ASAHI SPECTRA天文二向色分束器Dichroic beam splitters

Dichroic beam splitters are getting more important for state-of-the-art spectro-graphs such as Dark Energy Spectroscopic

Instrument (DESI)， Prime Focus Spectrograph (PFS)， or multi-channel CCD cameras to take images in different colours simultaneously.

Dichroic beam splitters split the incident beam to two directions， therefore give the influence to the performance of at least

two or more cameras in terms of wavefront error， throughput， and available wavelength range.

ASAHI SPECTRA天文二向色分束器

Essential requirements for astronomical dichroic beam splitters are as follows.

• High reflection in (broad) band

• High transmission in (broad) band

  Both contribute the high overall throughput of the instrument.

• Sharp transition from reflection to transmission

  It contributes to minimize unavailable wavelength range.

  Key technique is to reduce the separation of p and s-polarization

  at specified angle of incidence.

• Minimized reflected wavefront error *after coating*

• Minimized transmitted wavefront error *after coating*

  Both contribute the image quality of the instrument.

There are few vendors in the world that can achieve all the requirements， a~e at the same time.

Asahi is one of potential vendors to provide such dichroic beam splitters with these performances.

We were successful in the fabrication of 390 mm x 365 mm， largest ever astronomical dichroic beam splitter for PFS in 2015.

The dichroic met all the hard specifications required by PFS project.

ASAHI SPECTRA天文二向色分束器曲线