If you're a US citizen with no criminal record, try defense contractors (Raytheon, Northrop Grumman, etc.), national labs, DoE internships, the Army, Air Force or Navy (look for "Physical Science Technician") and other jobs in government institutions (environmental protection, meteorological institutions, natural science bureaus like the Geological Survey).
Private sector: optics companies/manufacturers(Thorlabs, OFSOptics, etc.), renewable energy companies, power plants, start-up high tech, entry level banking or programming positions (if you have demonstrable programming skills in java, c++, etc.)
I have had more luck finding ads by specifically seeking out companies' career pages than scouring job ad pages like USAjobs and monster.
But having contacts through your university's services is really what is most likely to land you any job than looking and applying online + cold-calling on your own. Strong-arm your university career services office and attend any job fairs they hold.