amplitude converter, data analyzer, digitizer, transient recorder, analog-to-digital converter
Analog-to-digital Converters are circuits that quantize a voltage or current into a stream of digital data. Board level products that make ADCs with sample rates of hundreds of Mega samples per Seconds (Msps) or several Giga samples per seconds (Gsps) accessible to the software are often called "digitizers" or "transient recorders". Unlike other ADC boards, our digitizers are optimized to detect pulses on the fly and stream the extracted sample data directly to the main memory, minimizing latency and CPU load. This is enabled by our custom 6GByte/s PCIe DMA controller that manages the buffer data structures directly without software intervention.
An averager is an ADC digitizer that does not present single acquired waveforms to the user but does calculate the average of multiple waveforms before readout. This greatly reduces the amount of data that needs to be read out. It also takes away flexibility and makes it impossible to do processing on the individual pulses to improve the measurement results. Our Ndigo6G implements zero suppression together with very high readout bandwidth to enable software-based averaging without losing the ability to operate on individual pulses. Contact us to talk about the option of performing hardware averaging in the Ndigo6G.
Avalanche photodiodes are highly sensitive, fast photodiodes and count among the avalanche diodes, i.e. they are optical sensors based on a silicon substrate. They form the basis for modern silicon photomultipliers (SiPM) and use the internal photoelectric effect to generate charge carriers and the avalanche effect for internal amplification. Similar to conventional photomultiplier tubes (PMT), they use the effects of impact ionization to generate secondary charge carriers. However, they get by with a significantly lower supply voltage and reach limit frequencies of up to the Gigahertz range. Their extremely high sensitivity enables the detection of weak light right down to individual photons. They are therefore also used for the detection of individual particles in high-energy physics. With regard to TCSPC, modern analog SiPM offer the possibility of inferring the photon rate directly from the voltage output. Read also: SPADs and HPDs.
bin size jitter, FWHM, RMS, quantization error
In time-to-digital converters, the bin size is the unit of quantization for time measurements. In our TDCs other jitter sources are smaller than the quantization error. Therefore the measurement error for short intervals is dominated by the bin size in our devices. Under these circumstances, the maximum measurement error is close to half a bin. The rooted mean square (RMS) error is about 0.8 bins and the full width half maximum error is about 2 bins.
Bathymetric lidar technology can be used in both shallow coastal waters and deep oceans to record the topography of the seafloor. The resulting point clouds can be used to create nautical charts, plan shipping routes, explore oil and gas deposits, and collect environmentally relevant information about the seafloor.
The term bathymetry refers to the surveying of the topographic shape of seabeds and water beds. Whereas in the past, the creation of bathymetric maps relied exclusively on surveys using handheld lead solders or depth sounders, nowadays LIDAR systems make it possible to create precise 3D images underwater much more efficiently. Due to the strong refraction of the water, the laser beam is strongly scattered during underwater propagation, which affects image quality. When using simple LIDAR sensor technology, such measurements are limited to waters with shallow to medium water depth and low turbidity. Accurate calibration of the lidar sensor and GPS receivers can help minimize inaccuracies due to waves and reflections.
However, there are also several techniques that can be used to minimize this interference, so that such measurements can even be made from satellites:
- Atmospheric correction: Some bathymetric lidar sensors use a technique called "atmospheric correction". This involves correcting for the reflection of laser light off air molecules in the atmosphere to obtain accurate range measurements.
- Multi-frequency Lidar: some lidar sensors use multiple laser frequencies to minimize the influence of waves and reflections on the water surface. By using multiple laser frequencies, wave reflections can be identified and filtered out to obtain more accurate measurements.
- The use of special filters: there are special filters that can be applied to the measurement data to minimize interference from waves and reflections. For example, statistical filters can be used to detect and remove outliers in the measurement data.
