As the tilt increases, the anamorphic factor increases to about 1.9.
Echelle grating zemax file movie#
The movie begins in the Littrow configuration ( and ) and each frame of the movie increases the amount of grating tilt. The grating operates at a wavelength of 550 nm, with a ruling density of 280 line per millimeter operating in fifth order. The grating is either tilted or rotated (which varies with each frame of the movie), and the outgoing beam is fed into a perfect (paraxial) camera. In the spectrograph, a single circular collimated beam illuminates a grating. The optical model shown in these videos represents a simplified spectrograph. As the web page loads, the videos should play in sync (if not, try reloading). To illustrate the point, I’ve used zemax raytraces to create a number of videos that demonstrate the phenomenon and effect of anamorphism. In short, the slit image shrunk in the dispersion direction. With an anamorphic factor of 1.3, the plate scale is (Telescope Diameter) (Camera f/#) / (206265 ) or 75.0 µm /arcsecond. For instance, the 10 m Keck telescope with an f/2.0 camera has a plate scale of 97.0 µm / arcsecond. Recall that the plate scale of a spectrograph is the (Telescope Diameter) ⨉ (Camera f/#) / 206265. To the observer, the main consequence of anamorphic magnification is a change in the plate scale of the spectrograph in the dispersion direction.
Reflective grating spectrographs often have anamorphic factors in the 1.3 to 1.5 range (see also Schweizer (1979)). If one uses grisms or volume-phase holographic gratings, the anamorphic factor again is unity. Note that if the spectrograph is operated in Littrow (e.g., high-resolution echelon spectrographs) then and is unity. The grating produces an elliptical shaped pupil with a minor axis diameter equal to the spectrograph beam size ø, and the major axis diameter is the anamorphic factor times the beam size ( ). It is straightforward to compute the anamorphic factor as Basic TheoryĬlassical anamorphism arises when a grating is tilted around its rulings. I conclude by describing some key differences between tilt and anamorphism.
In this post I show “classical” anamorphism that arises from tilting a grating around its rulings, as well as rotation or anamorphism that arises from rotating a grating (see figures below for axis). Anamorphism arises when a grating is used off of the Littrow condition. Specific to spectrographs, anamorphic magnification is a scalar value defined as the ratio of diameters of the major to minor axis in the pupil. Anamorphism is a general property of geometric optical systems with. The anamorphic magnification of ruled-grating spectrographs is a property that must be understood and accounted for when designing ground-based spectrographs. These could be fed by a small network of 1-m telescopes to play an important role in the long-term future of spectroscopic classification of transient events. Our long-term vision is to build not just one R2S2I but multiple. will revolution time-domain astrophysics with alerts issued on tens-of-seconds timescales. In just a few years a whole slew of facilities including LSST, ASAS-SN, ZTF, TESS, etc. The spectrograph operates at a spectral resolution of 1,000: allowing to to both classify and perform some of the initial science.Īs a result R2S2I will be able to participate in this golden age of rapid-response astronomy. By using a slicer we’ll be able to classify thousands of transients per year down to r~20 on the 40-inch Henrietta Swope Telescope at Las Campanas Observatory.
Echelle grating zemax file plus#
R2S2I uses a wide-field and rapid-readout imager plus a slicer-based integral field unit. The instrument has been designed as a followup based on lessons learned from both SED Machine (on the Palomar 60 inch) and FLOYDS (on the Las Cumbres Observatory 2 m). The goal of R2S2I is to be the instrument of choice for rapid followup of transient events. We lovingly call it R2S2I or the “Rapid Response Swope Spectrograph and Imager”. Recently, with the help of postdoc Decker French we have been looking into the design of a new rapid-response spectrograph and imager.