CO2 5-10
A DIY laser built from scratch, using a balloon and needle valve to supply gas to an electrical discharge. The laser will run on a mixture of helium, CO2, and nitrogen, or it will run on ordinary exhaled breath! Helium only enhances laser performance. CO2 and nitrogen are the only two gasses that are absolutely required. The laser will run with air that is simply exhaled into a balloon, because there is both nitrogen and CO2 present in the air that we exhale. In order to do so, I hold my breath before exhaling into the balloon, allowing my body to replace more oxygen with CO2 than would occur if done quickly.

If I'm using an actual gas supply as opposed to just running the laser on my breath, I first deposit a small amount of CO2 into the storage balloon (hereafter abbreviated as SB). I measure the circumference of the SB using a tailors measuring tape, and then use this circumference to calculate it's volume. After considering the volume of CO2 that the SB contains (I want the CO2 to be about 10% of the final mix), I decide how much N2 I want in the mix. If I want roughly twice as much N2 as CO2 in the final mix, then I add this corresponding volume to the volume of CO2, and calculate a new circumference (in other words, 3x the volume of CO2, which I originally calculated). I then fill the SB with N2, until I arrive at this new circumference. At this point, I divide the sum of the two volumes by 30% (assuming I have twice as much N2 as CO2), and then calculate a final circumference using this number. Following this last step, I inflate the balloon with helium until this final circumference is reached. In this way, the 3 gasses can be combined in a predetermined ratio with some accuracy. Sure - the balloon is not a perfect sphere, but this method is much more accurate than simply guessing!

Helium can be obtained at Walmart in the form of a party balloon kit - cost around \$20. Air should be fine for nitrogen, although welding nitrogen would probably be better if available. CO2 can be obtained from dry ice, or by mixing baking soda and vinegar.

Please check out my other homemade-laser videos, which include other laser types I have built: