# How to get a 30um (micrometer) laser diameter?

• FourierTransform
In summary: The lens equation won't help because it's dealing with an entire lens system and you're just looking at a point.There are many affordable microscopes that can do this- I'm not sure what the cost is, but you could check out ebay or google.If this laser blows and won't work for my purposes. Can anyone point me in the right direction for a set up that would cost under $300?There are many affordable microscopes that can do this- I'm not sure what the cost is, but you could check out ebay or google. FourierTransform Greetings everyone. I am a mechanical engineering student whose professor challenged him to a project that requires some optics knowledge. After years of quietly reading the physics forums I am finally making my first post. If this question ends up in the wrong forum, feel free to move it to the correct one. So I am building an Atomic Force Microscope (at least trying to), if anyone has any knowledge of them. Basically I need to reflect a laser off a cantilever of diameter 30um (positioned at an 11 degree angle), and into a photo-detector. My lab has this laser: https://www.thorlabs.com/thorproduct.cfm?partnumber=CPS635F which claims to have a 30um diameter when focused. Well, when I test the laser on surfaces such as walls, tables, etc, the diameter surely does not look 30um. However I am not sure if this is because the rating is off, or the surfaces are just reflecting the laser in many directions and making it appear wider. My first question: I have a suspicion that if the laser diameter is larger than the cantilever, that there will still be light reflected off of it, and therefore having the laser focused to under 30um is not necessary. Is this correct? Or would it greatly benefit me to reduce the laser diameter? My second question: Is the laser we have capable of being focused to 30um if that is a necessary or desirable goal? Thirdly: If this laser blows and won't work for my purposes. Can anyone point me in the right direction for a set up that would cost under$300?
I tried doing some physics last week using some lens equations but wasn't having much luck. If anyone has any suggestions, I would really appreciate it.

FourierTransform said:
If anyone has any suggestions, I would really appreciate it.

Not exactly sure what your setup is like, but it's easy to focus a laser down to 30um- expand it so it fills the back aperture of a microscope objective, and presto- at the focus the beam waist can be made as small as the diffraction limit. Put the cantilever at the beam waist, the reflected beam will go back through the objective and emerge at an angle relative to the incident beam- that's the principle of an optical cantilever.

FourierTransform said:
the diameter surely does not look 30um
You can never see the actual size of that spot: 30 ##\mu ##m is less than a hair. All your eyes can make of it is a bright dot. You'll need to scan across with a ##< 10 \mu##m slit to measure the spatial intensity distribution.

BvU said:
You can never see the actual size of that spot: 30 ##\mu ##m is less than a hair. All your eyes can make of it is a bright dot. You'll need to scan across with a ##< 10 \mu##m slit to measure the spatial intensity distribution.

Or just wear appropriate goggles

## 1. How is the laser diameter measured?

The laser diameter can be measured using a micrometer or a laser beam profiler. A micrometer is a tool used to precisely measure small distances, while a laser beam profiler is a device that captures the intensity profile of a laser beam.

## 2. What factors affect the laser diameter?

The laser diameter can be affected by several factors, such as the type of laser used, the quality of the optics, the alignment of the laser, and the stability of the power source. Environmental factors, such as temperature and humidity, can also have an impact on the laser diameter.

## 3. How can I achieve a 30um laser diameter?

To achieve a 30um laser diameter, you will need to use a high-quality laser with precise optics and proper alignment. Additionally, controlling environmental factors and using a stable power source can help to achieve a consistent laser diameter.

## 4. Can the laser diameter be adjusted?

Yes, the laser diameter can be adjusted by changing the focal length of the lens or by using different optics. Some lasers also have adjustable output settings that can affect the diameter of the beam.

## 5. Are there any safety precautions to consider when working with a 30um laser?

Yes, it is important to wear appropriate safety gear, such as laser safety glasses, when working with any laser. It is also crucial to follow proper handling and operation procedures to prevent accidents or injuries. Additionally, ensure that the laser is properly shielded to prevent accidental exposure to the beam.

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