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Si Free-Space Amplified Photodetectors
PDA Series Detector with Ø1" Lens Tube Attached to a 30 mm Cage System
We offer a selection of Silicon (Si) Free-Space Amplified Photodetectors that are sensitive to light in the UV to the NIR wavelength range. Thorlabs' amplified photodetectors feature a built-in low-noise transimpedance amplifier (TIA) or a low-noise TIA followed by a voltage amplifier. Menlo Systems' FPD series amplified photodetectors have a built-in radio frequency (RF) or transimpedance amplifier. We offer fixed-gain versions that possess a fixed maximum bandwidth and total transimpedance gain, as well as switchable-gain versions with two or eight gain settings.
Thorlabs' photodetectors are designed to meet a range of requirements, with offerings that include the 380 MHz PDA015A with an impulse response of 1 ns, the high-sensitivity PDF10A with a noise equivalent power (NEP) of 1.4 fW/Hz1/2, and the switchable-gain PDA100A2 with eight switchable maximum gain (bandwidth) combinations from 1.51 kV/A (11 MHz) to 4.75 MV/A (3 kHz). The PDF10A with femtowatt sensitivity is a low-frequency device that should only be terminated into high impedance (Hi-Z) loads, while all other of our silicon amplified photodetectors are capable of driving loads from 50 Ω to Hi-Z.
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The PDA10A2 with the Included ±12 V Power Supply. Replacement power supplies are sold below.
Every detector has internal SM05 (0.535"-40) threading and external SM1 (1.035"-40) threading. Except for some select detectors, each unit's housing features 8-32 tapped holes (M4 for -EC and /M models). The PDA10A2, PDA36A2, and PDA100A2 feature a new housing with universal taps that accept both 8-32 and M4. For more information about the location of these mounting points and mounting these units, please see the Housing Features and Mounting Options tabs.
Menlo Systems' FPD series detectors are easy-to-use photodiode packages with an integrated high-gain, low-noise RF (FPD310-FS-VIS) or transimpedance (FPD510-FS-VIS and FPD610-FS-VIS) amplifier. The FPD310-FS-VIS is ideal for experiments requiring high bandwidths and extremely short rise times (<1 ns). This detector has a switchable gain with two steps, 0 and 20 dB. The FPD510-FS-VIS and FPD610-FS-VIS have a fixed gain and are optimized for the highest signal-to-noise ratio when detecting low-level optical beat signals at frequencies up to 250 MHz and 600 MHz, respectively. The FPD510-FS-VIS has a rise time of 2 ns, while the FPD610-FS-VIS has a 1 ns rise time. The 3 dB bandwidth of these DC-coupled devices is 200 MHz for the FPD510-FS-VIS and 500 MHz for the FPD610-FS-VIS. The compact design of the FPD detectors allows for easy OEM integration. The housing of each Menlo detector features one M4 tapped hole for post mounting. For more information about the housing, please see the Housing Features tab. For versions of these detectors with FC/PC inputs, see Si Fiber-Coupled Amplified Detectors.
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Menlo Systems’ Detectors Include a Location-Specific ±12 V Power Supply
Menlo's FPD510-FS-VIS, FPD610-FS-VIS, and FPD310-FS-VIS include a low-noise power supply.
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Top of the housing on our PDA and PDF detector housings. The Power In connector, Output BNC connector, and power indicator LED are located at the top of the housing. The PDA015A detector is shown.
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The housings of Thorlabs' detectors feature internal SM05 and external SM1 threads. An SM1T1 SM1 Adapter with internal threads is included with each amplified photodetector, and an SM1RR Retaining Ring is included with the PDA015A, PDA10A2, PDA36A2, and PDA100A2.
