss covering the length of 10 cm along the axis of symmetry of the coils. The field gradient was measured to be less than 4% of the magnitude over the distance of 6 cm. For zero-field condition, the field gradient was no more than 1 mgauss in all axes. Further developments of square Helmholtz coils for improving the field gradients are still needed before implementing in the compact AM.
We developed an economical assembly for a silicon photonics resonator device including a device mount and lensed fiber holders for input and output fibers. The parts are fabricated by 3D printing technology using resin with digital light processing (DLP) technique and cured with UV light (405nm). The lensed fibers are aligned to the device waveguides using 6-axis aligner platform and their holders are affixed to the device mount by UV glue. Our in-house assembly module is able to firmly affix the fiber holders to the device mount and align the input and output lens fibers to the device spot size converter (SSC) of dimension 3.4 × 3.5 μm2. After alignment completion, the assembly can be detached from the aligner stage to be used in un-stabilized benchtop measurement system. The benchtop measurement system for the silicon photonic sensor device consists of a tunable laser, a polarizer, an optical power meter, and a container housing the device assembly, peristalsis pump and control circuits that was developed inhouse for microfluidics control having flow rate in the level of nanoliter/minute. In addition, a software has been developed for the measurement of the device resonant wavelength and wavelength shift due to sensor activity. We have demonstrated that the silicon photonics resonator that has been mounted on our assembly in the above measurement system showed acceptable performance by comparing the results with those obtained by mounting the device on stabilized fiber alignment platform. Thus, the 3D printed assembly may be used for silicon photonics device mount in early portable sensor prototype development.
We explore the possibility of using transition energies of a doubly excited helium atom to describe the absorption lines of interstellar medium. We follow the method of approximated separation of variables in hypersperical coordinate in solving the energy levels of doubly excited helium. Although the results do not exactly match with the absorption spectrum of the diffuse interstellar bands, they show some correlation. We have also shown that the distribution of the difference between observed spectrum and the calculated result can be fit by normal distribution with the mean value close to zero. Furthermore, we argued that the distribution obtained from randomly generated lines are significantly different from the calculated result.
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