The optics subassembly conditions the light from the laser to make it suitable for probing the atoms. The main functions the optics sub-assembly performs are: attenuation of the light power to an appropriate level, collimation of the laser beam, and rotation of the polarization from linear to circular. The attenuation (by a factor of 50 to a power of 12 mW) is accomplished by use of pieces of optically dense glass. Collimation is accomplished by placed a commercially available microrefractive lens fabricated by inkjet deposition of optical epoxy. The lens is placed directly on the first ND filter, which is mounted on two glass legs to prevent the filter from coming into contact with the laser. A silicon spacer unit surrounds the lens and allows the other components, a thin (70 mm) piece of quartz and one additional attenuator to be mounted above. All components are bonded with high-temperature optical epoxy. The beam that comes out of the optics package has a diameter of about 250 mm.

References:

S. Knappe, L. Liew, V. Shah, P. Schwindt, J. Moreland, L. Hollberg and J. Kitching, "A microfabricated atomic clock," Appl. Phys. Lett., 85, 1460, 2004.

P. Schwindt et al., “Chip-scale atomic magnetometer with improved sensitivity by use of the Mx technique”, Appl. Phys. Lett. 90, 081102 (2007)