Dichroic Beamsplitters

M.Lampton

UCB SSL

Dec 2003

M.Lampton Dec 2003 2

Why a dichroic beamsplitter?

• Separating the VIS and NIR sensors could double our observing efficiency!– with our present FIDO, a NIR photon arriving at a VIS detector is lost,

ditto the reverse

• but... would need two focal planes contrary to our FIDO decision

• If we had twice the observing efficiency, perhaps we could....– double the SN harvest?

– or use a smaller telescope and payload?

– or use fewer detectors?

– etc

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Dichroics are offered by many vendors…

• Edmund Optics– http://www.edmundoptics.com– 1-800-363-1992

• OCLI– http://www.ocli.com– 1-707-525-6957

• Barr Associates– http://www.barrassociates.com– 1-978-692-7513

• Omega Optical– http://www.omegafilters.com– 1-802-254-2690

• Melles Griot– http://www.mellesgriot.com– 1-800-835-2626

• Spectrogon US– http://www.spectrogon.com– 1-973-331-1191

• Spectro-Film Inc– www.spectrofilm.com– 1-978-670-7192

• Optical Coating Technologies– www.coatingoptics.com– 1-413-564-0700

• North American Coating Labs– www.nacl.com– 1-866-216-6225

• Opticorp Inc– http://www.opticorp.com– 1-978-250-8115

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Technology“hot mirror” reflects IR, transmits VIS

“cold mirror” reflects VIS, transmits NIR

• Wideband substrate: borofloat, BK7, or silica

• Multilayer dielectric layers on front side

• Broadband antireflection coating back side

• Typical application is removing heat from an illuminator (projector, microscope…)

• Typical application subjects dichroic to sudden heat, many thermal cycles

• Typical application does not demand high precision bandpass nor image quality

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Melles Griot

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Edmund cold mirrors

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Edmund extended hot mirrors“extended” means goes to 1.7um

Transmission

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OCLI cold mirrors

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OptiCorp Inc

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Conclusions

• Plenty of vendors!

• Most of the commercial offerings are for simple “heat dump” applications, non imaging and not very critical of exact bandpass shape or stability

• Tough! Withstand enormous thermal abuse.

• Issues of sub arcsecond image quality and long term stability would need to be explored with one or more prospective vendors

• Vendors are happy to bid on our requirements for stability, flatness, voids/flaws, stray, efficiency & curve shape, environmental, you-name-it.