By combining these techniques (and more), bathymetric lidar sensors can produce accurate point clouds of the seafloor even when waves and reflections are present on the water surface.
cold target recoil-ion momentum spectroscopy, corresponding experimental setups are often called reaction microscopes, as well
Cold target recoil-ion momentum spectroscopy is a momentum imaging technique used to measure the complete fragmentation of an atomic or molecular few-body system. All charged fragments from an atomic, molecular, or surface reaction are projected onto large area position- and time-sensitive detectors. By measuring the individual particles’ times-of-flight and positions of impact on the detector, their 3D- momentum vectors are deduced. COLTRIMS measurements are coincidence measurements as many final-state fragments of single molecules or atoms are detected. Typical setups include a supersonic gas jet (i.e. molecular beam) as a target for the investigations and multi-hit capable MCP detectors with delay line position-readout for single particle detection.
triggered measurements, common-stop
In a common-start setup, time intervals are measured relative to a trigger signal on the "start"-input that is arriving before the pulses shall be measured. In such a scenario, the gate signal specifies the start time of the time measurement while the individual channel inputs end the time period.
triggered measurements, common-start
In a common-stop setup, time intervals are measured relative to a trigger signal that is arriving after the pulses that shall be measured. In such a configuration, the individual channel inputs deliver the start signal and the gate signal stops the measurement.
constant fraction discriminator
When measuring the arrival time of pulses with a fixed threshold the time measured exhibits a measurement error that is a function of the pulse amplitude. For setups where pulses have varying amplitudes but a constant rise time, a constant fraction discriminator (CFD) can reduce this error. Measuring a signal at two or three fixed thresholds with a high-resolution TDC can achieve the same quality of time walk correction as a CFD.
cycle to cycle jitter
short-term jitter, C2C jitter
Cycle-to-cycle jitter is a measure for the uncertainty in the interval between any two adjacent clock periods. In many TDC products, this is a major source of measurement error. For cronologic products, the cycle-to-cycle jitter is much less than the bin size. Care must be taken when comparing jitter specifications as various characteristics of the clock cycle distribution can be specified. Common specifications are the one sigma interval or the 95% interval of the distribution.
Discriminators are circuits that are used to create a digital signal for time measurement from an analog input waveform. The simplest form is a threshold discriminator that compares the input with a fixed voltage. Commonly used are constant fraction discriminators that compare against a voltage proportional to the pulse height.
DAQ is the abbreviation for data acquisition. This is the process of sampling signals that measure real-world (analog) physical conditions and making them available to application software. In personal computers, this is accomplished by data acquisition cards such as cronologic ADCs and TDCs.
Dead time describes a time interval during which a measurement device is not capable to acquire new measurements because it is still busy processing the previous one. Our products are optimized to minimize dead time. Read out always happens in parallel to measurement without disturbing it.
The position-readout of MCPs via a delay-line detector (DLD) is today’s best choice in the case of single-particle detection. Delay line detectors have excellent signal-to-noise properties, depict superior imaging dynamics, and, in addition, have a high time resolution. Modern delay-line detectors are furthermore multiple-hit-capable. Our TDCs are perfect companions for the readout of these detectors.
A delay-line position readout is used to measure the position of impact of a particle on a (typically larger area) microchannel plate detector with a resolution of approx. 100µm. The electron cloud, which is emitted at the location of the particle impact on the detector on the back of an MCP-stack induces a signal in a wire. The signal travels along the wire towards the wire’s two ends. By measuring the arrival time difference of the induced signal at each end of the wire, the position of impact on the wire can be deduced. In order to cover a larger area, the detection wire (i.e. the delay-line) is wound around a detector body. 2D-position of impact information can be obtained by employing a set of two orthogonal windings.
fluorescence lifetime imaging microscopy, photoluminescence decay measurements
Fluorescence Lifetime Imaging Microscopy (FLIM) is a microscopy imaging technique where time-correlated single-photon counting (TCSPC) is performed on each pixel of the image. The sample is scanned by a high-frequency pulsed laser beam, single photons of the emitted fluorescence light are detected, and the arrival time of each photon in the laser pulse period is determined by the TCSPC system and recorded in a histogram.
Read more about FLIM in this detailed article.
Functional Near-Infrared Spectroscopy
Functional Near-Infrared Spectroscopy (fNIRS) is a non-invasive method for brain imaging. In time-domain (TD) fNIRS the time-of-flight distribution (DTOF) of scattered photons is detected by multichannel time-to-digital converters.
frequency acquisition, frequency detection
In measuring the frequency of a periodic electronic signal, the number of cycles of oscillation, or pulses per second are counted. When it comes to recovering the frequency of the data pattern in a very short time or only in a few cycles, fast TDCs can improve the traditional method.
