Development of a high efficiency dichroic beamsplitter or the entire opticalNUV band

We propose to design, develop, produce and characterize, in tandem with the JPL-ASU partnership and our industry partner Materion Barr Precision Optics, a prototype optical-NUV dichroic element that delivers performance specifications we have identified as being central and critical to the success of the optical design for an existing Explorer-based mission concept, Orion. Ideally, we need a dichroic element that has a sharp transition between reflectance and transmittance at an intermediate wavelength (around 500nm), and has a smooth reflection/transmission curve for the blue/red (Figure 1). In reality, there are fundamental limits to the sharpness we can achieve in the transition, and the coatings used to reflect or transmit the photons will introduce rippling, peaks and troughs in the response that can and will intimately affect the spectral performance of the element (Figure 2). ASU, over the past 5-6 years, has been working in partnership with JPL on UV/optical space mission concepts that have at their heart large focal plane arrays to perform widefield imaging science at the diffraction limit afforded in space. We are currently working on an Explorer-class mission called Orion, which is a 1.1m UV/optical widefield imaging telescope intended for L2 orbit, but also being specified for LEO because of NASA-imposed launch vehicle restrictions. In this partnership, the optical design and 2 science program are being overseen by ASU, with JPL designing and building the twin-focal-plane camera, and integrating it with the telescope assembly (being provided by Goodrich). The detectors in this camera are CCD hybrids being developed using techniques and processes coming out of Dr. Shouleh Nikzads group at JPL. We are targeting proposing this mission as a mature, competitive, risk-mitigated solution as a MIDEX (MID-sized EXplorer) mission in the near future, once NASA SMD formulates its response to the recommendations of the recently-released NRC Decadal Survey on Astronomy and Astrophysics concerning the Explorer program (a factor of 2.5 increase in funding to Explorers over current levels and 2 MIDEX opportunities funded at the level of a $300M cost cap for each mission). A vital key to the Orion mission is maximizing the observing efficiency a primary piece of which is provided by employing a dichroic element in the optical path that sends all the blue light to one (blue-optimized) focal plane, and all the red light to a second (red-optimized) focal plane. This means no photons are thrown away and gives us an immediate factor of 2 increase in efficiency over a standard telescope+camera design. There are other parts of the design that provide additional increases (orbit, detector DQE, field of view) - the final tally is that our design will be as much as 100x more efficient than HST has been for this kind of science, and at least an order of magnitude better in discovery efficiency - the putative A-omega parameter - for location, characterization and analysis of small objects - either protostellar and protoplanetary systems in nearby massive stellar environments or Ly-alpha emitters at cosmological distances that are contributing to the problem of reionization of the early Universe. All that said, the dichroic is identified in our studies as being one of the central pieces of technology. No dichroics of the kind we're envisioning have been built or flown - and so it is our contention that development of this piece of technology is a vital strategic component if proposals to fly something like this are to be successful. Based on our most recent work for the Explorer concept, particular specifications have been identified for the dichroic element (included below in section 8). It is a component of this kind that we need to research, test and characterize on the bench as part of this SURP proposal. The SURP budget is small, but we believe the potential impact of this one component to our mission development, as well as that of other missions, makes this a good and smart investment on the part of JPL.