{"id":15814,"date":"2024-01-16T23:59:06","date_gmt":"2024-01-16T23:59:06","guid":{"rendered":"https:\/\/liquidinstruments.com\/?p=15814"},"modified":"2025-12-18T04:23:27","modified_gmt":"2025-12-18T04:23:27","slug":"srs-lock-in-amplifier","status":"publish","type":"post","link":"https:\/\/liquidinstruments.com\/blog\/srs-lock-in-amplifier\/","title":{"rendered":"Stimulated Raman scattering (SRS) with a lock-in amplifier","gt_translate_keys":[{"key":"rendered","format":"text"}]},"content":{"rendered":"

Stimulated Raman scattering (SRS), also known as stimulated Raman spectroscopy, is a widely used technique for label-free chemical imaging that leverages the <\/span>coherent Raman scattering<\/span><\/a> process. While the spontaneous Raman effect is a weak scattering process that can take hours of signal integration time for a single field of view, coherent scattering methods like SRS provide a non-destructive, label-free technique.<\/span>1<\/sup><\/span> Lock-in amplifiers<\/a>, namely specialized SRS lock-in amplifiers, play a critical role in SRS microscopy by performing phase-sensitive detection to extract weak SRS signals from noisy backgrounds.<\/span><\/p>\n

How does stimulated Raman scattering (SRS) work?<\/strong><\/h2>\n

Basic principles<\/span><\/h3>\n

The SRS technique uses two synchronized pulsed lasers \u2014 the pump and Stokes beams \u2014 to coherently excite the vibrational modes of molecules within a sample. When the frequency difference between the two lasers matches the vibrational frequency of the target sample, the pump beam loses photons, a phenomenon known as stimulated Raman loss (SRL), while the Stokes beam gains photons. The intensity loss in the pump beam is incredibly small and requires a lock-in amplifier in order to be detected. Using a high-frequency modulation and phase-sensitive detection scheme with a specialized SRS lock-in amplifier can help extract these signals from noisy backgrounds.2<\/sup><\/span><\/p>\n

Researchers can further enhance their setups by using multi-instrument SRS lock-in amplifier technologies, where additional lasers and lock-in amplifiers enable imaging of different spectral regions simultaneously (Figure 1), which is particularly useful for live cell imaging and other time-sensitive experiments.<\/span><\/p>\n

\"Lock-in<\/p>\n

Figure 1: Simultaneous two-channel SRS images of murine brain samples at two different Rama transitions (2850 cm<\/span>-1<\/span> lipid, left; 2930 cm<\/span>-1<\/span> protein, right)<\/span>2<\/sup><\/span><\/p>\n

The fundamentals of an SRS lock-in amplifier<\/span><\/h3>\n

Lock-in amplifiers are especially well suited for SRS since they allow scientists to amplify signals at a specific modulation frequency, namely that of the pump or Stokes beams. This approach increases the sensitivity of the measurements when measuring signal amplitude and signal phase, since lock-in amplifiers can detect the desired signal, which is in-phase with the reference signal, while rejecting out-of-phase components. Lock-in amplifiers for SRS should also contain digital filters to filter out noise and attenuate unwanted signals to enhance the signal-to-noise ratio of the measurement.<\/span><\/p>\n

What functions do SRS lock-in amplifiers enable?<\/strong><\/h4>\n