# Laser Beam Travel **URL:** \ **Category:** Factual Questions\ **Created:** [February 22, 2013, 10:39am UTC](https://boards.straightdope.com/t/laser-beam-travel/651082 "2013-02-22T10:39:51Z")\ **Posts on this page:** 7\ **Page:** 1
**Author:** ![wajahat\_ali](https://avatars.discourse-cdn.com/v4/letter/w/977dab/32.png) [@wajahat\_ali](https://boards.straightdope.com/u/wajahat_ali)\ **Post date:** [February 22, 2013, 10:39am UTC](https://boards.straightdope.com/t/laser-beam-travel/651082/1 "2013-02-22T10:39:51Z")
i m working on a project where i m using laser as transmitter and IR as receiver. when laser beam falls on IR receiver it gives output which goes to controller and performs others tasks. i m using many IR receiver in matrix form and all are closed to each other. laser beam pulses/bursts will fall any of the IR receiver that only one should operate. now, the problem is that when sudden pulse falls on any of IR receiver, some other IR receivers near to it also operated. i dont understand what is the Problem. anyone can help me on this Problem? i will be thankful to all helping me in this regard thanx wajahat ali ---
**Author:** ![Mangetout](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/mangetout/32/19_2.png) [@Mangetout](https://boards.straightdope.com/u/Mangetout)\ **Post date:** [February 22, 2013, 10:50am UTC](https://boards.straightdope.com/t/laser-beam-travel/651082/2 "2013-02-22T10:50:25Z")
> [@wajahat\_ali](#): > > i m working on a project where i m using laser as transmitter and IR as receiver. when laser beam falls on IR receiver it gives output which goes to controller and performs others tasks. i m using many IR receiver in matrix form and all are closed to each other. laser beam pulses/bursts will fall any of the IR receiver that only one should operate. > now, the problem is that when sudden pulse falls on any of IR receiver, some other IR receivers near to it also operated. i dont understand what is the Problem. > anyone can help me on this Problem? > i will be thankful to all helping me in this regard > thanx > wajahat ali It probably would have been better to ask this question in a new thread - I’ve reported this and a moderator will hopefully be able to break it off as a new OP. It sounds to me like your problem is halation - that is, the incident light is hitting the sensor, then being scattered sideways to trigger adjacent sensors. If so, it may be possible to overcome the problem by fitting a hood around each sensor - just a little piece of opaque plastic tube so the sensor can only ‘see’ in a forward direction. Edited to add: if that doesn’t fix it, then your problem might be beam spread. ---
**Author:** ![AaronX](https://avatars.discourse-cdn.com/v4/letter/a/7bcc69/32.png) [@AaronX](https://boards.straightdope.com/u/AaronX)\ **Post date:** [February 22, 2013, 11:04am UTC](https://boards.straightdope.com/t/laser-beam-travel/651082/3 "2013-02-22T11:04:52Z")
How big are the receivers? Can you use one of those privacy screen protectors? Yesterday I was thinking of making a self-read height gauge with them. ---
**Author:** ![Mangetout](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/mangetout/32/19_2.png) [@Mangetout](https://boards.straightdope.com/u/Mangetout)\ **Post date:** [February 22, 2013, 12:56pm UTC](https://boards.straightdope.com/t/laser-beam-travel/651082/4 "2013-02-22T12:56:30Z")
> [@AaronX](#): > > How big are the receivers? Can you use one of those privacy screen protectors? Yesterday I was thinking of making a self-read height gauge with them. That’s a good idea, but is the distance between eye level and crown the same for everyone? ---
**Author:** ![Gary\_Robson](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/gary_robson/32/3448_2.png) [@Gary\_Robson](https://boards.straightdope.com/u/Gary_Robson)\ **Post date:** [February 22, 2013, 3:15pm UTC](https://boards.straightdope.com/t/laser-beam-travel/651082/5 "2013-02-22T15:15:47Z")
> [@Mangetout](#): > > It probably would have been better to ask this question in a new thread - I’ve reported this and a moderator will hopefully be able to break it off as a new OP. [moderating] Yes, indeed. A moderator is able to do exactly that. 😃 [/moderating] ---
**Author:** ![scr4](https://avatars.discourse-cdn.com/v4/letter/s/59ef9b/32.png) [@scr4](https://boards.straightdope.com/u/scr4)\ **Post date:** [February 22, 2013, 3:27pm UTC](https://boards.straightdope.com/t/laser-beam-travel/651082/6 "2013-02-22T15:27:18Z")
> [@wajahat\_ali](#): > > i m working on a project where i m using laser as transmitter and **IR as receiver**. I’m not sure what that means (the part I bolded) - IR as in infrared? Did you mean to say IR photodiode? How far apart are the detectors, and how large is the laser beam at the detector? My WAG is that diffraction and/or scattering is creating a halo around the laser spot which is bright enough to activate the sensor. You need to reduce the intensity of the laser and/or decrease the sensitivity of the detectors to make sure that the detectors only respond to the central core of the laser beam. ---
**Author:** ![AaronX](https://avatars.discourse-cdn.com/v4/letter/a/7bcc69/32.png) [@AaronX](https://boards.straightdope.com/u/AaronX)\ **Post date:** [February 22, 2013, 3:37pm UTC](https://boards.straightdope.com/t/laser-beam-travel/651082/7 "2013-02-22T15:37:33Z")
> [@Mangetout](#): > > That’s a good idea, but is the distance between eye level and crown the same for everyone? Oh, so here’s where this post went. No, it’d be like using stride length to guess your height. Or shoe size to guess.. nevermind