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- Photomultiplier Modules (PMTs)
- Можно ли навесить фасад без пароизоляции
- Connectors on PMT Module
- Как правильно вести вкликий пост
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Photomultiplier tubes PMTs are used to detect faint optical signals from weakly emitting sources. Compared to avalanche photodetectors APDs , they offer significantly larger active areas, making them ideal for capturing signals that may be diverging due to scatter or nonlinear optical effects.
This software package includes. This potential causes the electrons to strike several dynodes that generate secondary electrons. The photocurrent that has accumulated after the final dynode stage represents the amplified signal and is collected by an anode.
See the PMT Tutorial tab for more details. The photocurrent collected at the anode is typically sent into a transimpedance amplifier that converts the current into a voltage and provides additional amplification. They are compatible with our TIA60 Transimpedance Amplifier , as well as other transimpedance amplifiers, which are available separately.
This cable is pictured in the Shipping List tab.
These cables are pictured in the Shipping List tab. These PMT modules ship with a male M8 x 1 connector with colored wire leads. This connector is pictured in the Shipping List tab. The most recent firmware for these PMTs is available as well.
Introduction Since the first commercial photomultiplier tube PMT was developed in the early s, it has remained the detector of choice for experiments requiring fast response times and high sensitivity.
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Today, the PMT is a staple for research in many fields including analytical chemistry, particle physics, medical imaging, industrial process control, astronomy, and atomic and molecular physics. This tutorial provides introductory material for the principle of operation and key specifications to consider when choosing a PMT for a given application. Basic Principle of Operation Photomultiplier Tubes PMTs are sensitive, high-gain devices that provide a current output that is proportional to the incident light.
The PMT consists of a glass vacuum tube that houses a photoemissive material called a photocathode, 8 - 14 secondary emitting electrodes called dynodes, and a collection electrode called an anode. If a photon with sufficiently high energy i. Since the first dynode is maintained at a higher potential than the cathode thereby creating a potential difference between these two elements , the ejected electron will accelerate toward the dynode and crash into it, releasing secondary electrons.
Typically, 3 - 5 secondary electrons are released during this process. Each of these 3 - 5 electrons is then in turn accelerated toward and crashes into the second dynode, thereby releasing 3 - 5 more electrons. This process continues through the entire dynode chain providing an electron gain of 3 - 5. Typically, each dynode is maintained at a potential that is - V higher than the previous one. At the end of the dynode chain, the electrons are collected by the anode and a current pulse is output.
Photomultiplier Modules (PMTs)
However, to read that pulse, the current usually needs to be converted to a voltage; the simplest way to do this is to connect a low load resistance across the anode and ground. If the capacitance is 5 pF, the output voltage pulse will be 2. Spectral Response When choosing a PMT for a given application, the photocathode material should be matched to the intended application. Generally, the long-wavelength cutoff is determined by the photocathode, while the window material determines the short-wavelength cutoff.
PMTs are manufactured for wavelengths from the deep UV through the infrared. However, since the photocathode is responsible for converting incident photons into electrons, the efficiency with which it does this for the wavelength of interest is of utmost importance. There are a variety of materials used for photocathodes, each with a different work function and each intended for use in a different spectral range.
Quantum Efficiency QE is a specification that is usually expressed as a percentage and is associated with the PMTs ability to convert incident photons into detectable electrons. Since QE is dependent upon wavelength, it is important to choose a PMT with the best quantum efficiency over the wavelength range of interest.
The QE of a PMT can be quickly calculated from its spectral response plot see the Graphs t ab by using the following equation:. Geometries PMTs are available primarily with two different geometries: head-on i. Head-on PMTs have semitransparent photocathodes and are characterized by large collection surfaces, better spatial uniformity, and better performance in the blue and green spectral regions.
For applications requiring a wide spectral response, such as spectroscopy, the head-on geometry is preferable. This configuration tends to be less expensive than head-on and is widely used in spectrometers and for applications requiring efficient optical coupling and high QE such as scintillation counting.
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The 8 - 14 secondary emitting electrodes i. Linear dynode arrays such as the one shown in the figure above are popular due to their fast time response, good time resolution, and excellent pulse linearity. This configuration is compact and offers fast response times. Gain PMTs are unique because they are capable of amplifying very weak signals produced by photocathodes to detectable levels above the readout circuitry noise without introducing substantial noise. In a PMT, the dynodes are responsible for producing this amplification, which is referred to as gain.