Housing Features of the Amplified Si Photodetectors
PDA and PDF Detectors
PDA and PDF Series Mounting Options
The PDA series of amplified photodetectors are compatible with our entire line of lens tubes, TR series posts, and cage mounting systems. Because of the wide range of mounting options, the best method for mounting the housing in a given optical setup is not always obvious. The pictures and text in this tab will discuss some of the common mounting solutions. As always, our technical support staff is available for individual consultation.
TR Series Post (Ø1/2" Posts) System
The PDA housing can be mounted vertically or horizontally on a TR Series Post using the threaded holes for 8-32 (M4 on metric versions). Select PDA housings feature universally threaded holes for both 8-32 and M4 threads.
Lens Tube System
Each PDA housing includes a detachable Ø1" Optic Mount (SM1T1) that allows for Ø1" (Ø25.4 mm) optical components, such as optical filters and lenses, to be mounted along the axis perpendicular to the center of the photosensitive region. The maximum thickness of an optic that can be mounted in the SM1T1 is 0.1" (2.8 mm). For thicker Ø1" (Ø25.4 mm) optics or for any thickness of Ø0.5" (Ø12.7 mm) optics, remove the SM1T1 from the front of the detector and place (must be purchased separately) an SM1 or SM05 series lens tube, respectively, on the front of the detector.
The SM1 and SM05 threadings on the PDA photodetector housing make it compatible with our SM lens tube system and accessories. Two particularly useful accessories include the SM-threaded irises and the SM-compatible IR and visible alignment tools. Also available are fiber optic adapters for use with connectorized fibers.
The simplest method for attaching the PDA photodetector housing to a cage plate is to remove the SM1T1 that is attached to the front of the PDA and use the external SM1 threads. A cage plate, such as the CP02 30 mm cage plate, can be directly attached to the SM1 threads. Then the retaining ring, included with the SM1T1, can be threaded using a spanner wrench into the CP02 to ensure the cage plate is tightened to the desired location and square with the photodetector housing.
This method for attaching the PDA photodetector housing to a cage plate does not allow much freedom in determining the orientation of the photodetector; however, it has the benefit of not needing an adapter piece, and it allows the diode to be as close as possible to the cage plate, which can be important in setups where the light is divergent. As a side note, Thorlabs sells the SM05PD and SM1PD series of photodiodes that can be threaded into a cage plate so that the diode is flush with the front surface of the cage plate; however, the photodiode is unbiased.
For more freedom in choosing the orientation of the PDA photodetector housing when attaching it, an SM1T2 lens tube coupler can be purchased. In this configuration the SM1T1 is left on the detector and the SM1T2 is threaded into it. The exposed external SM1 threading is now deep enough to secure the detector to a CP02 cage plate in any orientation and lock it into place using one of the two locking rings on the ST1T2.
Although not pictured here, the PDA photodetector housing can be connected to a 16 mm cage system by purchasing an SM05T2. It can be used to connect the PDA photodetector housing to an SP02 cage plate.
The image below shows a Michelson Interferometer built entirely from parts available from Thorlabs. This application demonstrates the ease with which an optical system can be constructed using our lens tube, TR series post, and cage systems.
The table below contains a part list for the Michelson Interferometer for use in the visible range. Follow the links to the pages for more information about the individual parts.
PDA and PDF Series Detectors
BNC Female Output (Photodetector)
PDA10A2, PDF10A, PDA015A, PDA100A2, PDA36A2: 0 - 10 V Output
Male (Power Cables)
Female Power IN (Photodetector)
FPD Series Detectors
Signal Out- SMA Female (Photodetector)
For connection to a suitable monitoring device, e.g. oscilloscope or RF-spectrum-analyzer, with 50 Ω impedance.
Female (Power Cables)
Male Power IN (Photodetector)
Theory of Operation
A junction photodiode is an intrinsic device that behaves similarly to an ordinary signal diode, but it generates a photocurrent when light is absorbed in the depleted region of the junction semiconductor. A photodiode is a fast, highly linear device that exhibits high quantum efficiency based upon the application and may be used in a variety of different applications.
