Thorlabs' Free-Space Silicon Avalanche Photodetectors (APD) are designed to offer increased sensitivity and lower noise compared to standard PIN detectors, making them ideal for applications with low optical power levels. In addition to our standard APDs, versions featuring variable gain (i.e., M factor) and/or temperature compensation are offered.

It is not safe to use the detector to measure this pulsed laser emission, since the peak power of the pulses is >5 orders of magnitude higher than the detector's maximum peak optical input power.

These numbers can vary from model to model, but their order remains the same. The magnification of the objective lens is shown first and then the aperture (after a slash). We emphasize that we mean the numerical aperture (the angular aperture is not marked anywhere). The numerical and angular apertures are connected by a complicated mathematical formula.

In order to learn what this parameter means, take a look at the objective lens shell. It should say something like “100/1.25 oil 160/0.17”. It is interpreted as follows:

The detectors maintain high gain stability over the 10 °C to 40 °C temperature range by utilizing a temperature compensation circuit, which adjusts the ~150 V DC bias to ensure operation near the breakdown voltage.

Our APD130A2(/M) and APD130A(/M) temperature-compensated APDs feature integrated thermistors that adjust the bias voltage to compensate for the effect of temperature changes on the M factor. A comparison with our non-temperature-compensated APDs is provided in the graph to the right.

The orientation of the mechanical and electrical connections, combined with the compact design, ensures that these detectors can fit into tight spaces. Three 8-32 (M4) mounting holes, one on each edge of the housing, further ensure easy integration into complicated mechanical setups. The housing also provides compatibility with both our SM05- and SM1-Series Lens Tubes. An internally SM1-threaded cap is included.

Determining whether emission from a pulsed laser is compatible with a device or application can require referencing parameters that are not supplied by the laser's manufacturer. When this is the case, the necessary parameters can typically be calculated from the available information. Calculating peak pulse power, average power, pulse energy, and related parameters can be necessary to achieve desired outcomes including:

Our online store offers an ample selection of reliable microscopes for precise and comfortable studying the microscope slides. Explore the micro world with quality optical tools!

InGaAsphotodiode

The manufacturer reserves the right to make changes to the pricing, product range and specifications or discontinue products without prior notice.

Please note that Thorlabs also offers the APD431A fiber-coupled Si photodetector, which features an M12 x 0.15-threaded flange that is directly compatible with our M12 x 0.5-threaded fiber connector adapters. This compact and robust mechanism allows for easy fiber coupling with high reproducibility. The M12 x 0.5-threaded flange can be added to any of Thorlabs' Avalanche Photodetectors to provide robust fiber-coupling capabilities. Please contact Tech Support for more information.

These Free-Space Avalanche Photodetectors feature a variable gain that can be controlled by a knob on the right side of the housing. Like the APD130A detectors above, these devices feature an integrated thermistor that maintains an M factor stability of ±3% or better over 23 ± 5 °C by adjusting the bias voltage across the avalanche photodiode. Compared to the standard and temperature-controlled APDs above, the APD430A2 and APD430A detectors also offer a larger usable bandwidth of DC to 400 MHz. The APD410A2 and APD410A detectors offer a slightly smaller usable bandwidth (DC to 10 MHz), but with higher sensitivity. The APD440A2 and APD440A detectors offer high transimpedance gain with a lower max bandwidth of 100 kHz.

In addition to being temperature compensated, our variable-gain APD400 series detectors allow the reverse bias voltage across the diodes to be adjusted via a rotary knob on the side of the housing, which varies the M factor from 5 to 50 or 10 to 100.

Models for both the visible and near infrared range are available. The compact design of these detectors allows for easy OEM integration.

These Fiber Adapters can be used with many of our avalanche photodetectors above. Note that we do not recommend using fiber connector adapters alone to couple light onto the APD401A2(/M), APD430A2(/M), and APD430A(/M) avalanche photodetectors due to the small size of their sensors. To achieve high coupling efficiency, a fiber collimation package, focusing lens, and X-Y translator should be used. See the Fiber Coupling tab for details.

Pulsed laser radiation parameters are illustrated in Figure 1 and described in the table. For quick reference, a list of equations is provided below. The document available for download provides this information, as well as an introduction to pulsed laser emission, an overview of relationships among the different parameters, and guidance for applying the calculations.

The orientation of the mechanical and electrical connections, combined with the compact design, ensures that these detectors can fit into tight spaces. Three 8-32 (M4) mounting holes, one on each edge of the housing, further ensure easy integration into complicated mechanical setups. The housing also provides compatibility with both our SM05- and SM1-Series Lens Tubes. An internally SM1-threaded cap is included.

A complete list of all of our APDs can be found on the Selection Guide tab. Please note that our Single Photon Detectors are the only avalanche photodetectors suitable for single photon counting.

What is the numerical aperture of a microscope (objective lens)? That value says what resolution power a microscope will have while using a particular objective lens. The larger the numerical aperture, the tinier the details can be that a microscope can deliver sharply. Let’s take two objective lenses: 40/0.65 and 40/1.3. Both accessories feature equal magnification of 40x, but we will observe a sharper image while using an objective lens with a 1.3 aperture. We will be able to study even fine nuances of microstructures and more differences between closely placed elements of specimens. Roughly, a 40/0.65 objective lens delivers a blurrier image than a 40/1.3 objective lens. Note that the numerical aperture value is less significant at low magnifications. It should be taken into account only when choosing an objective lens with 40x magnification and higher.

