Stimulated Raman Scattering (SRS)
Stimulated Raman Scattering (SRS) microscopy for non-
Coherent Anti-Stokes Raman Spectroscopy (CARS)
CARS Coherent anti-Stokes Raman Spectroscopy (as well as Stimulated Raman Scattering) create high imaging contrast without labeling. The technology involves two laser beams. CARS is sensitive to the vibrational modes of samples and visualizes the vibrational contrast of molecules. The samples, even living objects, remain almost unaffected.
SRS Microscopy and CARS Spectroscopy with a Tunable ps Two-Color Laser
CARS & SRS in a Single-box
SRS Stimulated Raman Scattering microscopy and CARS Coherent Anti-Stokes Raman Spectroscopy have migrated from physics labs to life-science labs, so APE has responded with an easy-to-use and truly hands-off SRS and CARS light source: picoEmerald. In a single-box, picoEmerald provides fully automated temporal- and spatial-overlapping ultra-short pulse trains: 1032 nm from the laser oscillator, plus the OPO Signal beam, and OPO Idler beam. The picoEmerald is software configurable to emit the following beam combinations at its output port: (1) Signal and 1032 nm; (2) Signal and Idler; (3) Signal, Idler, and 1032 nm.
Turning Complexity into a Turn-Key System
The light source is the most crucial and complex component of a SRS or CARS microscopy system. Proper setup and calibration are essential for accurate and reproducible imaging. picoEmerald is a turn-key system combining user-friendly automation features and the utility of open-architecture light sources in a single box.
- Stimulated Raman Spectroscopy (SRS)
- Coherent Anti-Stokes Raman Spectroscopy (CARS)
- SRS Microscopy of Vibrational Probes
- Second Harmonics Imaging (SHG)
- Pump-Probe Spectroscopy
- Surface Enhanced Hyper Raman Spectroscopy (SEHRS)
Setup and Use with Microscopes
picoEmerald is compatible with nearly all popular confocal microscope systems. The current publication list names at least those configurations:
- Home-built setups
- Leica SP-Series
- Olympus FV-Series
- Nikon Ti-U Platform
- Thorlabs Multiphoton
- Zeiss LSM-Series
By integrating SRS and CARS technology into Leica’s confocal SP5/SP8 microscopy system, Leica Microsystems has tightly integrated the picoEmerald into their LAS AF system software. Similary tight software integration is also available with Thorlabs’ multi-photon microscopes. Software integration into other third-party microscopes or home-built setups is also supported. Ethernet TCP/IP and serial RS232 interfaces are available with picoEmerald for this purpose. APE’s user-friendly automation combined with a graphical user interface (GUI) also makes it convenient when using picoEmerald and microscope as independent instruments, without the need for software integration.
Introduction to Stimulated Raman
Stimulated Raman Scattering (SRS) is based on the effect that excited molecules emit spontaneous Raman scattering, SRS is a further development of CARS. In the event of two different laser beams with a frequency difference which matches the vibrational frequency, the Raman signal will be amplified. So this process is not spontaneously anymore, it is stimulated.
This technique requires two laser beams. A Pump and a Stokes beam. One of these beams must be tuneable in order to meet the difference of the frequencies, so that the molecules can be excited into the virtual state and to bring it to the vibrational state. As at CARS, the molecules are only excited if the frequency coincides with the vibrational resonance.
The tuneable Pump beam gets a loss in intensity after excitation of the molecules (stimulated Raman loss – SRL). On the opposite, the intensity of the non-tuneable Stokes beam increases (stimulated Raman gain – SRG).
The different intensities between input Pump beam and output Pump beam are very low. So low, that the true measurement signal is lost in the noise. To measure this difference, the lock-in technique is used. For this the Stokes beam is modulated to a fixed frequency by an Electro-Optical Modulator (EOM). APE has integrated such EOM into picoEmerald.
