Heavy water detection using ultra-high-Q microcavities

Abstract

Ultra-high-Q optical microcavities $(\mathit{Q}>{10}^7)$ provide one method for distinguishing chemically similar species. Resonators immersed in ${\mathrm{H}}_2\mathrm{O}$ have lower quality factors than those immersed in ${\mathrm{D}}_2\mathrm{O}$ due to the difference in optical absorption. This difference can be used to create a ${\mathrm{D}}_2\mathrm{O}$ detector. This effect is most noticeable at $1300\mathrm{nm}$, where the $\mathit{Q}\left({\mathrm{H}}_2\mathrm{O}\right)$ is ${10}^6$ and the $\mathit{Q}\left({\mathrm{D}}_2\mathrm{O}\right)$ is ${10}^7$. By monitoring Q, concentrations of $0.0001\%$ [1 part in ${10}^6$ per volume] of ${\mathrm{D}}_2\mathrm{O}$ in ${\mathrm{H}}_2\mathrm{O}$ have been detected. This sensitivity represents an order of magnitude improvement over previous techniques. Reversible detection was also demonstrated by cyclic introduction and flushing of ${\mathrm{D}}_2\mathrm{O}$.

© 2006 Optical Society of America