You are right to be thinking of safety. I offer the following observations:
A safety switch shouldn't rely on a spring to driven into the off position when the guarding is open. That way if the switch spring fails then the system fails in a safe mode. This often relies on the use of a cam or similar mechanism to operate the switch. Safety-rated magnetic switches are also available but these are probably out of budget for your application.
The problem with the solid state relay is that you can't predict its failure mode. If the switching element fails it is as likely to fail short-circuit as open-circuit. Mechanical relays are much more reliable in this regard and their major risk is contact welding but this can be mitigated by using a high safety factor in the contact rating.
Industrial safety circuits use redundant circuits: the safety switch will have two contacts and drive two relays in a supervisory unit. Both relays must drop out before the system can be reset. (That way you catch the first fault if a switch or relay fails.)
- Use forced disconnect when the guard is open.
- Use an over-specified relay or two.
- See if you can add a supervisory circuit to alarm if the relay doesn't match the switch position.
- Add an indicator LED (bright) to indicate when the laser is powered. After a while you'll get used to the LED turning off when the guard is opened to the extent that you should recognize a fault if it occurs.
I have described the operation of a safety relay in my answer to Symbol or marking on safety relay. You might find it of interest.