FCS, fluorescence lifetime correlation spectroscopy (FLCS)
Fluorescence-correlation-spectroscopy is a highly sensitive, time-resolved optical measurement method that can be used to study the mobility of fluorescent particles and molecular interactions. The widely used measurement method is based on a confocal microscope and reveals interesting biochemical parameters. During measurement fluctuations in the fluorescence emission intensity over time are recorded, which are caused by individual fluorophores that pass through the detection volume. With FCS, the size or shape of particles, diffusion constants, concentrations, and bonds between different diffusing species can be determined.
A combination of the time-correlated single photon counting (TCSPC) with the above-mentioned classic fluorescence correlation spectroscopy is called fluorescence lifetime correlation spectroscopy (FLCS). With this method, the time-resolved detection of fluorescence is used to separate the contribution of different processes to the measurement signal. The time resolution is in the picosecond range, which means that high-performance TDCs or ADCs are the best choices for data acquisition for such applications.
You might also be interested in this article about FLIM.
Fluorophores are molecules that emit fluorescence photons when excited from a light source. They can be utilized to visualize specific regions in cells using a fluorescence microscope.
In order to decrease the amount of data transmitted to the PC, some of our products include independent gating units that allow suppressing measurements during a time interval relative to the main trigger or a separate input signal.
hybrid detector, hybrid PMT, HPD, hybrid photomultiplier tube
A hybrid photo detector is a device for detecting very small amounts of light. Due to the low fluctuation, hybrid photodetectors are able to precisely determine the number of photoelectrons initially generated, as long as the maximum recording capacity is not exceeded. These detectors combine the properties of photomultipliers and avalanche photodiodes and provide a narrow pulse height distribution. For measurements in the time domain, this single amplification step leads to a regular propagation time spread and thus to low timing jitter.
Incoming photons are detected by an HPD using a photocathode (e.g. made of gallium arsenide phosphide), which emits a photoelectron with the highest possible quantum yield. This is strongly accelerated within a photomultiplier tube by means of high voltage in a vacuum, so that it finally hits an avalanche diode (electron bombardment). As a result, numerous electrons are released in the APD, so that the original photoelectron is duplicated more than a thousand times. In this way, measurable signals are generated that can be used for data acquisition.
Hybrid detectors have significantly lower dead times compared to PMTs or SPADs. Due to their high quantum efficiency, their large area (compared to SPADs), and fast time resolution these extremely light-sensitive detectors are commonly used in fluorescence lifetime microscopy and fluorescence correlation spectroscopy.
impulse response function
IRF, delta-distribution, Dirac delta function, unit impulse function
Impulse response analysis is an important aspect of digital signal processing with regard to the characterization of dynamic systems, such as measurement setups. The impulse response function (IRF) describes the reaction of the dynamic system to an external change. In digital measurement technology, this characterizes the deviation of the output signal for the case that an extremely short impulse is given to the input, whereby the impulse response describes the reaction of the system as a function of time. The so-called „unit impulse function“ has zero width, infinite height and an integral (area) of one. Since it is impossible in practice to generate such a perfect impulse as input for measuring the impulse response, the shortest possible impulse is used to approximate the ideal impulse to determine the impulse response. It is important that the impulse is short enough compared to the measured impulse response so that the result is close to the true impulse response and thus still provides a usable result for assessing a measurement setup.
intensified charge-coupled device
An intensified charge-coupled device is a very sensitive image sensor consisting of a charge-coupled device (CCD) to which a micro-channel plate is coupled through fiber optics to increase sensitivity. Due to the resulting amplification of the signal, they are optimal for low-light applications.
LiDAR, and LADAR, "light detection and ranging", "laser imaging, detection, and ranging", "3-D laser scanning, Lidar mapping"
Light Detection And Ranging is a method where the round-trip time of a laser reflection is measured using a time-to-digital converter (TDC). It is used 3-D laser scanning both airborne and stationary, for computer vision especially in autonomous vehicles and meteorological measurements.
Please also read our detailed article on this topic.
low count rate detection
particle detection, radiation detection, neutron detection, Geiger–Müller counter, scintillation counter, scintillation tracker, scintillation detector
Using single ion counting, low levels of radiation can be detected and characterized. In the area of radiation safety and non-proliferation small amounts of unknown nuclear material can be detected and identified using its spectra signature. Examples are special nuclear material (SNM) and shielded highly enriched uranium (HEU).
