Technique for diamond machining large ZnSe grisms for the Rapid Infrared/Imager Spectrograph (RIMAS)

The Rapid Infrared Imager/Spectrograph (RIMAS) is an instrument designed to observe gamma ray burst afterglows following initial detection by the SWIFT satellite. Operating in the near infrared between 0.9 and 2.4 μm, it has capabilities for both low resolution (R~25) and moderate resolution (R~4000) spectroscopy. Two zinc selenide (ZnSe) grisms provide dispersion in the moderate resolution mode: one covers the Y and J bands and the other covers the H and K. Each has a clear aperture of 44 mm. The YJ grism has a blaze angle of 49.9° with a 40 μm groove spacing. The HK grism is blazed at 43.1° with a 50 μm grooves spacing. Previous fabrication of ZnSe grisms on the Precision Engineering Research Lathe (PERL II) at LLNL has demonstrated the importance of surface preparation, tool and fixture design, tight thermal control, and backup power sources for the machine. The biggest challenges in machining the RIMAS grisms are the large grooved area, which indicates long machining time, and the relatively steep blaze angle, which means that the grism wavefront error is much more sensitive to lathe metrology errors. Mitigating techniques are described.

[1]  E. Ramirez-Ruiz,et al.  Gamma-Ray Bursts in the Swift Era , 2009, 0909.1531.

[2]  Paul J. Kuzmenko,et al.  High efficiency germanium immersion gratings , 2006, SPIE Astronomical Telescopes + Instrumentation.

[3]  Edward W. Dunham,et al.  Status and performance of the Discovery Channel Telescope during commissioning , 2012, Other Conferences.

[4]  Douglas B. Leviton,et al.  High accuracy, absolute, cryogenic refractive index measurements of infrared lens materials for JWST NIRCam using CHARMS , 2005, SPIE Optics + Photonics.

[5]  Alexander S. Kutyrev,et al.  The development and analysis of cryogenic optical systems for the rapid infrared imager/spectrometer , 2013, Optics & Photonics - Optical Engineering + Applications.

[6]  Jiwang Yan,et al.  Prediction of subsurface damage depth of ground brittle materials by surface profiling , 2007 .

[7]  Paul J. Kuzmenko,et al.  ZnSe immersion grating in the short NIR region , 2014, Astronomical Telescopes and Instrumentation.

[8]  Paul J. Kuzmenko,et al.  Progress in the fabrication of a prototype ZnSe immersion grating for the WINERED spectrograph , 2010, Astronomical Telescopes + Instrumentation.

[9]  Paul J. Kuzmenko,et al.  Fabrication and testing of diamond-machined gratings in ZnSe, GaP, and bismuth germanate for the near-infrared and visible , 2008, Astronomical Telescopes + Instrumentation.

[10]  Alexander S. Kutyrev,et al.  Cryogenic optical systems for the rapid infrared imager/spectrometer (RIMAS) , 2014, Astronomical Telescopes and Instrumentation.