Originally developed for the detection of the beat note signal between CW or pulsed lasers, Menlo Systems' Si Avalanche Photodetectors are ideally suited for applications requiring very high sensitivity for low-light input signals in the 200 - 1000 nm or 400 - 1000 nm range. The APD avalanche photodiode series can provide an extremely sensitive alternative to traditional PIN photodiodes. They are also fast enough for the characterization of, for example, pulsed solid-state lasers on the nanosecond time scale.

The FC/PC and FC/APC adapters are available in narrow or wide key versions; for details on narrow versus wide key connectors, please see our Intro to Fiber tutorial.

Our SM1-threaded fiber adapters are compatible with these detectors. The internally SM1-threaded adapters can be mated directly to the housing, and are available below. To use our externally SM1-threaded fiber adapters, an internally SM1-threaded lens tube will be required to mate the fiber adapter to the detector's housing. The externally SM05-threaded fiber adapters are not compatible with these detectors.

Fiber Coupling Note:A fiber coupling mechanism can be constructed for our free-space APDs using standard optomechanics. For fiber-coupled applications, we do not recommend using fiber connector adapters such as Thorlabs' S120-FC with the APD410A2(/M), APD430A2(/M), and APD430A detectors due to the small size of the sensors. High coupling losses and degradation of the frequency response may occur. To achieve high coupling efficiency, a fiber collimation package, focusing lens, and X-Y translator should be used. See the Fiber Coupling tab for details.

The units are especially recommended for applications such as metrology when homodyne or heterodyne optical beat signals of weak power have to be detected and amplified in a highly efficient way.

The S120-25 ferrule adapter is designed without a locking connector mechanism and accepts fiber patch cables with Ø2.5 mm ferrules for quick measurements with photodetectors or power sensors.

The FC/APC adapters have two dimples in the front surface that allow them to be tightened with the SPW909 or SPW801 spanner wrench. The dimples do not go all the way through the disk so that the adapter can be used in light-tight applications when paired with SM1 lens tubes.

Is it safe to use a detector with a specified maximum peak optical input power of 75 mW to measure the following pulsed laser emission?

In general, avalanche photodiodes use an internal gain mechanism to increase sensitivity. A high reverse bias voltage is applied to the diodes to create a strong electric field. When an incident photon generates an electron-hole pair, the electric field accelerates the electrons, leading to the production of secondary electrons by impact ionization. The resulting electron avalanche can produce a gain factor of several hundred times, described by a multiplication factor, M, that is a function of both the reverse bias voltage and temperature. In general, the M factor increases with lower temperatures and decreases with higher temperatures. Similarly, the M factor will increase when the reverse bias voltage is raised and decrease when the reverse bias voltage is lowered.

Please note that Thorlabs also offers the APD431A fiber-coupled Si photodetector, which features an M12 x 0.15-threaded flange that is directly compatible with our M12 x 0.5-threaded fiber connector adapters. This compact and robust mechanism allows for easy fiber coupling with high reproducibility. The M12 x 0.5-threaded flange can be added to any of Thorlabs' Avalanche Photodetectors to provide robust fiber-coupling capabilities. Please contact Tech Support for more information.

An objective lens is a part of the microscope optical system that forms an enlarged image. When buying an additional objective lens, users usually pay attention to its magnification power because it has a direct impact on the magnification of the optical tool. One more specification that should be considered when choosing this accessory is the numerical aperture of the microscope objective lens.

Thorlabs' APD130A2(/M) and APD130A(/M) Free-Space Avalanche Photodetectors feature an integrated thermistor that maintains an M factor stability of ±3% or better over 23 ± 5 °C by adjusting the bias voltage across the avalanche photodiode, supplying improved output stability in environments with temperature variations.

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Edmund Opticsphotodiode

A fiber coupling mechanism can be constructed for our free-space APDs using standard optomechanics. In fiber coupling applications, we recommend taking into account the divergence of light from the fiber tip to ensure that all of the signal is focused onto the detector active area. When using a standard fiber connector adapter with a detector with an active area smaller than Ø1 mm, high coupling losses and degradation of the frequency response may occur.

Thorlabs offers Menlo Systems' APD410 and APD210 Variable-Gain Avalanche Photodetectors, which offer high-speed responses up to 900 MHz or 1 GHz at 3 dB, respectively. Additionally, we offer spectral-flattening filters that are designed to improve the response uniformity of our silicon photodiodes and detectors; click here to learn more.

To achieve high coupling efficiency, a fiber collimation package, focusing lens, and X-Y translator should be used, as shown in the photo to the right. The avalanche photodetector is shown with a fiber collimator, lens tube collimator adapter, lens tube, and X-Y translation mount. An adapter inside the lens tube holds an aspheric lens (not visible) to focus the collimated light onto the active area of the detector. The X-Y translation mount corrects for any centering issues.

The LDS12B ±12 VDC Regulated Linear Power Supply is intended as a replacement for the supply included with our APD series of avalanche photodetectors sold on this page, except for the APD210 photodetector. The cord has three pins: one for ground, one for +12 V, and one for -12 V (see diagram to the right). A region-specific power cord is shipped with the unit based on your location. This power supply can also be used with the PDA series of amplified photodetectors, PDB series of balanced photodetectors, PMM series of photomultiplier modules, and the FSAC autocorrelator for femtosecond lasers.

Figure 1: Parameters used to describe pulsed laser emission are indicated in the plot (above) and described in the table (below). Pulse energy (E) is the shaded area under the pulse curve. Pulse energy is, equivalently, the area of the diagonally hashed region.