Matrix-assisted laser desorption/ionization
Matrix-Assisted Laser Desorption and Ionization is an ionization technique that can be used on large molecules with minimal fragmentation. This technology allows building time-of-flight (TOF) mass spectrometers for these molecules.
MCP microchannel plate detection, microchannel plate imaging, mcp imaging
Microchannel plate detectors (MCP) detect electrons, ions, or high-energy photons. They can be viewed as a further development of simple channeltrons (CEMs) and consist of a plate-shaped array of glass capillaries (between 10μm and 100μm inside diameter), which are provided with a semiconductor material on the inside. This layer on the capillary walls has electron-emitting properties, whereby the lead glass ensures a high electrical resistance between the capillaries. Each of the capillaries acts as an electron multiplier during detection: an accelerating voltage is applied between the two metalized plate sides and the capillary is arranged slightly tilted relative to the plate axis, so that incident electrons are certain to hit the wall of the respective capillary several times and generate secondary electrons again and again. These can then be recorded as measurable pulses with the help of fast TDCs or ADCs. Microchannel plates work with particularly low noise and, thanks to the matrix arrangement, also provide spatial information if required. This is beneficial for low-light imaging applications such as FLIM. Such multichannel plates are therefore also referred to as pixelated MCPs. MCP configurations with double or Z-stack MCP detectors are available for better resolution.
The following video shows an MCP detector receiving particles in a MALDI-TOF measurement:
multi-channel detector scaler, MCS, multi-hit TDC, multi-hit converter
A multi-channel scaler (MCS) is a pulse counting instrument that records the number of events that occur during a specified time interval and provides a time-histogram of counts versus time. MCS are commonly used in single-photon counting applications. All cronologic time measurement products can be used as multi-channel scalers.
Multi-Carrier Reflectometry (MCR) is a technique used to measure the reflectance of a surface or material respectively transmission lines.
It works by sending a multi-carrier signal and measuring the reflection that is returned. Such a type of digital signal is composed of several individual carrier signals that are transmitted simultaneously on different frequency bands. The carriers are modulated with data and combined to form the multi-carrier signal, which can then be transmitted. One of the main benefits of multi-carrier signals is that they can support high data rates and can be more resistant to interference and noise than single-carrier signals.
The reflection can be used to determine the properties of the surface respectively material, such as its reflectivity, roughness, and dielectric constant. MCR is used in a variety of applications, including material characterization, quality control, and surface analysis. It is a useful tool for understanding the physical properties of surfaces respectively materials and can provide detailed information about their characteristics.
Multi-Carrier Time Domain Reflectometry
Multi-Carrier Time Domain Reflectometry (MCTDR) is a technique for measuring the electrical characteristics of a transmission line or cable. MCTDR is a variant of multi-carrier reflectometry (MCR) in which multi-carrier signals are transmitted over the line and the reflections that return to the transmitter are measured, thus providing complete control over the spectrum of the injected signal. The reflections can be used to determine the characteristics of the transmission line, such as its impedance, attenuation, and phase shift.
In this approach to TDR measurements, the test signal is modulated as the sum of a finite number of sinusoidal oscillations and offers the advantage that the controlled spectrum of the injected signal can respond to electromagnetic compatibility (EMC) constraints. It offers the possibility to flexibly adjust the spectrum of the transmitted signal and modulate it in such a way as to allow circumvention of system-related limitations of online diagnosis by making it correspond to a specific spectral range. In this way, it is possible to avoid transmitting in a frequency band that interferes with the spectrum of the system. MCTDR is used in a variety of applications, including cable testing, fault location, and broadband transmission. It is a powerful tool for maintaining and troubleshooting transmission systems and can provide detailed information about the condition of a transmission line. MCTDR is one of the basic measurement methods in EWIS diagnostics since it can be used to detect hard faults such as short circuits and interruptions, often also intermittent defects and transient faults rather fast.
Nuclear Instrumentation Module standard
The NIM standard, originally an acronym for Nuclear Instrumentation Module, was developed in nuclear and high-energy physics in 1964. The included standards define mechanical and electrical specifications for modular systems with bus connections.
