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March 12, 2022

While successful, implementation of collimated beam projector to date has two issues: 1) dynamic range mismatch between monitor diode (wants nA of current) and astronomical instrument (100,000 electrons per pixel max), and 2) not directly monitoring beam at exit pupil, due to size mismatch. 

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At 808 nm: 

If angle of incidence is 10 degrees, reflected beam rotates by 20 degrees. If beam of diameter D rotates by theta, distance it must travel to not have incident and reflected overlap obeys tan(theta)=D/L so L/D=1/tan(theta)

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notional system diagram: 

RACBP Spring 2024 Parts List:

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We note the reflective designs in this paper which document a 4-element system that adequately* preserves the initial polarization / phase of light.

Status updates: 

An initial version of the RACBP was constructed in the benchtop lab setup on Feb. 22.

Initial testing with a 532nm laser unfortunately showed strong and tightly spatially located double-bounce propagation through the system, indicating that the 30-arcmin wedge on the wedge windows purchase would be insufficient for canceling double-bounce issues. 

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Consequently, plano-convex lenses of the fastest f-ratio were ordered and installed the following week as replacements to the wedge windows; initial observation reveal that this modification  appears to successfully cancel out double bounces, representing a step closer to taking controlled flux measurements through the system at this proof-of-concept stage. 

Current status of the project is temporarily described in this document.

Reference:

(Galvez, E. (2001). Achromatic polarization-preserving beam displacer. Optics Letters, 26(13), 971–973. https://doi.org/10.1364/OL.26.000971)

References

Large optical wedge vendor, example: https://www.precisionoptical.com/precision-optics/optical-flats/unmounted-reference-flat/

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polarization-preserving configuration with 4 reflections ol-26-13-971.pdf; (Galvez, E. (2001). Achromatic polarization-preserving beam displacer. Optics Letters, 26(13), 971–973. https://doi.org/10.1364/OL.26.000971)

We note the reflective designs in this paper which document a 4-element system that adequately* preserves the initial polarization / phase of light.