It is necessary to be able to correctly determine the level of the output current to expect and the responsivity based upon the incident light. Depicted in Figure 1 is a junction photodiode model with basic discrete components to help visualize the main characteristics and gain a better understanding of the operation of Thorlabs' photodiodes.
Modes of Operation (Photoconductive vs. Photovoltaic)
The dark current present is also affected by the photodiode material and the size of the active area. Silicon devices generally produce low dark current compared to germanium devices which have high dark currents. The table below lists several photodiode materials and their relative dark currents, speeds, sensitivity, and costs.
Bandwidth and Response
Noise Equivalent Power
Here, S/N is the Signal to Noise Ratio, Δf is the Noise Bandwidth, and Incident Energy has units of W/cm2. For more information on NEP, please see Thorlabs' Noise Equivalent Power White Paper.
Depending on the type of the photodiode, load resistance can affect the response speed. For maximum bandwidth, we recommend using a 50 Ω coaxial cable with a 50 Ω terminating resistor at the opposite end of the cable. This will minimize ringing by matching the cable with its characteristic impedance. If bandwidth is not important, you may increase the amount of voltage for a given light level by increasing RLOAD. In an unmatched termination, the length of the coaxial cable can have a profound impact on the response, so it is recommended to keep the cable as short as possible.
Common Operating Circuits
The DET series detectors are modeled with the circuit depicted above. The detector is reverse biased to produce a linear response to the applied input light. The amount of photocurrent generated is based upon the incident light and wavelength and can be viewed on an oscilloscope by attaching a load resistance on the output. The function of the RC filter is to filter any high-frequency noise from the input supply that may contribute to a noisy output.
One can also use a photodetector with an amplifier for the purpose of achieving high gain. The user can choose whether to operate in Photovoltaic of Photoconductive modes. There are a few benefits of choosing this active circuit:
where GBP is the amplifier gain bandwidth product and CD is the sum of the junction capacitance and amplifier capacitance.
Effects of Chopping Frequency
The photoconductor signal will remain constant up to the time constant response limit. Many detectors, including PbS, PbSe, HgCdTe (MCT), and InAsSb, have a typical 1/f noise spectrum (i.e., the noise decreases as chopping frequency increases), which has a profound impact on the time constant at lower frequencies.
The detector will exhibit lower responsivity at lower chopping frequencies. Frequency response and detectivity are maximized for
The following table lists Thorlabs' selection of photodiodes and photoconductive detectors. Item numbers in the same row contain the same detector element.
The PDA-C-72 power cord is offered for the PDA line of amplified photodetectors when using with a power supply other than the one included with the detector. The cord has tinned leads on one end and a PDA-compatible 3-pin connector on the other end. It can be used to power the PDA series of amplified photodetectors with any power supply that provides a DC voltage. The pin descriptions are shown to the right.
The LDS12B ±12 VDC Regulated Linear Power Supply is intended as a replacement for the supply that comes with our PDA and PDF line of amplified photodetectors sold on this page. The cord has three pins: one for ground, one for +12 V, and one for -12 V (see diagram above). A region-specific power cord is shipped with the LDS12B power supply based on your location. This power supply can also be used with the PDB series of balanced photodetectors, PMM series of photomultiplier modules,APD series of avalanche photodetectors, and the FSAC autocorrelator for femtosecond lasers.
These internally SM1-threaded (1.035"-40) adapters mate connectorized fiber to any of our externally SM1-threaded components, including our photodiode power sensors, our thermal power sensors, and our photodetectors. These adapters are compatible with the housing of the photodetectors on this page.
Each disk has four dimples, two in the front surface and two in the back surface, that allow it to be tightened from either side with the SPW909 or SPW801 spanner wrench. The dimples do not go all the way through the disk so that the adapters can be used in light-tight applications when paired with SM1 lens tubes. Once the adapter is at the desired position, use an SM1RR retaining ring to secure it in place.