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A wavelength shifter is a photofluorescent material that absorbs higher frequency photons and emits lower frequency photons. The material absorbs one photon, and emits one or multiple lower-energy photons. The relaxation time of the excited molecule is usually in the order of nanoseconds.
Wavelength shifters are often used in particle physics to collect scintillation or Cherenkov light in particle detectors. Materials, such as acrylic slaps or optical fibers, are typically either doped with wavelength-shifting molecules or coated with wavelength-shifting paint. [1] [2] [3]
Wavelength-shifting technology is of particular interest for low-background supernova neutrino detectors such as IceCube, [4] [5] Super-Kamiokande [6] or its successor Hyper-Kamiokande. [7] Here, wavelength shifters offer two advantages: As these types of detectors are based on the emission of Cherenkov radiation from secondary particles traveling faster than the phase velocity of light in the medium from the neutrino interaction, absorbing more photons in the UV range and shifting them to the visible range detectable by conventional PMTs is beneficial. In addition, with wavelength shifters larger collection areas can be covered price-efficiently as compared to standard PMT-based sensors. An example of a sensor making use of wavelength-shifting technology is the Wavelength-shifting Optical Module (WOM) [8] [9] envisaged for an extension of the IceCube detector.
Furthermore, wavelength shifting materials can be used to increase the efficiency of a photovoltaic cell (solar cell) by changing one "too-high" energy photon into multiple "just-right" energy photons.
Besides the scientific application, wavelength shifters are sometimes used to achieve UV resistance of plastics instead of absorbers. Wavelength shifter are also used to shift UV light to the visible spectrum in Fluorescent lamps or LEDs, in most cases this is done with a Phosphor that can be considered a wavelength shifter with a long (ms) relaxation time.
Organic wavelength shifters usually contain one or more benzene-ring(s) (e.g. de:1,4-Bis(2-methylstyryl)benzol or p-Terphenyl) since the and bonds here are useful in the absorption/emission of the photon and the energy transport within the molecule. Modifications of the molecules allow in some cases the tuning of the acceptance and emission wavelength regime. The wavelength shift occurs due to the Franck–Condon principle, while excess energy is usually carried away in form of phonons.
Most organic wavelength shifters are planar molecules, causing a decrease in wavelength shifting efficiency when crystallized due to energy exchange between the molecules. Current research has also created 3 dimensional wavelength shifters that show the opposite effect since clustering together limits the energy that can be stored as rotational energy. [ citation needed ]
Wavelength shifter usually have many absorption and emission lines that are broad enough to create an absorption and emission spectrum. The separation between absorption and emission spectrum is defined by the so-called Stokes shift.
An optical spectrometer is an instrument used to measure properties of light over a specific portion of the electromagnetic spectrum, typically used in spectroscopic analysis to identify materials. The variable measured is most often the irradiance of the light but could also, for instance, be the polarization state. The independent variable is usually the wavelength of the light or a unit directly proportional to the photon energy, such as reciprocal centimeters or electron volts, which has a reciprocal relationship to wavelength.
The emission spectrum of a chemical element or chemical compound is the spectrum of frequencies of electromagnetic radiation emitted due to electrons making a transition from a high energy state to a lower energy state. The photon energy of the emitted photons is equal to the energy difference between the two states. There are many possible electron transitions for each atom, and each transition has a specific energy difference. This collection of different transitions, leading to different radiated wavelengths, make up an emission spectrum. Each element's emission spectrum is unique. Therefore, spectroscopy can be used to identify elements in matter of unknown composition. Similarly, the emission spectra of molecules can be used in chemical analysis of substances.
Absorption spectroscopy is spectroscopy that involves techniques that measure the absorption of electromagnetic radiation, as a function of frequency or wavelength, due to its interaction with a sample. The sample absorbs energy, i.e., photons, from the radiating field. The intensity of the absorption varies as a function of frequency, and this variation is the absorption spectrum. Absorption spectroscopy is performed across the electromagnetic spectrum.
