How to build a DIY laser power meter

In summary: So you need a DVM, some LEDs, and a resistor.You can connect the DVM across the photodiode and shine some light on the LED -- you get a voltage from the photocurrent flowing through the DVM's measurement resistance.Then better is to learn how to make a current-to-voltage converter circuit with an opamp and a reverse-biased photodiode.
  • #1
David lopez
257
3
How do I build diy laser power meter. I tried shining 5 milliwatt laser on photodiode. Photodiode is connected to led. Led never turned on.
 
Physics news on Phys.org
  • #2
David lopez said:
How do I build diy laser power meter. I tried shining 5 milliwatt laser on photodiode. Photodiode is connected to led. Led never turned on.
Do you have a DVM? Connect the DVM across the photodiode and see what you get for an output voltage (it will max out at a couple of volts).

Then better is to learn how to make a current-to-voltage converter circuit with an opamp and a reverse-biased photodiode. Have you worked with opamps or other circuits yet?
 
  • #3
berkeman said:
Do you have a DVM? Connect the DVM across the photodiode and see what you get for an output voltage (it will max out at a couple of volts).
See this reply from a different thread, for example:
berkeman said:
Not true. Hook an LED to a DVM and shine some light on the LED -- you get a voltage from the photocurrent flowing through the DVM's measurement resistance. :smile:

There's an important reason to use at least a few volts of reverse bias across the photodiode -- it has to do with bandwidth. Do a little Google searching to see if you can find a good explanation of that, and post it here. :smile:

LED under a lamp with DVM measuring the voltage (Red positive lead on the LED anode):

View attachment 240669
 
  • #4
Actually I tried connecting the photodiode to a digital multimeter and shining a 5 milliwatts laser pointer onto the photodiode. The measured resistance Didn't change.
 
  • #5
I have worked with operational amplifiers before.
 
  • #6
David lopez said:
The measured resistance Didn't change.
Measure junction voltage with the DVM, not resistance.
 
  • #7
David lopez said:
I have worked with operational amplifiers before.
This is the classic reverse-biased current-to-voltage converter circuit that is used with photodiodes to measure the photocurrent:

https://www.electronics-tutorial.net/wp-content/uploads/2015/09/I_to_V3.png
244272


The reverse bias on the photodiode makes it more linear, and improves the bandwidth of the detection (like if you were using it in a communication link as a receiver).
 
  • Like
Likes dlgoff
  • #8
The usual light meter / Laser power meter, is a photovoltaic cell, such a Selenium photo cell or a Silicon photo cell, connected to a load resistor and a moving-coil meter.

Since the photovoltaic cell current output is proportional to received power, the load resistor is connected across the cell and the meter reads the voltage.

Here is an old photographic exposure meter based on that principle.
ExposureMeter.png
ExposureMeter.png
Some (all?) of the exposure meters just use the resistance of the meter as the load, avoiding the additional load resistor.

On simple Laser power meters you change ranges by switching in different load resistors.

The main advantages of this approach are no battery or electronics are needed, very low cost, and the cells have enough active area that you don't need any optics to focus the Laser beam to a tiny photo diode.

A DIY meter will of course require calibration, that's why most folks buy a digital power meter. Google showed one for US$35 when I searched for 'camera exposure meter.'

Cheers,
Tom

Edit: added photo, reference to Silicon cell

p.s. the circular dial on the exposeure meter is just a circular slide rule to compute camera aperture and shutter speed, based on light level and film speed. It has no electrical connection to the metering function.
 
Last edited:
  • Like
Likes dlgoff and berkeman
  • #9
berkeman said:
Measure junction voltage with the DVM, not resistance
Voltage is not linear with incident intensity. It is much better to measure the photocurrent.
You can add reverse bias with a single battery.
 
  • Like
Likes berkeman

1. How does a DIY laser power meter work?

A DIY laser power meter works by measuring the amount of light energy produced by a laser. This is done by using a photodiode, which converts light into an electrical current. The current is then measured and converted into a power reading using a circuit or software.

2. What materials are needed to build a DIY laser power meter?

The materials needed to build a DIY laser power meter include a photodiode, a voltmeter, a resistor, a power source, and a housing or enclosure. Optional materials include a microcontroller or software for data analysis.

3. Is it safe to build and use a DIY laser power meter?

As long as proper safety precautions are taken, building and using a DIY laser power meter can be safe. It is important to wear appropriate eye protection and handle the laser with care to avoid any accidents.

4. Can a DIY laser power meter be used for all types of lasers?

Yes, a DIY laser power meter can be used for most types of lasers as long as the power output is within the range that the meter is designed for. It is important to check the specifications of the meter and make sure it is compatible with the laser being measured.

5. Are there any resources or tutorials available for building a DIY laser power meter?

Yes, there are many online resources and tutorials available for building a DIY laser power meter. These can be found on websites, forums, and video platforms such as YouTube. It is important to follow a reliable and detailed tutorial to ensure the accuracy and safety of the meter.

Similar threads

Replies
4
Views
2K
  • General Engineering
Replies
1
Views
1K
  • DIY Projects
Replies
4
Views
2K
  • DIY Projects
Replies
2
Views
1K
  • DIY Projects
Replies
5
Views
2K
  • Electrical Engineering
Replies
12
Views
1K
  • Electrical Engineering
Replies
5
Views
846
Replies
31
Views
2K
  • DIY Projects
Replies
7
Views
2K
  • DIY Projects
Replies
2
Views
1K
Back
Top