Enhanced Strain Sensitivity: The ability to measure tiny deformations in length is useful for many disciplines, from largescale structural engineering to DNA analysis with optical tweezers. The most sensitive strain sensors are those using optical interferometers, which can detect small changes at the scale of visible wavelengths. Using an optical frequency comb to stabilize the output of a diode laser, and as a highly accurate ruler to determine small changes in length of an optic fiber sensor, Gagliardi et al. (p. 1081 , published online 28 October) showed that sensitivity can be enhanced by several orders of magnitude. Such combined technology should provide for a new generation of high-performance sensors.

A novel diode laser spectrometer was developed using dual-wavelength multiplexing, ensuring ideal conditions for high-precision and simultaneous measurements of the ²H/¹H, ¹⁷O/¹⁶O, and ¹⁸O/¹⁶O isotope ratios in water. A 1.4-µm diode laser probed a H¹⁶OH / HO²H line pair near 7198 cm^-1, while a similar laser observed H¹⁶OH, H¹⁷OH, and H¹⁸OH ro-vibrational lines around 7183 cm^-1, or a H¹⁶OH / H¹⁸OH line pair near 7200 cm^-1. The 1-σ standard deviation is 0.2‰ for ¹⁸O/¹⁶O, and 0.5‰ for the ²H/¹H and ¹⁷O/¹⁶O isotope ratios. Preliminary experiments with repeated injections of a natural abundance sample point to an accuracy of about 1‰ for all three isotope ratios in natural samples.