| 356 / | HD | OPTICS: MEASURING AND TESTING |
| 928 | DD | INVESTIGATING OR ANALYZING MATERIALS BY THE USE OF OPTICAL MEANS, I.E., USING INFRA-RED, VISIBLE, OR ULTRA-VIOLET LIGHT (GO1N 21/00) {5} |
| 931 | DD | .~ Systems in which incident light is modified in accordance with the properties of material investigated (GO1N 21/17) {8} |
| 932 | | .~.~ With opto-acoustic detection, e.g., for gases or analyzing solids (GO1N 21/17B) |