Unlike CARS, SRS provides results with no non-resonant background. The assignments of CARS spectra are more complicated and thus the interpretation is more susceptible to errors. SRS is based on spontaneously Raman scattering and so the obtained SRS spectra are almost identical with spectra of spontaneously Raman scattering. Furthermore, SRS signal is directly linearly dependent to the concentration.
|Wavelength 1 (Stokes)||1032 nm ± 1.5 nm|
|Wavelength 2 (Pump - Signal)||700 nm … 990 nm|
|Wavelength 3 (Idler)||1080 nm … 1950 nm|
|Power 1 (Stokes)||>700 mW unmodulated|
|Power 2 (Pump - Signal)||>700 mW at 800 nm|
|Power 3 (Idler)||>400 mW at 1250 nm|
|∆v Pump - Stokes||400 cm-1 … 4500 cm-1|
|∆v Pump - Idler||800 cm-1 … 9000 cm-1|
|Spectral bandwidth||~10 cm-1 (Pump - Signal and Stokes)|
|Pulse width||~2 ps (Pump - Signal and Stokes)|
|Repetition rate||80 MHz ± 0.5 MHz|
|Noise||Shot noise limited (-161 dBc/Hz) >10 MHz for Pump - Signal|
|Pointing stability||<100 µrad per 100 nm
(typical 100 µrad over entire range)
|M2||<1.2 for Pump - Signal, typical 1.2 for Stokes|
|Polarization||Linear, horizontal >100:1|
|Beam divergence||1.0 mrad ± 0.2 mrad at 800 nm and Stokes|
|Beam waist diameter||1.2 mm ± 0.2 mm at 800 nm, 1.7 mm ± 0.2 mm for Stokes|
|Software configurable output modes||1. Signal and 1032 nm, or
2. Signal and Idler, or
3. Signal, Idler and 1032 nm
respectively with overlap in space and time
|Wavelength measurement||Integrated spectrometer for Pump - Signal wavelength|
|Power attenuators||Integrated for Pump - Signal and Stokes, indepedent for each beam|
|Wavelength sweep function||Start/End function, user-defined holding time, trigger function
Max. step size: 2 nm
Tuning speed: ~5 s per wavelength step
|Remote control||Possible via USB, Ethernet TCP/IP or RS232|
|SRS modulator||EOM with resonant fixed modulation frequency of 20 MHz
Built-in and controllable with the same software
1032 nm beam modualted power: 300 mW
|High power for 1032 nm beam||2 W (unmodulated), 1 W (modulated)|
|Long pulse / Narrow-bandwidth option||~4.5 ps / ~5 cm-1 Pump - Signal
~6.5 ps / ~10 cm-1 Stokes
|Additional IR output port||Additional 1032 nm beam output for pumping another OPO (Levante IR ps)
Wavelength: 1032 nm ± 1.5 nm
Power: >4 W
Spectral bandwidth: ~10 cm-1
Pulse width: ~2 ps (~6.5 ps optional)
Repetition rate: 80 MHz ± 0.5 MHz
- Stimulated Raman Scattering + Coherent Anti-Stokes Raman Spectroscopy with one device
- Automated optical delay management to compensation for microscope dispersion
- Wavelength scan / sweep function for fast spectra acquisition
- Independent power control for 1032 nm beam and Signal beam
- Remote-service via LAN interface
- Optional: Wavelength extension from 210 nm – 10 μm
(Realized by SHG, THG, FHG, or DFG; e.g. APE’s HarmoniXX)
Above: Typical Signal and Idler power vs. wavelength
Above: Relative intensity noise (RIN): Shot noise limited OPO Signal output for frequencies > 10 MHz
Email & Phone Contacts
APE has distributors around the world to give you the best support. Choose a country to find your local sales contact:
Turning Complexity into a Turn-Key System
The light source is the most crucial and complex component of a CARS Coherent Anti-Stokes Raman Spectroscopy or SRS Stimulated Raman Scattering system. Proper setup and calibration are essential for accurate and reproducible imaging. picoEmerald is a turn-key system combining user-friendly automation features and the utility of open-architecture light sources in a single box.