A scintillator is a material that exhibits scintillation, the property of luminescence, when excited by ionizing radiation. Luminescent materials, when struck by an incoming particle, absorb its energy and scintillate. Sometimes, the excited state is metastable, so the relaxation back down from the excited state to lower states is delayed. The process then corresponds to one of two phenomena: delayed fluorescence or phosphorescence. The correspondence depends on the type of transition and hence the wavelength of the emitted optical photon.
Fluorescence spectroscopy is a type of electromagnetic spectroscopy that analyzes fluorescence from a sample. It involves using a beam of light, usually ultraviolet light, that excites the electrons in molecules of certain compounds and causes them to emit light; typically, but not necessarily, visible light. A complementary technique is absorption spectroscopy. In the special case of single molecule fluorescence spectroscopy, intensity fluctuations from the emitted light are measured from either single fluorophores, or pairs of fluorophores.
In physics and physical chemistry, time-resolved spectroscopy is the study of dynamic processes in materials or chemical compounds by means of spectroscopic techniques. Most often, processes are studied after the illumination of a material occurs, but in principle, the technique can be applied to any process that leads to a change in properties of a material. With the help of pulsed lasers, it is possible to study processes that occur on time scales as short as 10−16 seconds. All time-resolved spectra are suitable to be analyzed using the two-dimensional correlation method for a correlation map between the peaks.
Neutrino astronomy is the branch of astronomy that observes astronomical objects with neutrino detectors in special observatories. Neutrinos are created as a result of certain types of radioactive decay, nuclear reactions such as those that take place in the Sun or high energy astrophysical phenomena, in nuclear reactors, or when cosmic rays hit atoms in the atmosphere. Neutrinos rarely interact with matter, meaning that it is unlikely for them to scatter along their trajectory, unlike photons. Therefore, neutrinos offer a unique opportunity to observe processes that are inaccessible to optical telescopes, such as reactions in the Sun's core. Neutrinos can also offer a very strong pointing direction compared to charged particle cosmic rays.
The Antarctic Muon And Neutrino Detector Array (AMANDA) is a neutrino telescope located beneath the Amundsen–Scott South Pole Station. In 2005, after nine years of operation, AMANDA officially became part of its successor project, the IceCube Neutrino Observatory.
A solar neutrino is a neutrino originating from nuclear fusion in the Sun's core, and is the most common type of neutrino passing through any source observed on Earth at any particular moment. Neutrinos are elementary particles with extremely small rest mass and a neutral electric charge. They only interact with matter via the weak interaction and gravity, making their detection very difficult. This has led to the now-resolved solar neutrino problem. Much is now known about solar neutrinos, but the research in this field is ongoing.
The IceCube Neutrino Observatory is a neutrino observatory constructed at the Amundsen–Scott South Pole Station in Antarctica. The project is a recognized CERN experiment (RE10). Its thousands of sensors are located under the Antarctic ice, distributed over a cubic kilometre.
A neutrino detector is a physics apparatus which is designed to study neutrinos. Because neutrinos only weakly interact with other particles of matter, neutrino detectors must be very large to detect a significant number of neutrinos. Neutrino detectors are often built underground, to isolate the detector from cosmic rays and other background radiation. The field of neutrino astronomy is still very much in its infancy – the only confirmed extraterrestrial sources as of 2018 are the Sun and the supernova 1987A in the nearby Large Magellanic Cloud. Another likely source is the blazar TXS 0506+056 about 3.7 billion light years away. Neutrino observatories will "give astronomers fresh eyes with which to study the universe".
Radio Ice Cherenkov Experiment (RICE) was an experiment designed to detect the Cherenkov emission in the radio regime of the electromagnetic spectrum from the interaction of high energy neutrinos with the Antarctic ice cap. The goals of this experiment are to determine the potential of the radio-detection technique for measuring the high energy cosmic neutrino flux, determining the sources of this flux, and measuring neutrino-nucleon cross sections at energies above those accessible with existing accelerators. Such an experiment also has sensitivity to neutrinos from gamma ray bursts, as well as highly ionizing charged particles traversing the Antarctic icecap.
