In SPDC source often you need to separate single photons from laser pump. I would like to know what is the most efficient way when they are collinear. Dychroic Mirrors? Prims? both?
Well, it depends on the wavelength of the pump and signal. For the pump at 1064nm or 532nm, the dichroic mirror works well since the reflectivity of coatings at those wavelength can be as high as 99%. Then you can use a band-pass filter to remove the residual pump. In this way, the signal is in the same direction of the pump so that you can place your detector easily. Prism at Brewster angle can eliminate the interference completely and it also minimize the loss of the signal since you can have the signal photon p-polarized, however, the alignment can be a little bit hard if the signal is very weak. The direction of the beam is changed after the prism.
How about a Glan-Thomson? You don´t loose alignment, in principle. I guess you can choose the polarization to be the correct one to send the wavelength not in use to a beam-dump. Just a thought...
Thank you both for your suggestion and explanation. But what if we want to filter them in fibre? Without going into free-space. For example if we have combined in a wave-guide both single photons at 808 nm and a laser at 980 nm that can be also few uW , photons and laser have perpendicular polarization (lets say laser p polarised and photons s polarised). In this condition what is the most efficient?
I saw WDM for this purpose but they have like 30 dB separation and 1.2 dB of losses. The losses appear to be too much to me.
What do you think?
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