Optical Coherence Tomography
Optical coherence tomography is a high-resolution imaging system. It obtains 2- and 3-dimensional images from scattering materials (e.g. biological tissue). As a non-invasive diagnostic instrument, it is mostly used for ophthalmological examination of the retina. In this application, analog signals are sampled with ADCs so that the resulting digital pattern represents the analog signal as a function of the change in wavelength of the light source.
optical time-domain reflectometry
In optical fiber communications, the losses in optical fibers can be measured with optical time domain reflectometers. The measuring method works similar to radar but works with very low light levels and helps to localize poor fiber splices or faulty optical components.
In Optical Time Domain Reflectometry a fast light pulse is injected into the measured system (for example a fiber optic line). OTDR measurements are similar to TDR measurements, but are based on emitting a series of light pulses, e.g. by means of a laser. Here, the time of the reflections is determined from the reflection loss by measuring from the same end of the fiber how much light passes over the Rayleigh backscatter or is being reflected from individual locations along the fiber. OTDR measurement technology provides a snapshot of the entire connectivity of fiber optic networks, including all link points, splices, and fiber sections.
With help of a fast ADCs or TDCs the time parameters of the reflections and scatterings are measured in order to determine the location of the fault.
Please also read our detailed article on this topic.
photoactivated localization microscopy, PALM imaging, Single-molecule imaging, Single-molecule localization microscopy, SMLM, single-molecule microscopy
Photoactivated Localization Microscopy (PALM) is a super-resolution imaging technique that achieves nanometre-scale resolution by exploiting the properties of photoactivatable fluorophores to reveal spatial details of tightly packed molecules. This method enables the detection of individual molecules such as proteins in a cellular context. The method offers a high level of detail when depicting 3D structures in cell bodies and works like this:
Exposing fluorophores to low-power activating lasers of a certain wavelength leads to a change in their emission spectra. This conversion is implemented stochastically so that only a few fluorophores will turn into their active state. The stochastic excitation of the fluorophore ensures that each fluorescence point comes from a single fluorophore. A high-power laser beam briefly exposes these activated molecules, after which they are immediately returned to their inactive state (e.g. by photobleaching). This process is then repeated over thousands of images and the frames are merged into a super-resolution image.
single-photon detectors, SPD, detection of individual photons, photosensors, multi-pixel photon counter
See also: TCSPC. In single-photon counting, a single-photon detector (SPD) emits an electric pulse every time a photon is detected so that individual photons can be counted. Photon counting is used in telecommunication, biophysics imaging (e.g. FLIM), quantum optics and high-resolution (single-pixel) LIDAR, OTDR (optical time-domain reflectometry) and Quantum Key Distribution (QKD).
PCI eXtensions for Instrumentation
PCI eXtensions for Instrumentation is a bus system for measurement and automation technology. It is based on the older xPCI bus technology but uses the point-to-point PCI express standard for communication. Our standard PCIe products allow customers to build systems that deliver the same performance as a PXI setup at a fraction of the cost.
Classic photomultiplier tubes (PMT) work in the ultraviolet, visible, and near-infrared range of the electromagnetic spectrum. These are electron tubes that pick up weak light signals (up to individual photons) and amplify them to such an extent that free electrons produce more free electrons of lower energy, whereby the weak input signals are converted into measurable currents. They typically consist of a photocathode and a downstream secondary electron multiplier (SEM) in an evacuated glass bulb. PMTs can have dead times of tens of ns. A further development of the PMT, the hybrid photodetector, combines this with avalanche photodiodes.
A point cloud is a collection of three-dimensional coordinate points that represent the surface of a real or virtual object or, in other words a network of georeferenced data points. Each point in the cloud represents the position of a surface point in 3D space, and is typically represented by a set of x, y, and z coordinates. It can be created by various methods such as 3D scanning, structured light scanning, laser scanning, photogrammetry or even simulation.
A point cloud usually does not contain any other information such as colors or textures, but consists only of a collection of points with their coordinates. However, the point cloud can serve as a basis for further processing steps such as 3D modeling or metrology. Mostly point clouds are used to create 3D models of objects or environments, and can be visualized using specialized software. Point clouds are used in many application areas, such as 3D computer vision, architecture, engineering, surveying, robotics or virtual reality.