T2K is a particle physics experiment studying the oscillations of the accelerator neutrinos. The experiment is conducted in Japan by the international cooperation of about 500 physicists and engineers with over 60 research institutions from several countries from Europe, Asia and North America and it is a recognized CERN experiment (RE13). T2K collected data within its first phase of operation from 2010 till 2021. The second phase of data taking (T2K-II) is expected to start in 2023 and last until commencement of the successor of T2K – the Hyper-Kamiokande experiment in 2027.
Hyper-Kamiokande is a neutrino observatory and experiment under construction, conducted in Japan by the collaboration of institutes from 21 countries from six continents. As a successor of the Super-Kamiokande (SK) and T2K experiments, it is designed to search for proton decay and detect neutrinos from natural sources such as the Earth, the atmosphere, the Sun and the cosmos, as well as to study neutrino oscillations of the man-made accelerator neutrino beam. The beginning of data-taking is planned for 2027.
The Askaryan Radio Array (ARA) is a new detector designed to detect a few GZK neutrinos a year. It measures the enhanced radio-frequency radiation emitted during the interaction of the neutrino in Antarctic ice sheet. The detection is based on the Askaryan effect, an idea by Gurgen Askaryan
David Saltzberg is a professor of physics and astronomy at the University of California, Los Angeles. Saltzberg received a Sloan Fellowship, NSF Career Award, and Department of Energy Outstanding Junior Investigator Award while an assistant professor. Saltzberg earned a bachelor's degree in physics in 1989 from Princeton University and a Ph.D. in physics from the University of Chicago in 1994. From 1995-97 he worked at CERN in Switzerland. His research interests include high-energy collider physics and the radio detection of cosmic neutrinos.
Antarctic Ross Ice-Shelf Antenna Neutrino Array (ARIANNA) is a proposed detector for ultra-high energy astrophysical neutrinos. It will detect coherent radio Cherenkov emissions from the particle showers produced by neutrinos with energies above about 10^17 eV. ARIANNA will be built on the Ross Ice Shelf just off the coast of Antarctica, where it will eventually cover about 900 km^2 in surface area. There, the ice-water interface below the shelf reflects radio waves, giving ARIANNA sensitivity to downward going neutrinos and improving its sensitivity to horizontally incident neutrinos. ARIANNA detector stations will each contain 4-8 antennas which search for brief pulses of 50 MHz to 1 GHz radio emission from neutrino interactions.
The LUX-ZEPLIN (LZ) Experiment is a next-generation dark matter direct detection experiment hoping to observe weakly interacting massive particles (WIMP) scatters on nuclei. It was formed in 2012 by combining the LUX and ZEPLIN groups. It is currently a collaboration of 30 institutes in the US, UK, Portugal and South Korea. The experiment is located at the Sanford Underground Research Facility (SURF) in South Dakota, and is managed by the United States Department of Energy's (DOE) Lawrence Berkeley National Lab.
The Accelerator Neutrino Neutron Interaction Experiment (ANNIE) is a proposed water Cherenkov detector experiment designed to examine the nature of neutrino interactions. This experiment will study phenomena like proton decay, and neutrino oscillations, by analyzing neutrino interactions in gadolinium-loaded water and measuring their neutron yield. Neutron Tagging plays an important role in background rejection from atmospheric neutrinos. By implementing early prototypes of LAPPDs, high precision timing is possible. The suggested location for ANNIE is the SciBooNE hall on the Booster Neutrino Beam associated with the MiniBooNE experiment. The neutrino beam originates in Fermilab where The Booster delivers 8 GeV protons to a beryllium target producing secondary pions and kaons. These secondary mesons decay to produce a neutrino beam with an average energy of around 800 MeV. ANNIE will begin installation in the summer of 2015. Phase I of ANNIE, mapping the neutron background, completed in 2017. The detector is being upgraded for full science operation which is expected to begin late 2018.
