Squeezed light reveals molecules buried in noise

In SRS, the sample produces a stronger signal field than in the linear effect. [...]because the signal field is produced in phase with the Stokes field, constructive interference occurs, greatly boosting the signal from the sample (Fig. 1). In this quantum state, the Stokes photons are no longer fully independent - which means that fluctuations in the number of photons in the beam no longer follow the statistical distribution observed in classical laser beams. Impressive noise reduction has been attained in other techniques by squeezing narrow-band laser light (see ref. 9, for example), but it might prove challenging to achieve similar reductions using the broadband laser beams that are needed for SRS. [...]the process of 'squeezing' light to produce correlations between photons adds an extra step to the already-complicated SRS imaging technique, and might deter users from adopting this noise-reduction approach.