First Light spectrum obtained with new spectrograph.

Hi Michael,

I remember awhile back your interest when I spoke to you about exploring a new concept of imaging the Sun by obtaining multi-line observations and two dimensional spectroscopy, which can reveal the dynamic behaviour at different locations and wavelengths. By obtaining 2D spectral images with spacial info plus wavelength you can end up with 3D Sun at multiple wavelengths by designing a solar imaging spectrograph.

In order to answer your questions there are so many other aspects that are integral within this type of design

The Solar imaging spectrograph uses a heliostat type configuration. It has been designed to observe solar spectra in the range from 3000 to 10,000 A with a spectral resolution 0.2 A/mm. The system is composed of a 35cm diameter heliostat with a 20 cm achromat lens of f/16 (3.3m focal length), spectrographic system has a 400 groove/mm grating, and a 1k x 1k CCD detector.

The system consists of four elements, a heliostat, optical system, a CCD camera and software. The ray from the heliostat goes through a 20 cm achromat via the cut off filter (CF). However, the cut off filter only accepts the radiation covering from 3500A to 7000A. It can prohibit the optical system from heating up by cutting off the infrared and ultraviolet rays.

The development of the system will be able to obtain three-dimensional imaging spectrograms by using a scanning mirror in front of the spectrographic slit. The scanning mirror concept rotates by one step, the solar image on a slit moves by for example 70 microns, which corresponds to a width size of the slit. The imaging requires a lot of image frames for a single imaging spectrogram. However, it provides the opportunity creating spectrograms throughout a wide range of frequencies.

The slit also has the unique option if required of both a bilateral movement in sync with the rotary stage. This means that the slit assembly has the added option of a lateral movement. See Notes

The whole optical arrangement involves two separate buildings. The first building houses the heliostat with its own tracking system. The rays are projected horizontally from the heliostat to the second building, which has the optical system (Spectrograph). In between the two buildings is the movable achromat on motorized rail. The whole structure is about nearly 30 feet in length.

Status

The 35cm heliostat on a fork equatorial mount is near complete.
The mirror(1/4 lambda)I made awhile back. The mount uses 30cm dia. drive gear
The electronics/controller are complete for the mount.
The 20 cm achromat is complete. Used as the main periscope lens in the Hunter Killer submarines of the Royle Navy(made by Barr & Stroud,UK) High res lens.
The second building is complete.
The rail parts are complete and movable truck to hold lens assembly.
First building the foundations and walls are complete. Half built roof.
The rails from both buildings are complete. 30 feet in length.
The scanning mirror – mechanics are complete are designed and built, mirror needs coating.
The scanning mirror requires stepper motor-encoder configuration
The scanning mirror will require software development linked to slit.
The spectrograph bilateral slit and microcontroller and software is complete.
The grating is complete (Richardson Gratings, US).
The grating rotary table is designed and built, complete with microcontroller and software.
The collimator is built and working.
The receiving lens is complete and working

Note: The diffraction grating ruled area size is 102 x 128 mm. It is a 400-groove/mm plane reflectance grating blazed at 551 nm with a nominal 6.3-degree blaze angle. The grating has 90 per cent efficiency at its blaze angle and in first order from 5000 to 11000 Ångstroms the response stays above the 50 per cent grating efficiency points. In diffraction grating instruments such as this one, the first order image at any wavelength contains light from half that wavelength in the second order. When, for example, the spectrograph is to reach a maximum of 10,000 Ångstroms in the first order, wavelengths less than 5,000 Angstroms must be excluded.

Note: The spectral coverage of this instrument is between 300nm and 1000nm. Its optimum efficiency is in the 300-450nm range.

Note: It projects the incoming light through a horizontal moving slit assembly onto a reflective grating based on a rotary platform that is synchronised with the slit mechanism. The slit width is adjustable, as is the case in conventional spectrographs.

Note: An important part of the design is the lateral movement of the entire slit assembly (in addition to the movement of the slit itself), so that the narrow beam passing through the slit will reflect off different parts of the diffraction grating and be received by the camera in a scanning mode.

As you can appreciate there is a lot of work involved.
However, by designing and building yourself is very satisfying.
If everything goes well this year I may have first light.

Eamonn A

Sounds quite a project Eamonn and is coming together very well.
Looking forward to seeing the results of your efforts.