Outline for the creation of a Detector Laboratory

Scott D. Johnson


The goal is to characterize a scientific grade detector for use in an astronomical setting. The main purpose behind this exercise is to understand a portion of what each engineer in the major disciplines might do in designing a laboratory. Our goal will be to design this advanced laboratory. We will need to investigate cutting-edge material to achieve this. For the sake of clarity some subjects will have to be cursorily studied in class, but should be more fully studied outside of class.

The customer, an astronomer (scientist), has stated she wishes us to pick an appropriate detector for her astronomical purposes, test it for this purpose, and design the camera (instrument) along with components of a satellite to make this an effective astronomical tool at a high earth orbit. We will design the laboratory and advice the customer on the design of the satellite/camera.

The customer, who has a higher level scientific understanding then the typical engineer, wishes the detector to achieve the following specifications:

Dark Current requirements must be < 0.1 e-/pixel/sec

Read noise must be less than 4 e-

Astronomical parameters: ~0.5 arcsec for resolution and ~7' for a field of view.

Spectral range 500nm - 1000nm


Optics considerations:

We are looking to chose something like a CCD47-10 (grade 0) with 13 µm pitch, 1024x1024 pixels, and a spectral range of 400nm to 1100nm. However we would like to be sure and investigate other newer CCDs and maybe even CMOS devices.

We do not have a specific focal length or diameter of the telescope as the astronomer is going to leave that up to us in the first design phase.

If we assume an effective focal length of 5 m, we get a sampling resolution of about = arctan(13x10-6/5) = 0.54 arcsec and a field of view of = arctan(0.0133/5) = 9.14'. This should meet the astronomers requirements with a reasonable focal length of the telescope.

To assure ourselves that we are not diffraction limited we will need to make sure our diameter of the telescope is at least large enough to handle the 0.54 arcsec we wish to achieve. For practical purposes (since theory is in a perfect world) we will aim for 0.25 arcsec.

Given that we will calculate what we think would be a good diameter of the telescope. This will also give us an idea our our optical needs. We will need to discuss this with the astronomers to assure ourselves they will have the appropriate optics. The system will be more diffraction limited at the red-end of the spectrum, therefore we will only do this calculation for the 1000nm wavelength. Using a standard equation to calculate this.

0.25/(360*60*60/(2*pi)) = (1.22*1000*10-9)/x

x = 1.01 meters

Therefore an effective 5 meter focal length with a 1.01 meter diameter telescope should work.

To characterize the CCD given this focal length we will need optics with an f-number of 4.95 (f/4.95). It is unlikely we will be able to design a lab that will be able to handle optics as large as those prescribed so we will design f/4.95 optics and handle other issues in another manner. We will need an optical engineer to work with us on this design.

To achieve dark current of < 0.1 e-/pixel/sec we will need to cool our system to at least -75 C. We will achieve this using a dewar and a pulse tube cryocooler. Unfortunately our power requirements are limited on this mission. This necessitates a redesign of current pulse tube cryocoolers. We will need both a chemical engineer and possibly a mechanical engineer to help us on this portion of the laboratory.

To achieve a read noise of ~ 4 e- we will need to run the device at a clock speed below 250kHz. This slow speed may cause some problems with our dark current accumulation and our electronics will have to be designed for flexibility so that we can test different read out speeds (clock speed) along with different temperatures. There is a data acquisition system that might be able to handle this, but it likely will have to be at least partially redesigned. We will need to both and electrical engineer and a computer scientist on our team to help us with this work.

We also need a laboratory to begin with. Since we intend this laboratory to be useful beyond the current work, we would like a well designed vibration-free (as best as can be achieved) laboratory. We will need the services of a civil engineer to pick the best site and design the best usable building. We will need a mechanical engineer to help us design any quiet machinery within the building.

Finally we will act as a system engineer to design the whole system for characterization. We will design for this project, but keep in mind that we wish to utilize what we design after the project is completed. The resources are likely to be pretty expensive and doing a one-time project does not make sense for a laboratory.

Materials we should investigate and some starting web sites:

Detectors

Vibration considerations

Site considerations

Vibration tables

Telescopes

Cryogen System

Pulse Tube

Technical Equipment

DAQ