# Diffusion of laser light for measuring laser power

• jodyflorian
In summary, the author is trying to build a meter to measure laser power accurately to around 10% accuracy. One building block he is using is a phototransistor, which has a good linear response when measuring mW/m^2. However, the main hurdle he is having trouble over is finding a diffuser with known properties for light scattering.
jodyflorian
Hi,

I've decided to make my own meter for measuring laser power to around 10% accuracy if possible. Optical power meters are way too expensive for me though.

One building block I've decided to use is a phototransistor, because I've found one which has very good linear response - when measuring mW/m^2. (Its datasheet has a graph showing collector current for the said power per area). The data sheet also has a response graph for various light frequencies which will be easy to use since lasers have a very specific color e.g. 532nm for green).

However, the hurdle I'm having trouble getting over is the diffuser. In principle, (please correct me if I'm wrong), if I know the following properties for a diffuser, it should be easy to calculate the laser power, given:

1) Distance of phototransistor from the diffuser
2) Placement position of phototransistor with respect to the diffuser
3) Light scattering pattern of the diffuser for various angles (inc. reflection)
4) Absorbtion factor of the diffuser.
5) (values of 3 and 4 for the given laser frequency)

However, I'm having trouble finding anything I can use as a diffuser where 3, 4 and 5 are known. I don't have many, if any, tools to do this myself...
a) Multimeter
b) Oscilloscope
c) Lux meter
c) Three lasers of unknown power (in the 1 to 20 milliwatt range, I expect)

i) Buying cheap LEDs of known frequency and output power for calibrating
ii) Buying a diffuser with the above known properties (3, 4, 5)

Thanks :)

I'm confused- why do you want to use a diffuser? There are good reasons (polarization, stability, etc), but when measuring optical power, the diffuser is something called an 'integrating sphere'. Perhaps you could construct an inexpensive one that meets your needs- I bet spraying the inside of a ball with that popcorn paint stuff (seen on 1970's era ceilings) would work fine.

Lol @ popcorn paint. Brilliant - now I know the term! "Integrating Sphere".

I'm just trying to find the cheapest way of measuring laser output so I can judge lasers that I buy off ebay, and optical power meters seem to go for no less than £150 so about \$250.

The main hurdle I'm coming up against is that anything I build myself seems to need calibration with lasers of known power output - which I dont' have!

I was thinking that if I bought a diffuser with known properties, and use a phototransistor with known properties, I wouldn't need to calibrate it.

The only alternative apparently involves measuring the cross sectional area of the beam, which my gut feel says would be really quite inaccurate and a fair amount of work for each laser that I test... (This would use the Lux meter and I'm not comfortable with the calculations involved!)

I really like the idea of using an Integrating Sphere, but I assume if I build my own it would still need calibration! I've just done a search on google and found a few suppliers but no prices and no specs... should I just look harder, or am I facing a brick wall here? I'd need to know the proportion of light falling on the sphere's surface vs the amount being absorbed, for given frequencies, I assume? Is this a typical value that should really be readily available from the manufacturers or am I missing the point? Just a thought as well... I have a horrible feeling that a ready made integrating sphere could cost more than £150!? DOH!

Thanks!

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## What is diffusion of laser light?

Diffusion of laser light is the process by which a laser beam spreads out as it travels through a medium. This happens due to interactions between the laser light and the molecules in the medium, causing the laser beam to scatter.

## How is diffusion of laser light measured?

Diffusion of laser light can be measured using a technique called laser power measurement. This involves directing the laser beam onto a target and measuring the amount of light that is scattered or absorbed by the target. The amount of diffusion can then be calculated based on this measurement.

## What is the importance of measuring laser power?

Measuring laser power is important for a variety of reasons. It allows scientists to understand the properties of a laser beam, such as its intensity and energy output. This information is crucial for many applications, including medical treatments, industrial processes, and scientific research.

## How does diffusion of laser light affect laser power?

Diffusion of laser light can decrease the power of a laser beam as it spreads out. This decrease in power is due to the energy being distributed over a larger area as the beam diffuses. However, this diffusion can also be controlled and utilized in certain applications, such as in laser cutting and welding.

## What factors can affect the diffusion of laser light?

The diffusion of laser light can be affected by several factors, including the type of medium the laser beam is traveling through, the wavelength of the laser, and the power of the laser. Additionally, the angle and distance of the laser beam from the target can also impact the amount of diffusion.

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