Tips on generating entangled photon pair with SPDC entanglement source

[PokemanDude]

TL;DR Summary

My lab is trying to produce entangled photons with an SPDC entanglement source, but we're having trouble aligning the setup to produce entangled photons. What are some alignment tips for this equipment?

Hello! In my summer lab, me and my labmates are trying to generate entangled photon pairs using a spontaneous parametric down-conversion (SPDC) entanglement source with BBO crystals. We're using a 405 nm diode laser from Matchbox with model number 405L-21A. Our setup is as follows: we shine the laser through the SPDC entanglement source, and it is supposed to produce a pair of entangled photons (one is 847 nm and the other is 776 nm) and send them into one end of a fiber optic. The other end directs the entangled photons into a 50/50 beamsplitter. On one output side of the beamsplitter, we placed a filter that lets through 780 nm light and then a photon detector, and on the other output side, we placed a filter that lets through 850 nm light and then a photon detector. To detect entanglement, we are looking to see coincidences in the two detectors.
We're having trouble producing entangled photons, and we suspect that the laser, entanglement source, and fiber optic aren't aligned properly. What are some tips for aligning these?

 

[Xuedong He]

Hello PokemanDude,

Questions,

1. Do you see some lasers generated by the parametric process at signal wavelength and idle wavelength? If you do see some lasers, it means the alignment process should be OK.
2. If you do see some lasers generated by parametric process, can you test the wavelengths and what are the results? If one of them is longer than 810 nm and another one is shorter than 810 nm, it means you do see the signal and the idle wave, meaning your alignment should be very close to what is being expected.

Recommendation,

If you do see the signal and idle wavelength, the next step should be doing some fine alignment to increase the efficiency and adjust the wavelength.

Regards,

Xuedong He

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