# What is Photodetector: Definition and 18 Discussions

Photodetectors, also called photosensors, are sensors of light or other electromagnetic radiation. There is a wide variety of photodetectors which may be classified by mechanism of detection, such as photoelectric or photochemical effects, or by various performance metrics, such as spectral response. Semiconductor-based photodetectors typically have a p–n junction that converts light photons into current. The absorbed photons make electron–hole pairs in the depletion region. Photodiodes and phototransistors are a few examples of photodetectors. Solar cells convert some of the light energy absorbed into electrical energy.

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1. ### Procedure to express radiation intensity of an LED in watts/cm^2

I am calculating Responsivity of a pn junction photodiode (a.k.a the target) by irradiating radiation from LED sources. For this purpose, i have two LEDs, one UV and another green LED. Note that LEDs are placed close to the target.UV LED : Manufacturer has given total radiant power to be 20mW...
2. ### How to measure the bandwidth of a photodetector?

I am new to photodetectors. I know there are usually two concepts of bandwidths of photodetectors, i.e the spectral and electrical. What I do not understand is the electrical bandwidth. The electrical bandwidth is used to calculate the shot noise of a photodetector. However, the papers usually...
3. ### I Photodiode bandwidth: why does power decrease with frequency

Hi, I'm studying p-i-n photodiode (PD) at the moment and understand that the photodiode's response will depend on the frequency of the light signal going into it. I am struggling however to understand the concept of bandwidth, and why is it that the photocurrent at the PD decreases with higher...
4. ### I Minimizing diffraction in images using a photodetector

If I understand the phenomenon correctly; whenever we capture an image using a telescope, because the light that's emitted from a distance object acts like a wave, we notice a diffraction pattern in our image. Now, in the double slit experiment (I didn't create the image, excuse the "slot"...
5. ### Fundamental noise limit for an ideal photodetector

Homework Statement As the title says, I'm trying to calculate the fundamental noise limit for an ideal photodetector, by specifically looking at the rate of incidence of annihilation of photons (and subsequent excitation of conducting electrons) on the detection surface. Since I'm looking for...
6. ### B Interferometry on photodetector

Hello! I am trying an interferometry experiment using the Michelson Morley experiment. I managed to obtain the interference pattern on a screen, but I want to use an photodetector and I am not sure what should I obtain. As I know, the oscilloscope shows the intensity of the light, so if I modify...
7. ### Complete Noise Analysis: to find the minimum detectable signal

Problem Statement: my aim is to digitalize a 10ns narrow pulse coming from a photo diode with current ranging from 10nA-70mA, as its impossible to cover this dynamic range of >60dB using a single TIA i have an option of separating it to two channels as below using two diodes ofcourse Lowest...
8. ### Photodetector Bonanza: Buy & Learn for 4-Week EE Project

Here's the thing: I'm a god-fearing humble man like yourselves, but I know jack about electrical engineering, yet I've found myself in a rather peculiar situation. In particular, I'm supposed to perform electrical engineering. So, we're supposed to design a model of a theoretical city, using...
9. ### Optical Adder Using 2 Lasers & Selectable Intensities

If we use 2 lasers with selectable light intensities as input, with each level of intensity corresponding to decimal number. Like level 0 intensity - decimal 0 (MIN) level 1 intensity - decimal 1 level 2 intensity - decimal 2 ... level 9 intensity - decimal 9 (MAX) and directly shine both of...
10. ### Why is Biasing Important for Photodetectors?

Hello I just want to ask why do we bias the photodetector before starting any setup? Thank you
11. ### What is photodetector bandwidth?

Hi, I would like to know how a detectors bandwidth can be measured? for example, if there is any relation with the produced current or what? I can't understand bandwidth concept. Thank you.
12. ### Is possible to use interband transition to design mid-infrared photodetector?

Is it possible to use interband transition to design mid-infrared photodetector? I want to design mid-infrared photodetector based on interband transition. I could not find any article that use interband transition for mid-infrared photodetector.
13. ### Understanding PIN Photodetector Bandwidth for Vibration Sensing

I'm trying to design a fiber optic sensor to sense vibration via intensity modulation. I'm new in this field and i don't know whether I can use a PIN photodetector for low frequency or not... what's the bandwidth of a PIN Photodetector? Does it mean its responsivity is limited in low frequency...
14. ### LED photodetector IV curves

I was wondering if anybody could help me understand my measurements. I was interested in measuring the photo current and voltage of a red LED placed in room light and sun light. I measured the voltage across the LED and the current through in both conditions. In the room measurement, I am...
15. ### Need help with a sensor circuit using a photodetector

hello, I am currently working on a simple school project to make a sensor circuit. i need the circuit to include a photodetector (either photodiode, phototransistor or LDR) to sense and measure the intensity of a typical laser beam (from a cheap laser pointer), the main aim is to get a different...
16. ### Photodetector in single-slit experiment

I have a lay question that needs answering please. If a photodetector can display a single 'white dot blip' where a single photon has struck it, how can this be explained without requiring a physical size of the incident photon? Side Questions 1) Does a photon of higher energy leave a...
17. ### Creating a Light-Activated Switch with a Photodetector Circuit

How would one set up a circuit where a photodetector closes a switch in a circuit once it detects light?
18. ### Photodetector vs. Photosensor: Infrared Light & Point Source

Help! is a photo detector the same as photosensor? can they be specifically for infrared light? and what does point source mean?