27-11-2012, 01:29 PM
SUMMER TRAINING PRESENTATION THE CCD DETECTOR
[attachment=41306]
Introduction
It seems that this near-infrared (8900 Å) picture of Uranus was the first celestial object to be photographed by a CCD in 1975 by astronomers at the JPL and University of Arizona.
This image has been obtained by the 61 inch telescopes located at Santa Catalina mountains near Tucson (Arizona).
The dark region in the image correspond to an absorption region with some Methane bands close to the southern pole of Uranus.
History
In 1969 Willard S. Boyle and George E. Smith, while working at Bell Laboratories, designed the first Charge Coupled Device (CCD), a working version was produced just a year later.
The CCD has become the bedrock of the digital imaging revolution including digital photography and video. In January 2006 they have been honored with the Charles Stark Draper Prize which is presented by the National Academy of Engineering.
What is a CCD ?
Charge Coupled Devices (CCDs) were invented in the 1970s and originally found application as
memory devices. Their light sensitive properties were quickly exploited for imaging applications
and they produced a major revolution in Astronomy. They improved the light gathering power of
telescopes by almost two orders of magnitude. Nowadays an amateur astronomer with a CCD camera
and a 15 cm telescope can collect as much light as an astronomer of the 1960s equipped with a
photographic plate and a 1m telescope.
CCDs work by converting light into a pattern of electronic charge in a silicon chip. This pattern of
charge is converted into a video waveform, digitised and stored as an image file on a computer.
Structure of a CCD (1)
CCDs are are manufactured on silicon wafers using the same photo-lithographic techniques used
to manufacture computer chips. Scientific CCDs are very big ,only a few can be fitted onto a wafer.
This is one reason that they are so costly.
The photo below shows a silicon wafer with three large CCDs and assorted smaller devices. A CCD has
been produced by Philips that fills an entire 6 inch wafer! It is the worlds largest integrated circuit.
How does a CCD work? (1)
Determining the distribution of an astronomical object (star, planet, galaxy, a martian spacecraft (?)) with the help of a CCD is similar to measuring the quantity of infalling rain on a field.
As soon as the rain stops, collecting buckets are displaced horizontally on conveyor belts. Then the water content of the buckets is collected in other buckets on a vertical conveyor belt. The overall content is sent onto a weighting system.
The way a CCD works is illustrated by means of a simplified CCD made out of 9 pixels, an output register and an amplifier.
Each pixel is divided into 3 regions (electrodes who create a potential well).
(a) For the charge collection process during an exposure the central electrode of each pixel is maintained at a higher potential (yellow) than the others (green).
(b) At the end of the exposure, the electrodes’ potentials are changed and the charges transferred from one electrode to the other.
[attachment=41306]
Introduction
It seems that this near-infrared (8900 Å) picture of Uranus was the first celestial object to be photographed by a CCD in 1975 by astronomers at the JPL and University of Arizona.
This image has been obtained by the 61 inch telescopes located at Santa Catalina mountains near Tucson (Arizona).
The dark region in the image correspond to an absorption region with some Methane bands close to the southern pole of Uranus.
History
In 1969 Willard S. Boyle and George E. Smith, while working at Bell Laboratories, designed the first Charge Coupled Device (CCD), a working version was produced just a year later.
The CCD has become the bedrock of the digital imaging revolution including digital photography and video. In January 2006 they have been honored with the Charles Stark Draper Prize which is presented by the National Academy of Engineering.
What is a CCD ?
Charge Coupled Devices (CCDs) were invented in the 1970s and originally found application as
memory devices. Their light sensitive properties were quickly exploited for imaging applications
and they produced a major revolution in Astronomy. They improved the light gathering power of
telescopes by almost two orders of magnitude. Nowadays an amateur astronomer with a CCD camera
and a 15 cm telescope can collect as much light as an astronomer of the 1960s equipped with a
photographic plate and a 1m telescope.
CCDs work by converting light into a pattern of electronic charge in a silicon chip. This pattern of
charge is converted into a video waveform, digitised and stored as an image file on a computer.
Structure of a CCD (1)
CCDs are are manufactured on silicon wafers using the same photo-lithographic techniques used
to manufacture computer chips. Scientific CCDs are very big ,only a few can be fitted onto a wafer.
This is one reason that they are so costly.
The photo below shows a silicon wafer with three large CCDs and assorted smaller devices. A CCD has
been produced by Philips that fills an entire 6 inch wafer! It is the worlds largest integrated circuit.
How does a CCD work? (1)
Determining the distribution of an astronomical object (star, planet, galaxy, a martian spacecraft (?)) with the help of a CCD is similar to measuring the quantity of infalling rain on a field.
As soon as the rain stops, collecting buckets are displaced horizontally on conveyor belts. Then the water content of the buckets is collected in other buckets on a vertical conveyor belt. The overall content is sent onto a weighting system.
The way a CCD works is illustrated by means of a simplified CCD made out of 9 pixels, an output register and an amplifier.
Each pixel is divided into 3 regions (electrodes who create a potential well).
(a) For the charge collection process during an exposure the central electrode of each pixel is maintained at a higher potential (yellow) than the others (green).
(b) At the end of the exposure, the electrodes’ potentials are changed and the charges transferred from one electrode to the other.