For example, such a three-dimensional point cloud might be the result of LIDAR measurements, where a spatial assignment is made for each point in the vector space by means of a big data analysis. The cloud of data points is described by the points it contains, each of which is captured by its spatial coordinates. This approach enables the representation of a surprisingly accurate 3D model of reality. In this context, the point density is an essential factor for the detection of objects and the possible resolution the in the field of visualization.
Quantum key distribution
The quantum key distribution enables tap-proof encryption of data. For this purpose, the quantum properties of light are used to transmit encrypted data. Single-photon sources (SPS) are used for optimal performance. Our fast TDCs can be used in single-photon counting receiver modules that convert single-photon detection events into streams of timestamps.
Read more about quantum research in this article.
quadrupol mass analyzers
QMS, QTOF, TQMS
Quadrupole mass analyzers can be used as an upstream mass filter in TOF mass spectrometry (QTOF). With their help, all ions can be eliminated for the detection of certain substances that are not within the desired range from mass to charge. A quadrupole mass analyzer consists of the arrangement of two oppositely identical electrical or magnetic dipoles with a fixed distance over their entire length. In mass filter analysis with an electric quadrupole, the inertia of the introduced particles is used for selection: the light particles are destabilized in one of the levels and the heavy particles in the other level by means of an applied alternating voltage. Quadrupoles can also be used to focus the ion beam in a mass spectrometer, e.g. to align the ions with a collision cell and to record the fragments produced there by means of time-of-flight measurement.
Note: There are also mass spectrometers that use quadrupoles and similar arrangements to record an entire mass spectrum (QMS). In terms of their detection capabilities, these do not come close to the performance of the TOF-MS, because in these devices the stability range is scanned over the entire m / Q range and a new measurement is carried out at every step. As a result, such measurements require a significantly higher investment of time. Triple quadrupole mass spectrometers (TQMS) should also be mentioned at this point. These are tandem mass spectrometers, which consist of two quadrupole mass analyzers connected in series and are separated by a (non-mass-resolving) high-frequency quadrupole, which serves as a cell for the collision-induced dissociation. The aim is to increase the sensitivity of the measurement. However, this coupling does not achieve the performance of a TOF measurement either.
A reciprocal counter measures a frequency by measuring the time between a certain number of edges of a clock signal. This is opposed to the approach of a simple counter that counts the number of signal edges in a certain time interval. All of our TDCs can be used as reciprocal counters with very high precision. To measure frequencies that are higher than the maximum count rate of a given TDC an external prescaler is required.
A reflectron is used to improve the mass resolution in a mass spectrometer. It is used to reverse the direction of the ions by creating an electric field with a gradient. The field decelerates the ions and then accelerates them again in the opposite direction. This reduces the influence of their kinetic energy distribution on the flight time, because the ions with higher kinetic energy penetrate deeper into the electrical field of the reflector and cover a correspondingly longer distance, which largely compensates for the flight time differences.
The background to this feature is, that it is technically not exactly easy to ensure in a mass spectrometer that all ions really absorb the same amount of energy. During the measurement, the sample is in a gaseous state, which means that the energy distribution of the gas particles within the ion source follows a Boltzmann distribution. During the acceleration phase, different parts of the sample are therefore exposed to the electric field to a greater or lesser extent than others. As a result, they do not consume the same amount of energy, which would, however, be a prerequisite for correct measurements. Therefore a deviation occurs and particles with the same mass-to-charge ratio are nevertheless accelerated to different speeds. These ions have different kinetic energies and this energy dispersion acts as a blurring in the mass spectrum. The energy dispersion can be minimized with the help of a reflector.
