Photon counting at certain wavelengths in the UV, visible and near-IR range is one of the key technologies in today's fast-growing analytical instrumentation, diagnostics, and scientific applications space.
These Single Photon Counting Modules (SPCMs) are self-contained modules that offer market-leading photon counting performance in parameters like high Photon Detection Efficiency (PDE), low after pulsing, highest uniformity over active area, high linear dynamic range, and low dark counts. This series of single photon counting modules are designed and built to be fully RoHS-compliant.
The SPCMs we offer were the first APD-operated photon counting devices on the market. They use a unique APD that was developed specifically to be operated in so-called "Geiger-mode", which means operated above breakdown voltage, so that a single incoming photon triggers an avalanche of electrons already large enough to be detected and counted as an electronic pulse. The SPCM uses a unique silicon avalanche photodiode (SliKTM) with a circular active area intended for peak photon detection efficiency. The photodiode is both thermoelectrically-cooled and temperature-controlled, ensuring stabilised performance despite ambient temperature changes.Send Enquiry
An Avalanche Photodiode (APD) provides higher sensitivity than a standard photodiode. It is ideal for extreme low-level light (LLL) detection and photon counting. Offered in Silicon or InGaAs materials, these devices provide detectivity from 400 nm - 1100 nm. Multiple configurations are available to provide a wide range of sensitivity and speed options.
The use of APDs instead of PIN Photodetectors will result in improved sensitivity in many applications. In general, APDs are useful in applications where the noise of the amplifier is high — i.e., much higher than the noise in the PIN Photodetector. Thus, although an APD is always noisier than the equivalent PIN, improved signal-to-noise can be achieved in the system for APD gains up to the point where the noise of the APD is comparable to that of the amplifier.
For example, when the system bandwidth is high, the amplifier noise is high, and an APD is likely to be useful. On the other hand, in very low bandwidth systems, the noise of the amplifier is likely to be very low, in which case, the APD may not be the best choice. In applications where the background optical power falling on the detector is very high, such as operation of the detector in daylight conditions with little or no filtering, an APD may not be useful, except perhaps at low gain, since the multiplied noise of the background illumination will be very high and may exceed that of the amplifier.
Products offered include:
Excelitas utilises Silicon and InGaAs materials for their photodiodes to provide detection from 220nm to 1700nm. These devices are offered in a variety of sizes to meet customer sensitivity and speed requirements.
Phototransistors are examples of photodiode-amplifier combinations integrated within a single silicon chip.
Photodiodes are unique among light detectors in that when illuminated, they generate an output which is proportional to light level. They are solid state light detector that consists of a shallow diffused P-N junction with connections provided to the outside world. When the top surface is illuminated, photons of light penetrate into the silicon to a depth determined by the photon energy and are absorbed by the silicon generating electron-hole pairs. The electron-hole pairs are free to diffuse (or wander) throughout the bulk of the photodiode until they recombine. The average time before recombination is the "minority carrier lifetime".
Phototransistors are solid state light detectors that possess internal gain. This makes them much more sensitive than photodiodes of comparably sized area. These devices can be used to provide either an analogue or digital output signal. The phototransistor can be viewed as a photodiode whose output photocurrent is fed into the base of a conventional small signal transistor. While not required for operation of the device as a Photodetector, a base connection is often provided allowing the designer the option of using base current to bias the transistor. The typical gain of a phototransistor can range from 100 to over 1500.
Warsash Scientific offer instrumentation for:
The analogue optical isolator (AOI) uses an optical link between input and output. The input element is an LED and the output element is a photoconductive cell or simply photocell. Together, the coupled pair acts as an electrically variable potentiometer. Since the output element of the AOI is a resistor, the voltage applied to this output resistor may be DC and/or AC and the magnitude may be as low as zero or as high as the maximum voltage rating. Because the input will control the magnitude of a complex waveform in a proportional manner, this type of isolator is an analogue control element. AOIs may be used in the ON-OFF mode but the fastest response time is in the millisecond range. A level sensitive Schmitt trigger is required between the AOI and logic gates when used in digital circuits.
Optoswitches are ideal for non-contact sensing applications. They consist in an emitter and a detector integrated in a plastic housing. The emitter is an IR LED while the detector is either a phototransistor or a photodarlington. These optoswitches are available either in transmissive or reflective configuration.
In its most basic form, a reflective optical switch (retro) consists of a housing which holds both a light source and a detector. Light from the lamp of LED radiates outward and is reflected back should an object be placed in front of the switch. The reflected light is sensed by the Photodetector whose output signal changes accordingly.
When the object to be sensed has a polished surface, such as aluminium foil or Mylar tape, often the best type of reflective switch to use is one which is designed to take advantage of the large amount of directly reflected light. This is done by mounting the emitter and detector such that their optical centres lie along the legs of an isosceles triangle such that the angle of the incidence of the emitter is equal to the angle of reflection.
When trying to sense matte objects (which do not have a highly polished surface, such as white paper), it is often possible to use a type of reflective switch optimised for sensing diffuse reflected light. Such devices have the emitter and detector mounted parallel to each other within the switch housing.Send Enquiry
The Photocell Light-Dependent Resistor can provide a very economical and technically superior solution for many applications where the presence or absence of light is sensed (digital operation) or where the intensity of light needs to be measured (analogue operation).
Semiconductor light detectors can be divided into two major categories: junction and bulk-effect devices. The bulk-effect photoconductors have no junction. The bulk resistivity decreases with increasing illumination, allowing more photocurrent to flow. This resistive characteristic gives bulk-effect photoconductors a unique quality: signal current from the detector can be varied over a wide range by adjusting the applied voltage.
To clearly make this distinction, we refer to photoconductors as photoconductive cells or, simply, "Photocells". Photocells are thin-film devices made by depositing a layer of a photoconductive material on a ceramic substrate.