  Raman-based technologies have enabled many ground-breaking scientific
discoveries related to surface science, single molecule chemistry and biology.
For example, researchers have identified surface bound molecules by their Raman
vibrational modes and demonstrated polarization-dependent Raman gain. However,
a surface constrained Raman laser has yet to be demonstrated because of the
challenges associated with achieving a sufficiently high photon population
located at a surface to transition from spontaneous to stimulated Raman
scattering. Here, advances in surface chemistry and in integrated photonics are
combined to demonstrate lasing based on surface stimulated Raman scattering
(SSRS). By creating an oriented, constrained Si-O-Si monolayer on the surface
of integrated silica optical microresonators, the requisite conditions for SSRS
are achieved with low threshold powers (200microW). The expected
polarization-dependence of the SSRS due to the orientation of the Si-O-Si bond
is observed. Due to the ordered monolayer, the Raman lasing efficiency is
improved from ~5% to over 40%.