See graphic below:
single photon avalanche diodes
SPAD, Geiger-mode avalanche photodiode, GmAPD
Single photon avalanche diodes (SPAD) are solid-state photodetectors and belong to the same family as photodiodes and avalanche photodiodes (APDs) but require no vacuum. While APDs show their strengths in the undistorted amplification of low-intensity optical signals, the behavior of SPADs is more closely related to the basic diode behavior. SPADS enable the direct counting of pulses and thus provide an indication of the optical intensity of the input signal, while the pulses can simultaneously trigger timing circuits to enable precise measurements of the time of arrival. These sensors are used in particular in time-of-flight 3D imaging, LIDAR technology, PET scanning, TCSPC, fluorescence lifetime microscopy and optical communication, especially in quantum key distribution. SPADs are particularly useful for single photon detection, e.g. using SPAD arrays a full FLIM image can be captured as even single photons produce a clear output signal which can be detected. SPADs have a low dead time (less than 1 ns) and consequently a high count rate, with a delay spread comparable to MCPs. A distinctive feature of SPADs is their dark noise. Since dark noise increases with area, this effect is an important criterion when increasing the light-sensitive area in SPADs.
The name Geiger-mode avalanche photodiode (GmAPD) refers to the fact that the diode is operated slightly above the breakdown threshold voltage. This leads to the fact that already a single electron-hole pair (generated by absorption of a photon or by a thermal fluctuation) can trigger a strong avalanche.
Hint: You might also be interested in HPDs.
single molecule fluorescence spectroscopy
SMD, single molecule detection, single-particle tracking, SPT, PALM microscopy, single-molecule imaging, single-molecule localization microscopy, SMLM
Single molecule fluorescence spectroscopy is a method of physical chemistry in which individual molecules can be made visible. Thus the dynamics and interactions in cellular systems can be examined. The technique has developed rapidly in recent years, especially in the area of high-throughput single molecule detection. In biomolecular analysis, the method enables the identification of subpopulations and the localization of molecules with sub-wavelength precision. The technology is used in biological, clinical and medical research to follow the movement of individual molecules in living cells, e.g. for ultra-sensitive and specific DNA sequencing or for the detection of diseases.
During the process, the sample is brought under a special light microscope, which is optimized for the extremely small detection volume, and then excited by means of a laser. The photons emitted during the resulting fluorescence triggered can be tracked over longer periods of times with the aid of a microscope (single-particle tracking, SPT) or may also be put underneath a time-correlating single photon measurement.
silicon photomultipliers (SiPM)
Silicon photomultipliers (SiPM) are single-photon sensitive semiconductor devices, more specifically arrays of hundreds to tens of thousands of integrated SPADs implemented on a common silicon substrate, each capable of individually and independently detecting photons.
All microcells are read in parallel. This makes it possible to generate signals in a dynamic range from a single photon to 1000 photons for a device with an area of only one square millimeter.
Compared to conventional PMTs, there is a low or even negligible additional noise factor. In addition, the bias voltages are 10 to 100 times lower, which simplifies the electronics. In the red to near-infrared they have a significantly higher quantum efficiency than available PMTs and a significantly larger dynamic range when a large number of SPADs are placed together. This enables faster imaging rates or a higher signal-to-noise ratio.
Please note: Unlike PMTs, SiPM may require sub-ambient cooling and may be difficult to obtain large active areas as the dark numbers per area are higher than PMTs.
Superconducting nanowire single-photon detectors
(SNSPD or SSPD)
SNSPD are considered the fastest single-photon detectors (SPD) for photon counting and are considered as key technology for quantum optics and optical quantum technologies.
Superconducting nanowire single photon detectors are based on the principle of superconducting detection. A superconducting material conducts electric current without any resistance when cooled below a critical temperature called the transition temperature. When a photon hits such a detector, it is absorbed, causing a pair of electrons called a Cooper pair to form. The formation of the Cooper pair causes a decrease in the electrical resistance of the superconducting material, which is registered as a signal.
Superconducting nanowire single photon detectors offer high sensitivity and high temporal resolution with very high count rates, very short dead times, and very low temporal jitter compared to other single-photon detectors. They can detect single photons at very low intensity, making them ideal for quantum communications, quantum cryptography and quantum computing. Because they are based on superconducting technology, they also have a very low background rate, which means they are very accurate and do not cause false alarms.
However, using superconducting nanowire single photon detectors also has disadvantages. One of the biggest drawbacks is that they usually need to be cooled to very low temperatures, usually below 4 Kelvin (-269°C). This requires special cooling equipment, which can be expensive and impractical. In addition, they have a limited detection area and are therefore not suitable for covering large areas.
Overall, superconducting nanowire single photon detectors offer high sensitivity and high temporal resolution, but may not be suitable for all applications due to their technical limitations.
