class3B laser

bear,

Are you referring to something like a Laser pointer? This may answer your questions.....

https://www.tsa.gov/travel/security-screening/whatcanibring/items/laser-pointers

3Bs are more powerful than standard pointer type laser. And they are capable of causing instant eye injury. My guess is that the TSA might have taken a dim view of anything beyond a standard pointer.

actually it is a medical laser unit i use for my shoulder pain relief and knee pain relief

Supposedly (no experience) medical devices are exempted so that might cover you. You may want to carry documentation covering the instrument and the need for it. Good luck --

Note that just because TSA allows it on, doesn't guarantee that foreign countries' security will allow on the return, so you need to consider both.

Laser.....I was thinking a small racing sail boat. Hahaha

And just because the TSA, or any other country's airport security lets it through, does not mean it will get through customs (in the unlikely event you are stopped). It may be classified as an offensive weapon, i.e. it is illegal to carry, same as a knife.

This is the UK info from the Government website. Does nots say whether class 3B is actually illegal or not. It is probably a grey area where if you are carrying it you could be prosecuted: https://www.gov.uk/government/publications/laser-radiation-safety-advice/laser-radiation-safety-advice

This site says "It is now illegal to operate or own lasers class 3b (in some places 3a) or above in almost every country.": https://laserpointerforums.com/threads/actual-laser-laws-by-country.53770/

Chris F has an important point. Bringing it on the plane is one thing, bringing it to another country something different. The rules might be different in different countries, but with a class 3B laser you really should choose the red channel at customs. I just checked the rules in Sweden and a class 3B laser requires permission from the Radiation Safety Authority.

Contact the manufacturer and see if they export to wherever you're going.

Also, check the manufacturing plate of the item. If you see a slightly oversized CE (https://en.wikipedia.org/wiki/CE_marking) then that means it's sold in Europe as well and you're probably ok.

actually it is a medical laser unit i use for my shoulder pain relief and knee pain relief

How is it powered, batteries or is it plugged in?
If the latter, depending on where you live (which country) and which country you are travelling to, you may have the issue of different electrical voltages and/or different plugs.

This summer our granddaughter passed through security screening in SFO with a look and a question about an item she was carrying in her backpack, needle nosed pliers, and was allowed to keep them. On our return trip I thought she’d put them in our checked luggage but she hadn’t so at CDG the security officer pulled her backpack out of the scanner, opened it up, grabbed the pliers, yelled Non at her and tossed them aside. Reiterating that what you take out of one country may not be allowed in or on the plane of another country.