Invisible"ink" on white paper with 1W 405nm

[Jirkas99]

While I played with my BDR-209 build I noticed something interesting.
When you try to burn a paper with a bit unfocused dot and stop before it turns black it creates burn mark that can't be seen in normal light but can be seen in uv light so you can use it to write like with invisible ink pen

Paper under normal light:


When illuminated with 365nm flashlight:

Edit: I didn't tried other colored papers.I will try it soon and post results here.
Edit 2: It works with light yellow and other colors(but color has to be fluorescent enough)but best is white, I can't look at yellow paper even thru safety glasses because of fluorescence

 

[CurtisOliver]

You've burnt away the fluorescent compounds that were added to the paper to make them appear whiter. It probably won't work in the same way with other coloured paper. But it's worth a try. Nice little find.

 

[steve001]

While I played with my BDR-209 build I noticed something interesting.
When you try to burn a paper with a bit unfocused dot and stop before it turns black it creates burn mark that can't be seen in normal light but can be seen in uv light so you can use it to write like with invisible ink pen

Paper under normal light:
View attachment 64760

When illuminated with 365nm flashlight:
View attachment 64761
Edit: I didn't tried other colored papers.I will try it soon and post results here.
Edit 2: It works with light yellow and other colors(but color has to be fluorescent enough)but best is white, I can't look at yellow paper even thru safety glasses because of fluorescence

You'll discover many things will fluoresce and some materials are phosphorescent.

 

[Jirkas99]

You'll discover many things will fluoresce and some materials are phosphorescent.

Yeah, thats why near UV and UV wavelengths are my favorites.

 

[steve001]

Yeah, thats why near UV and UV wavelengths are my favorites.

See if there are rocks that do both where you live.

 

[Jirkas99]

See if there are rocks that do both where you live.

That is great idea! I will try to find out more about that.I heard some mushrooms do that too. But I haven't tried that.

 

[paul1598419]

I was a rock hound back when I was a kid. I had many fluorescent rocks and minerals. Had to use a black light back then because it was many years before laser diodes and UV LEDs. Some minerals fluoresce, but you have to try to find out which because even the same mineral specimens won't necessarily fluoresce if they came from different areas.

 

[Anthony P]

If you find that interesting, may I suggest a N2 laser build like Scientific American as pump for Dye laser. It is probably the easiest of the gas lasers to DIY and pretty much any color laser is possible with dyes.