Single Photon LIDAR
Single photon LIDAR offers particularly fast data acquisition and a particularly high data density, because this technique detects multiple laser pulses simultaneously and analyzes them separately. The Single Photon Lidar (SPL) technique uses collimated laser radiation in the visible green region of the spectrum (λ=532 nm). The collimation of the laser pulse is achieved by using a diffractive optical element (DOE) to split the laser into several partial beams, called "beamlets". In this way, the density of the measurement points is significantly increased. In contrast to GmLidar, not the entire FOW of the receiver is illuminated in full, but each beamlet is aligned in its spatial direction in such a way that it hits a single-photon-sensitive detector array assigned to it on the detector side, the so-called "sub-array". Each individual sub-array consists of numerous light-sensitive detector elements and virtually splits the FOW into sub-areas that can be included in the analysis in parallel. In this way, the light-sensitive sub-arrays are efficiently illuminated and optical crosstalk is avoided. Provided that the dynamic range is properly adjusted, the strength of the output signal from the sub-arrays is linear with respect to the optical power. In this way, each laser beamlet can deliver multiple echoes, the analysis of which also makes it possible to pass through vegetation, for example. Compared to conventional LIDAR, SPL provides higher area performance at comparable point cloud densities, although the height accuracy for non-planar surfaces is somewhat lower than with full-waveform LIDAR. Single-photon LIDAR is more sensitive to multiple reflections than Geiger-mode LIDAR. As it currently stands, SPL does not achieve the precision of full-waveform LIDAR.
The wavelength used in SPL makes it possible to perform bathymetric measurements and combine them with topographic surveys.
A typical use case for SPL would be the detection of objects under foliage in a forest from above. In this case, individual beamlets might detect treetops, others might hit and be reflected by some branches along the way, and other beamlets might hit the ground and provide corresponding data.
Time Correlated Single Photon Counting, time domain FLIM, tdFLIM
In Time-correlated single-photon counting (TCSPC) fluorescence decays are measured over the time axis. The method is an essential part of fluorescence lifetime imaging microscopy (FLIM). Time-Correlated Single Photon Counting is considered a particularly gentle measurement technique because the light pulses required for sample excitation have low pulse energy. This is possible because only a single photon is processed at a time. TCSPC is based on the detection of these individual photons and the measurement of their arrival times in relation to a reference signal, which is usually the time of emission of the laser pulse that was used to excite the sample. This laser pulse occurs with a high repetition rate so that a sufficiently high number of individual photons can be determined for the resulting measurement of the fluorescence lifetime.
Most of our ADC and TDC products are equipped with this feature which is a great help to control your experimental setup. The TiGer can be used to output periodic Timing patterns, delayed copies of other signals, or random triggers among other use cases.
trigger blocks, mapping
In most cronologic products, any digital input can be used to trigger any triggerable circuit. The mapping is performed by the configurable trigger matrix. Inputs can be input connectors, TiGer pattern generators, software triggers, and others. Triggerable circuits can be input gates, TiGer pattern generators, auxiliary ADC measurements among others.
Transient recorders are oscilloscopes that are designed to measure waveforms with very high bandwidth. Unlike equivalent time sampling scopes a transient recorder acquires the measurement in a single shot. The signal does not need to be repetitive. For digital data acquisition products, the terms ADC, digitizer, and transient recorder are mostly used interchangeably.
TOF- & MASS- spectroscopy / spectrometry detectors, TOFMS, ion-counting, ionization spectroscopy
In time-of-flight mass spectrometers ions are accelerated in an electric field. The time it takes for the ion to reach a detector is used to determine the mass-to-charge ratio of the ion. With a constant-fraction-discriminator (CFD) and time-to-digital converters, the flight time of the ion can be easily be measured with high precision. In setups where a high number of ions of the same mass is created, an ADC digitizer can be used instead to also obtain information on the pulse height and thus on the number of ions in each measured pulse.
Read more about TOF-MS in this article.
All of our ADCs feature onboard zero suppression. The idea of this feature is, that only data that meet specifications predefined by the user are transmitted. This reduces PCIe busload in order to make maximum use of the available readout bandwidth. When set up correctly, only relevant pulses (above a certain threshold level) are detected, so that the amount of data that needs to be copied and analyzed is reduced drastically.