Computer controlled deformable mirrors can correct, in real-time, the distortion caused by the turbulence of the Earth’s atmosphere, making the images obtained almost as sharp as those taken in space.
Adaptive optics require a bright reference star that is very close to the object under study.
This reference star is used to measure the blurring caused by the local atmosphere so that the deformable mirror can correct for it. Since suitable stars are not available everywhere in the night sky, astronomers can create an artificial star instead by shining a powerful laser beam into the Earth’s upper atmosphere. Thanks to these laser guide stars, almost the entire sky can now be observed with adaptive optics.
Recent technological changes in CMOS cameras now permit short exposures to be taken with negligible read out noise, allowing a high-speed stream of images to be captured. This can result in thousands of quick short exposures being saved for post processing.
This technique uses a bright star nearby the object to be observed, and calculation of the Strehl number of the reference star in each image taken. A selection algorithm drops images that fall below the minimum and those images that meet the selection criteria are used and this may be as little as 1% to 10% of the data stream. These selected images are combined by shifting and co-adding the sequence to produce diffraction limited image of the object being observed. The resultant image has been corrected for the turbulence of the atmosphere. This technique has also been called ”LUCKY IMAGING”. Associated techniques are “speckle interferometry”.
EUV / VUV detectors are used for calculating the fractional abundance of ions for hot plasmas with different electron temperatures and electron densities.
They are used to characterise wavelengths and the emissivity versus temperature of the brightest spectral lines emitted by ions with wavelengths longer than 45 Å. ITER plasmas can be analysed using selected EUV lines, similar to the space-based instruments routinely used to study temperatures, emission lines and motions of 0.1–2 keV solar coronal plasmas.
It is important to match the detector yield over the entire spectral range whilst maintaining good spatial as well as temporal resolution. It is possible to use direct and indirect detection. Direct detection is achieved by selecting back thinned CMOS sensors in order to optimise quantum efficiency in the range of 100 eV and above. With a band gap of 3.5 eV on average, each photon is well discriminated, however coping with bright signals can be issue. Indirect detection can be used with either an MCP or phosphor screen assembly read out by a CMOS detector with giving a better compromise on dynamic range.
Quantum dots (QDs) are tiny semiconductor particles a few nanometres in size that have optical and electronic properties that differ from larger particles due to the quantum behaviour at nanoscales.
They are a central topic in nanotechnology. When quantum dots are illuminated by UV light, an electron in the quantum dot can be excited to a state of higher energy.
In the case of a semiconducting quantum dot, this process corresponds to the transition of an electron from the valence band to the conductance band. The excited electron can drop back into the valence band releasing its energy by emitting light.
A scanning electron microscope (SEM) produces images of a sample by scanning the surface with a focused beam of electrons.
The electrons interact with atoms in the sample, producing various signals that contain information about the surface topography and composition of the sample. The electron beam is scanned in a raster scan pattern, and the position of the beam is combined with the intensity of the detected signal to produce an image.
Back scattered electrons diffracted from a stationary beam will create a pattern that can be captured by a CMOS camera that will unveil microstructural information such as grain orientation, phase and texture.
The TEM is used heavily in both material science / metallurgy and the biological sciences.
In both cases, the specimens must be very thin and able to withstand the high vacuum present inside the instrument.
Electrons are transmitted through an ultra-thin specimen, interacting with the specimen as it passes through it. An image is formed from the electrons transmitted through the specimen, magnified and focused by an electron lens and appearing as an image on a fluorescent screen coupled to a high-resolution CCD camera.
Spatial resolution and dynamic range are important because of the high intensity distribution across the image, especially during diffraction experiments. The ability to adapt speed of acquisition and dynamic range is required when acquiring fast structural data sets with cryogenically cooled samples.
Fibre optic coupling combined with proprietary scintillator deposition allows the optimum detective quantum efficiency and optimum resolution to be achieved from 70 up to >200 kV operation.