Ultraviolet astronomy and planetary science is often the study of large, extended objects with little point-source spectrographs or 1D long-slit imaging spectrographs. This limitation is necessary for spectroscopy at nearly any wavelength – spectrographs produce an image of whatever is input into them in its component colors, with each color reflecting off of the grating at slightly different angles. If you have a two-dimensional object, then that two-dimensional shape will be replicated thousands of time in different colors in images that will overlap in what as known as “spectral confusion.” A one-dimensional object, however, will simply be a series of lines that will not overlap, allowing the scientist to see what colors the object is emitting.
For astronomy, where targets are usually fairly static, this limitation means that instruments must spend a large amount of time scanning objects to fully cover it, or simply observe a small region of the object and attempt to extrapolate the science from a limited set of data. For planetary science, especially of transient phenomena such as comets or eruptions from active Solar System bodies, this limitation means that the dynamic picture is often incomplete.
The Ultraviolet Micromirror Integral-field Spectrograph (UMIS) is a joint LASP, Ball Aerospace and Planetary Science Institute project to use MEMS micromirror devices to “dissect” a telescope focal plane and reformat it into one dimension, thereby allowing spectroscopy without spectral confusion. This is achieved with an array of small mirrors that can each be electro-mechanically oriented to reflect light at a different angle, and then a second array of similar mirrors that remove that angle to re-align the light beams into the new format. Thus a two-dimensional image can be reconstructed into a one-dimensional image and dispersed by a spectrograph without spectral confusion. The image can then be reconstructed to get the spatial information.
This has been done before with static mirror arrays (see INFUSE). In static imaging slicing designs the field-of-view and resolution of the instrument are fixed parameters that must be traded off against each other, as there is limited space on the detector to capture the signal. UMIS does it dynamically, enabling an instrument where only the optimal regions of a wide FOV are selected. This allows for medium or high angular resolution over a large FOV, provided not all portions of the sky are needed.
The UMIS testbed is currently under fabrication at CU-LASP, with the objective of demonstrating the proof-of-concept breadboard by 2022. This work is funded by the NASA PICASSO program. The primary CUSP team members involved at Prof. Brian Fleming, Dr. Dmitry Vorobiev, Dr. Jack Williams, Dr. Ambily Suresh, and CU Physics student Trent Rabe.