Gain is highly dependent on the voltage being applied. Dark Current Ideally, all of the signal produced by a photocathode would be due to current generated by light incident on the tube. However, in reality, PMTs will produce currents regardless of whether light is present. The signal that results in the absence of light is known as dark current, and it effectively degrades the signal-to-noise ratio of the PMT.
Dark current is due mainly to the thermionic emission of electrons from the photocathode and first few dynodes but with far smaller contributions from cosmic rays and radioactive decay.
In general, tubes designed for use in the red part of the spectrum will exhibit more dark current than others due to the lower binding energy of red-sensitive photocathodes. If it is assumed that the primary source of dark current is thermionic emission from the photocathode, the dark count rate is given by:. When using a thermoelectric cooler, care should be taken to avoid condensation at the window since this moisture will reduce the amount of light incident on the photocathode.
Connectors on PMT Module
In addition, excessive cooling should be avoided, as it can actually have adverse effects. These effects include signal reduction or voltage drops across the cathode, since the resistance of the cathode film is inversely proportional to the temperature. Rise Time For experiments demanding high time resolution, short rise times are a must. Ultimately, the pulse rise time is determined by the spread in transit times for the different electrons.
These times vary for several reasons.
First, the initial velocities of secondary electrons will vary because they are released from different depths within the dynode material. Some electrons will have no initial energy when leaving the dynode whereas other will have a non-zero initial energy; hence, the latter arrive at the next dynode in a shorter time period. In addition to the variation in initial ejected electron speed, transit time spread is also caused by electron path length variations.
Other Considerations There are several other important considerations. First, choose the electronics that will be used with the PMT carefully. Small changes in the high voltage applied across the cathode and anode can dramatically change the output.
Second, the lab environment can also affect the performance of the PMT.
Как правильно вести вкликий пост
Changes in temperature and humidity as well as the presence of vibrations all negatively affect tube operation. Magnetic fields of a few gauss can greatly reduce the gain, but these adverse affects can be minimized by creating a magnetic shield from a high permeability material. Each package provides different types of output signals and mechanical mounting features. The Graphs tab contains a plot comparing the radiant sensitivity of each PMT; the radiant sensitivity is closely related to the quantum efficiency.
Complete specifications are available in the Specs tab above. Their built-in transimpedance amplifiers allow them to directly provide output voltage signals through an SMA connector. The control voltage that biases the PMT is provided through a 2.
Each module ships with a 2. The photocathode is located behind internal SM1 threads. Direct filter mounting is not recommended because the filter will be in contact with the window.
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Replacement power supplies are sold below. These PMTs are offered in two package styles, providing a range of mechanical mounting options. Please contact Tech Support if you wish to integrate these PMTs with existing Thorlabs confocal and multiphoton systems. It provides an output current through a BNC connector. The control voltage that biases the PMT is provided through a female M8 x 1 connector.
Each module ships with a male M8 x 1 connector with leads that can be wired by the user to an appropriate low-noise voltage source. The photocathode is located behind internal C-Mount threads. The threads on the PMT module are not deep enough to directly accommodate a filter with a retaining ring. No power supply is included with this PMT.
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See the Pin Diagrams and Shipping List tabs for details. The GaAsP photocathode provides a high quantum efficiency in the visible spectrum, resulting in an elevated sensitivity to incoming illumination versus photocathodes composed of alkali metals see the Overview for a graph of the radiant sensitivity, which is proportional to the quantum efficiency. In addition, these PMT modules utilize a wide collection angle, further enhancing light detection see the image to the right.
Note that, if exposed to high intensity incident light, sensitivity degradation is more likely to occur compared to alkali PMTs. They are also powered by a USB 2. The input port of the PMTSS2 module has a fiber collimation assembly with an SMA connector, which accepts signals that have been coupled into a multimode fiber patch cable or bundle.
If desired, the collimation assembly can be unthreaded to allow the module to accept free-space signals. If using the included fiber input, a maximum of eight channels is recommended in order to prevent beam divergence from causing inefficient signal detection. Due to the weight of these modules, we only recommend direct table mounting.
No power supplies are included with these PMT modules.
As shown in the diagram to the right, the 2 m 6. A region-specific power cord is shipped with the unit. Close [X]. Related Items Scientific-Grade Cameras. Neutral Density Filters.