# Low-cost low threshold optical beam limiter?

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1. Sep 16, 2015

Do you guys know a low-cost low-threshold optical beam limiter, with cost somewhere ~$100. Or if you know certain method to fabricate such. I would be greatful if you could include links and/or references. I am still noob in photonics so I am only familiar with a beam limiter that blocks the entire incoming lase beam when its intensity is at a certain threshold of the beam limiter. In other case the beam limiter will always permit laser beam that has less than the threshold intensity. 2. Sep 18, 2015 ### berkeman ### Staff: Mentor What wavelength is your laser? Perhaps you could use a configuration with a Photchromic Lens: https://en.wikipedia.org/wiki/Photochromic_lens For higher beam intensities, the lens will darken more, letting less of the beam through... 3. Sep 18, 2015 ### Andy Resnick It's not clear what you are looking for- first, what is/are the wavelengths? What are the ranges of input power and output power? What timescale does the intensity adjustment require- seconds, nanoseconds...? What is the cross-section of the optical beam? Etc. etc. etc. 4. Sep 21, 2015 ### flux! I will certainly look into photochromatic lenses :) By the way, we got this laser: Wavelength: Red, 620–750 nm Power: 1 mW Cross-section: 1 mm Diameter Timescale intensity adjustment: No idea, newbie photonics researcher here. Optical Beam Limiter I am looking: Price: Low cost (I got$2000 research grant, that is already everything)
Activation time: 1 ns or faster (I mean, instant activation when the threshold is reached)

5. Sep 21, 2015

### Staff: Mentor

You could also do a manual rotary optical attenuator disc if that met your experimental requirements...

6. Sep 22, 2015

### Andy Resnick

If I understand you correctly, you are working with a Class II CW laser (ANSI Z-136.1 standard), which doesn't require anything fancy, a simple mechanical shutter or beam blocker will suffice- your 'blink response' provides sufficient protection to accidental exposure. The laser output power is constant, yes?

Or am I misunderstanding the problem you are trying to solve?

7. Sep 23, 2015

### flux!

Yes, the power is constant, as much as possible I would like to avoid mechanical parts, right now I am looking into photochromatic lenses, but would welcome other types of lenses/material, could you suggest a link to simple blocker?

8. Sep 23, 2015

### Andy Resnick

I get that you are itching to buy something, I'm trying to slow you down to first figure out exactly what you need. I guess I still don't understand what problem you are trying to solve (and I don't mean 'the problem is that I need to buy an optical limiter'). For example:

1) Is this 'limiter' device intended to make the laser eye-safe? Class II devices are best made eye-safe manually- turn the laser off or shutter the beam when needed, use goggles when the laser is on, things like that. Class III and Class IV lasers require automatic shut-offs- door interlocks, for example- in addition to other controls.

2) Is this device intended for some other purpose, for example, learning about laser safety and designing the appropriate controls?

3) How is the laser being used? For example, will this be a laser taken into a large lecture hall that makes use of goggles impractical? Is the laser in a laboratory setting with a few people near the beam? Is the laser fixed in position, or will it be moved from place to place?

4) Where is the beam going? Is it going into a free-space optical system where the possibility of accidental scattering/errant beam is moderate, or is the beam going into an enclosed device (spectrometer, etc)?

If you just want to buy a photochromic lens and move on, by all means go ahead- but realize that you may not have solved your problem.

9. Sep 23, 2015

### Staff: Mentor

If you want nanosecond activation time, I don't think photochromic lenses will work for you.

10. Sep 24, 2015

### flux!

Yhea, thanks for pointing that out, I guess photochromic lenses will be listed out.

Its more like number 4, the beam will go into an enclosed device, no other peoples eyes will get hurt. I am planning to supper impose monochromatic red beams and the limiter will act like a fast switch when a threshold is reached.