It's official: a physicist's laboratory is the coldest place in the universe. Physicists and physical chemists are finding that having the coldest place in the universe is becoming increasingly useful. Small collections of atoms or ions cooled to ultra-low temperatures provide the ideal laboratory for a wide variety of applications, including the study of fundamental physics, the development of sensors and ultra-precise time clocks and possibly the development of a future generation of supercomputers.
Bose-Einstein condensation describes the collapse of the atoms into a single quantum state. This phenomenon was predicted in the 1920's, and derived originally from Satyendra Bose's work on the statistical mechanics of photons, and subsequently formalized by Albert Einstein. Governed by the Bose-Einstein statistics, a Bose gas describes the statistical distribution of certain types of identical particles known as bosons. "Bosonic particles", are allowed to share quantum states with each other.
Einstein speculated that cooling bosonic atoms to a very low temperature, to beyond a "critical temperature" for the atom, would cause them to condense into the lowest available quantum state, resulting in a new wavelike form. In this state, a cloud of atoms will form a macroscopic quantum state in which all the atoms share the same space and have phase coherence in their wavefunctions.
Thus, as the value for momentum becomes more certain, the position of the atoms becomes more uncertain or (in quantum mechanical terms), the wavepacket that describes an individual atom becomes "delocalized".
Heisenberg's uncertainty principle
As the atoms cool down, their kinetic energy and hence their momentum reduce. Heisenberg's uncertainty principle (as shown on the right) confirms this.
Δx = the uncertainty in the measured value of positionΔp = the uncertainty in the measured value of a component of momentumħ = reduced Planck constant
Laser cooling can reduce the temperatures of atoms to a few billionths of a degree above the coldest temperature it is possible to achieve: absolute zero Kelvin (-273.15°C). This environment created in the laboratory is even colder than the most remote regions of deep space, which are pervaded by cold microwave radiation - the afterglow of the big bang. So, advanced techniques are evolving to create, trap and manipulate such novel states - another challenge is to see them.
Andor high-performance CCD and Electron Multiplying CCD (EMCCD) camera solutions have been a key component to dedicated set-ups throughout the world, aimed at creating and detecting Bose Einstein Condensates.The challenging detection requirements associated with typical optical configurations for laser-cooling have been addressed though a number of particular operational modes of Andor cameras, including combinations of the following:
Some of these modes are described in more detail later in this section.
QE curves relevant to Bose Einstein
Andor's pioneering iXonEM+ is a revolutionary range of CCD cameras that provides single photon detection sensitivity, highest QE and -100°C Thermoelectric (TE) cooling at rapid frame rates, utilizing Andor's pioneering and award-winning EMCCD technology.
Andor's LucaEM is the latest EMCCD innovation, a highly cost-effective option making EMCCD available to every application. Operate "gain off" for conventional CCD operation under brighter conditions - turn on the EM gain when the photons become scarce!LucaEM DL-658M provides single photon detection sensitivity and 52% QE at 30 full frames/sec, in a cooled USB 2.0 platform.
LucaEM
The LucaEM DL-658M houses a 658 (H) x496 (V) interline sensor, offering single photon sensitivity, ~ 52% QE, 10 x 10μm pixel size and USB 2.0 interface @ 30 full frames/sec.
Whilst back illumination undoubtedly offers the highest QE across the entire spectral range, when imaging beyond 780nm, it is often prudent to potential consider etaloning effects of back illuminated sensors. The extent of the resulting fringing patterns can depend on optical factors such as the parallel nature of light impinging on the sensor and of the relative shot noise of the signal. The Virtual Phase (VP) front illuminated iXonEM+ DU-885 can be a popular choice to ensure that such fringing is completely eradicated from signals at such long probe wavelengths, whilst still maintaining relatively high QE across the entire wavelength range.Alternatively, if QE in the near IR is of utmost importance, Andor's back illuminated deep-depletion imaging CCD camera, the iKon-M DV-934-BRD offers 90% QE @ 780nm on a 1k x 1k imaging sensor format.
Andor's iKon-M CCD range offers affordable, yet unmatched sensitivity for slow scan astronomy. The iKon-M platform houses a range of full frame and frame transfer sensors, in both front-illuminated and back-illuminated (>90% QE) varieties.
