# Laser connected to photodiode to measure potential?

• Levi Tate
In summary, this lab was simply to measure a potential difference with a laser. The photodiode created the potential difference and the voltmeter measured it.
Levi Tate

## Homework Statement

I am doing a lab and need to understand how laser light from a HeNe laser goes into a Si photodiode connected to a lock in amplifier, which I believe is simply a device for measuring potential, works.

## The Attempt at a Solution

This lab was extremely simple, we shot a laser through a beaker of water with food die in it, the laser went through the beaker into an Si photodiode, which was connected to an instrument to measure voltage. What I do not understand is how the light produces a potential difference in the Si photodiode.

If anybody can provide an explanation or refer me to relevant literature, it would be of great help to me.

Thanks

You don't know how a photodiode works?
Crudely - it converts electrical energy in the light to electrical energy in the circuit.

What I am asking is, how does the photodiode take the incident light, which is connected to a voltmeter, and measure the potential difference of the light.

I don't understand how the light creates a potential difference and how the photodiode, which is connected to the voltmeter, (we're using a lock in amplifier), measures it.

The voltmeter does not measure the potential difference of the light - have a look at the photodiode circuits in the link I gave you.

The voltage is across part of the ciruit that includes a photodiode - what it is measureing exactly depends on circuit. The designer of the circuit arranged so that the voltage on the voltmeter was proportional to the intensity of light that hits the photodiode.

The diode itself works using a form of the photoelectric effect. Incoming photons knock electrons off the material of the diode, the freed electrons travel to one end creating a potential difference. The more photons that hit the bigger the difference.

It's kinda the opposite of how an LED works.

Alright yeah, thanks mate, the part about the diode being like a photoelectric effect kind of makes sense to me.

No worries - it is difficult to know where to pitch the answers.
Wikipedia has links to more detailed descriptions of how it works if you need it.

## 1. What is the purpose of connecting a laser to a photodiode in order to measure potential?

The laser and photodiode combination is used to measure the potential difference between two points by converting the light intensity from the laser into an electrical signal through the photodiode. This allows for precise and non-invasive measurements of potential in various scientific experiments and applications.

## 2. How does the laser and photodiode setup work to measure potential?

The laser emits a beam of light, which is directed onto the photodiode. The photodiode is made of a semiconductor material that converts light into an electrical current. The amount of current produced is proportional to the intensity of the laser light, which is affected by the potential difference between the two points being measured. This current is then amplified and measured to determine the potential difference.

## 3. What are the advantages of using a laser and photodiode to measure potential?

The laser and photodiode setup offers several advantages over traditional methods of measuring potential. It is non-invasive, meaning it does not physically touch the object being measured, making it useful for delicate or sensitive materials. It also has a high accuracy and precision, allowing for precise measurements in a variety of conditions. Additionally, the setup is compact and can be easily integrated into other equipment or setups.

## 4. Are there any limitations to using a laser and photodiode to measure potential?

While the laser and photodiode setup has many benefits, there are also some limitations to consider. The accuracy and precision of the measurements may be affected by environmental factors such as temperature, humidity, and ambient light. Additionally, the setup may not be suitable for measuring potentials that change rapidly, as the photodiode may not be able to keep up with the changes in light intensity.

## 5. What are some common applications of using a laser and photodiode to measure potential?

The laser and photodiode setup is commonly used in various scientific and industrial applications. It is often used in electrochemistry to measure the potential difference between electrodes, in materials science to study the properties of materials, and in biomedical research for non-invasive measurements of biological potentials. It is also used in quality control and testing of electronic components, as well as in environmental monitoring and energy production processes.

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