composition of IR filters

I know this is a dumb questions, but what are IR filters made of?

I know that some companies (like Optotronics and NOVAlasers) sell IR filters that users can add to their lasers. However, IR filters often come in one large piece.

Are they generally made of glass or plastic? Glass optics are more resilient to scratches and other wear, but they also shatter to stress more easily. In that case, are there any safe methods for cutting an IR filter into smaller pieces?

Good IR filters are made of glass. The best for blue/green lasers are Schott BG38 filters. Here's a datasheet for them:http://www.optical-filters.com/bg38.html

You can see from the graph in the datasheet that they pass >90% of blue/green and block >95% of IR. To my knowledge, only BG38s will allow for these low losses while blocking such a substantial amount of IR. Novalasers and Snoctony both sell filters that come somewhat close to these numbers. The filters from optotronics, while cheap, are highly ineffective..

Personally I buy mine from here: http://search.stores.ebay.com/Omega...yer2QQfsooZ1QQfsopZ1QQsaselZ164036161QQsofpZ0

Also, I occasionally sell them on this forum in the buy/sell/trade section whenever I have any extras that I won't be using..

About cutting: You can cut glass filters with a glass cutter if you are very careful, but your best bet is to order one that is already the right size (or close enough)..

There are several options to block IR but let visible light get through. Glass filters have the clear advantage of better thermal conduction and are less sensitive to temperature in the first place, so can handle absorbing a lot more ir than plastics can... compare this to plastic vs glass color filters.

Another possibility is a filter with a (dielectric) coating instead of a dye. This is very commonly used 'in reverse' for deeper IR in, for example, halogen lightbulb reflectors (so as to focus the light but not the heat). If used with a laser, such filters should be inserted at an angle to prevent reflecting the IR straight back into the laser.

Benm said:

There are several options to block IR but let visible light get through. Glass filters have the clear advantage of better thermal conduction and are less sensitive to temperature in the first place, so can handle absorbing a lot more ir than plastics can... compare this to plastic vs glass color filters.

Another possibility is a filter with a (dielectric) coating instead of a dye. This is very commonly used 'in reverse' for deeper IR in, for example, halogen lightbulb reflectors (so as to focus the light but not the heat). [highlight]If used with a laser, such filters should be inserted at an angle to prevent reflecting the IR straight back into the laser.[/highlight]

Click to expand...

VERY important! I'm glad you said that, Benm. Doing this will also help keep the beam clean and free of noise and reflections. This should really be done with any filter that is not AR coated (and even with AR coatings if you ask me).