For highest QE @ 780nm, we recommend the new line iKon-M DU-934N-BRD. Andor's BRD cameras are currently the only back-illuminated Deep Depletion sensors that incorporate Fringe Suppression Technology, to minimise etaloning/fringing effects. The 1024 x 1024 array boasts high resolution 13μm2 pixels. The system also benefits from negligible dark current with thermoelectric cooling down to -100°C, coupled with low readout noise of 2 to 3 electrons rms.
Illustration of fast kinetics acquisition mode
The absolute maximum time-resolution affordable from an EMCCD is available in this readout mode. Illustrated here for fast spectroscopy, fast kinetics can also be used for imaging at μs time resolution. Andor's EMCCDs have industry fastest parallel (vertical) shift speeds (sub μs available), and can be harnessed to optimal effect in this readout mode. In this configuration, the imaged area is focused onto a user-defined number of rows at the very top of the sensor. The "dark rows" beneath are subsequently used for storing the images shifted down from the exposed area, reaching time resolution down to 0.4μs/row.
A new unique feature enables the user to use signal accumulated in the exposed are also, provided the probe pulse can be rapidly switched off prior to readout, hence affording an extra image - this can be important if only dividing the entire image area into 4 segments. Vertical shift timings can be either driven by camera or by external trigger pulses.
Illustration of cropped sensor acquisition mode
In this mode, we can "fool" the sensor into thinking it is smaller than it actually is, and readout continuously at a much faster frame rate. For example, by focusing an image onto a 10 x 1000 area at the bottom of iXonEM+ DU-885at 35 MHz pixel readout, one can readout up to 3500 images/sec.
If your experiment dictates that you need fast time resolution but cannot be constrained by the storage size of the sensor, then it is possible to readout the EMCCD in a "cropped sensor" mode, as illustrated on the left.
It is a fundamental need of many atom-cooling experiments, to be able to "expel" light collected from bright "set-up" lasers, immediately prior to introduction of probe lasers.
With the iXonEM+ DU-885, Andor have adapted the anti-bloom structure inherent to the Texas Instruments frame transfer Impactron sensor, to "flush" charge from the sensor when not exposing. The time to switch to an exposure is in the order of a microsecond. The end of an exposure begins the shift of the image underneath the FT mask. This functionality has been extended to bulb mode acquisition. In bulb mode, the beginning and end of exposure is determined by the rising and falling edges of an external trigger. This trigger can be synchronized to coincide exactly with the probe pulse.
In iXonEM+ cameras housing L3 sensors from E2V, Andor have implemented a readout mode whereby unwanted charge (i.e. during cleaning cycles and sub-array selection) is purged straight from the serial (or "shift") register , therefore it is not readout through the EM gain register and amplifier electronics as the image pixels would.
Andor have adapted the true microsecond "electronic gating" capability of the new Texas Instruments interline Impactron sensor. This uses the anti-bloom structure to "flush" charge from the sensor when not exposing, and the interline masked columns to rapidly shift charge under at the end of an exposure. This is combined with external trigger in a bulb mode, as for the iXonEM+ DU-885.
Images supplied by Chapman Research Labs, Prof. Michael Chapman's research group at the School of Physics, Georgia Institute of Technology (Georgia Tech) in Atlanta, Georgia.
Prof Chapman's research is focused on investigating the quantum behavior of atoms and photons, often at the single particle level. Lasers are employed to confine and cool atoms to nano-Kelvin temperatures, which are used for studies including fundamental atom-photon interactions, atom optics and interferometry, and quantum computing and communication.
A Bose-Einstein condensate of 17,000 rubidium-87 atoms is created directly in a 1-D optical lattice formed by two counter-propagating CO2laser beams. The absorption image shown here here is taken 10 ms after the condensate is released from the optical trap.
Fluorescent image of 1000 atoms that are transported by an optical dipole force trap into a high finesse microcavity.
Fluorescent images of magneto-optical trap (MOT) containing 0 - 4 atoms. iXon DV-887 used with 4x4 pixel binning.
Time trace derived from small number of atoms in magneto- optical trap.
Low-light fluorescence image of one million trapped rubidium atoms cooled to micro Kelvin temperatures. The gaseous atoms are confined at the intersection of three focused, off-resonant laser beams, and the image was taken by briefly illuminating the atoms with resonant laser light.
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