There are a variety of dichroic beam splitters available from various vendors. The dichroic beam splitter that we will be modeling is based on one that can be purchased from CVI Laser, LLC. The dichroic beam splitters available for purchase from CVI can be assigned any one of a number of dichroic coatings that are available.

The beam splitter that we will be modeling is a Short Wave Pass (SWP). This particular type of beam splitter is characterized by high transmission (i.e. low reflectivity) at short wavelengths along with low transmission (i.e. high reflectivity) at longer wavelengths. Here is a transmission vs. wavelength curve for a typical SWP dichroic coating:

Full details on CVI Laser’s SWP dichroic beam splitters can be found on this webpage:

            http://www.cvilaser.com/Catalog/Pages/Template2.aspx?pcid=87&filter=0

Dichroic coatings are characterized by a pass band (wavelength region of high transmission/low reflectivity), a stop band (wavelength region of low transmission/high reflectivity) and a transition region (the wavelength region between these two bands):

For more information on how dichroic beam splitters work, please see the following document:

            http://www.cvilaser.com/Common/PDFs/Dichroic_Beamsplitters_Discussion.pdf

For the purposes of modeling simplicity, we are going to model a somewhat idealistic version of a typical SWP dichroic beam splitter from CVI. Our modeling assumptions will include:

• We do not have access to the full coating prescription data
• The dichroic coating with be polarization insensitive
• The transmission in the pass band will be 100%
• The reflection in the stop band will be 100%
• We will not do any modeling of the transition region

It is important to note that these idealistic assumptions are certainly not required in ZEMAX. As you will see, ZEMAX’ coating modeling capabilities allow for very realistic coating modeling. We are making the above assumptions simply to simplify the work that we will have to do in this case.

The SWP dichroic beam splitter that we will model will have the following properties:

• Substrate:  N-BK7
• Clear Aperture:  1”
• Thickness:  0.25”
• Dichroic coating on front surface of substrate
• Pass wavelength:  0.400 mm
• Stop wavelength:  0.525 mm
• The rear and edge surfaces of the substrate will be coated with an ideal 1% reflection/99% transmission anti-reflection (AR) coating