Soft X-ray Polarimeter Concepts

A Narrow-band Approach

The PLEXAS design was proposed to NASA as a small explorer in 1998. A paper on this approach was presented at the 2002 SPIE meeting.

A Broad-band Approach

The basic concept was outlined in Paper 1 (pdf), presented at the SPIE meeting in 2007. This approach could be used to measure X-ray polarization across the band from 0.2 to 0.8 keV.

Paper 2 (pdf) was presented at the SPIE meeting in 2008, this paper was presented at the Rome X-ray Polarimetry meeting held in April, 2009, and Paper 3 (pdf) was presented at the SPIE meeting in 2010. This approach could be implemented as a small mission or used on a large X-ray astronomy mission such as AXSIO (pdf).

Examples of targets for both instruments:

Recent Work:

A laboratory for demonstrating critical components of this design is also described in Paper 3. A small scale version of the laboratory work was started in the summer of 2009 with MIT Kavli internal funding and now has NASA APRA funding. See this pdf for a presentation at the 2013 SPIE meeting in San Diego and see this pdf for the submitted paper with more details.


A successful polarization test, as published in 2013. The polarization source is 100% polarized and its orientation was rotated through 150 degrees to demonstrate that the system can produce, rotate, and measure polarized X-rays.

More recently, we have entered Phase III, where we are using laterally graded multilayer coated mirrors (LGMLs). We show results in this paper, published in the proceedings of the 2014 SPIE meeting (volume 9144), held in Montreal, Canada. New LGMLs were obtained from Reflective X-ray Optics (RXO) and measured at the (Advanced Light Source in Berkeley. Results were published in 2015. A sounding rocket proposal has been submitted to NASA. Some of the engineering renderings and raytrace results are shown in a presentation to the eXTP Mission Design Coordination Meeting (held 3/21-23/17 in Beijing, PRC) about providing a similar instrument for eXTP.

Recent Pictures:


The MIT X-ray Polarimetry Beamline. The polarizing source is at left, the grating chamber is in the center of the beamline and the detector chamber is at right. The entire beamline is about 19 m long.

The polarizing source. The (unpolarized) X-ray source is the chamber at right that is horizontal and parallel to the beamline. A laterally graded multilayer coated mirror is installed in a chamber at the intersection of the source output and the beamline. The mirror is mounted at the end of a vertical shaft, rotatable by the manipulator that is pointed slightly to the left of the camera. A linear drive (at right) compresses the bellows, moving the mirror's position in the chamber to select different multilayer coating periods for optimal reflectivity and polarizing the reflected X-rays.

The detector chamber. The X-ray sensitive CCD is at the left end of the system, to which is attached a liquid nitrogen feed line for cooling to -75deg C. The detector electronics are in the foreground on a cart with four power supplies. The detector control and analysis computer is on the table.

For more information, see Herman Marshall, or send e-mail to hermanm -at- space.mit.edu.

Updated: March 22, 2017