Multiphoton Imaging and Ultrafast Spectroscopy Applications

Developed by scientists in Newport’s Technology and Applications Center (TAC), the SF-TRU is engineered to synchronize the two output beams of dual-output laser sources, facilitating a large variety of single- and dual-beam, multiphoton imaging and ultrafast spectroscopy applications, such as:

  • Single- and multi-color (wavelength mixing)
    two-photon fluorescence (TPF)
  • Second harmonic generation (SHG)
  • Third harmonic generation (THG)
  • Coherent anti-Stokes Raman scattering (CARS)
  • Stimulated Raman scattering (SRS)
  • Pump-probe
  • Transient absorption

SRS image of corn stalk in the fingerprint region

CARS and SRS spectroscopy of liquids in the C-H region

The SF-TRU module enables hyperspectral CARS/SRS imaging with spectral resolution up to 5 cm-1. High spectral resolution is achieved by employing spectral focusing with tunable-distance grating pairs, which, in contrast with fixed-length glass rods, allows matching the spectral resolution and the linewidths of the Raman lines of interest. 

(a – c) SRS (green) and CARS (red) spectra of cyclohexane, ethanol and methanol measured by SF-TRU. Chirped pump and Stokes wavelengths are 797 nm and 1041 nm, respectively. The spontaneous Raman spectrum of cyclohexane (black) in (a) shows excellent agreement between spontaneous Raman and SRS spectra. (d) Delay-to-wavenumber calibration curve for hyperspectral imaging obtained from the Raman shift measurements shown in (a – c).

Hyperspectral SRS Imaging in the C-H Region

Top: Hyperspectral SRS images of mixed polymethylmethacrylate (PMMA, large) and polystyrene (PS, small) beads. Two different slices from a stack of a hyperspectral scan are shown. Red and green circles indicate the regions of interest (ROI).

Bottom: SRS spectra of PMMA (red) and PS (green) beads extracted from the hyperspectral scan shown with spontaneous Raman spectrum of PS (black). The vertical bars correspond to the Raman shifts of the frames shown on the top.

Hyperspectral CARS and SRS Imaging in the Fingerprint Region

Top: Hyperspectral CARS (left) and SRS (right) images of polystyrene (PS) beads. Slices from stacks of hyperspectral scans are shown. Chirped pump and Stokes wavelengths are 893 nm and 1041 nm, respectively. Red, green and blue circles indicate the regions of interest (ROI).

Bottom: CARS (red) and SRS (green) spectra of PS beads and CARS spectrum of water (blue) extracted from the hyperspectral scan shown with the spontaneous Raman spectrum of PS (black). The CARS spectra show the non-resonant background inherent to CARS signals in the fingerprint region. The vertical bar corresponds to the Raman shift of the frames shown on the top.

Two-color (Non-Degenerate) TPF Imaging

Two-color (non-degenerate) TPF imaging of a mix of YG and YO fluorescent polystyrene beads: When the two pulses are not temporally overlapped, only the degenerate TPF from the 4.5-micron YO polystyrene beads is observed. This is due to the two-photon interaction from the 1041 nm fixed beam (as checked by blocking the tunable beam). At time zero, the non-degenerate TPF signal from the 2-micron YG polystyrene beads is also activated.

Multimodal Imaging of Microstructures Fabricated by Two-photon Polymerization

Multimodal imaging of a TPP-fabricated microstructure: (a) TPF, (b) CARS, (c) THG, (d) SEM. The insets show the brightest frames of z-stacks.

CARS Imaging of an Optical Fiber

CARS imaging of SMF-28 fiber: (a) z-stack images at z = −20 μm, z = 0 μm, and z = 20 μm, red lines indicate the region of interest, (b) CARS signal versus z, (c) derivative of the CARS signal versus z.

THG Imaging of an Optical Fiber

THG imaging of SMF-28 fiber with 1200 nm excitation: (a) z-stack images at z = 4 μm, z = 34 μm, and z = 65 μm, (b) CARS signal versus z, insets show the schematic diagram and the YZ orthogonal view of the fiber cross section.

SF-TRU Components

Inside the SF-TRU, each beam is equipped with an ultrafast variable attenuator for power control. Additionally, each beam path has a telescope to fill the back aperture of the microscope objective and to focus the two beams in the same focal plane. The fixed-wavelength beam at 1045 nm is passed through a high-precision Newport DL125 motorized delay line stage and a resonant electro-optic amplitude modulator (EOM) for lock-in detection of SRS signal*. Each beam is passed through a grating pair with adjustable dispersion for controlling the chirps. The device allows simple switching from a single- to a dual-beam collinear setup, and from femtosecond to chirped picosecond pulses, without affecting alignment.
* EOM resonant frequency should be specified upon ordering.

SF-TRU Specifications

Technical Specs fs Regime (w/o grating pair) ps Regime (w/ grating pair)

Fixed Beam Wavelength

1045 nm
Tunable Beam Spectral Range (single beam) 680-1300 nm 790-910 nm
Tunable Beam Spectral Range (dual beam) 750-980 nm 790-910 nm
Raman Shift for CARS, SRS 600-3800 cm-1 1300-3200 cm-1
Fixed Beam Pulse Width1 <260 fs 2.2-4.4 ps
Tunable Beam Pulse Width <120 fs 3.5-7.5 ps
Fixed Beam Group Delay Dispersion Range +12,000 fs2 -160,000 to -320,000 fs2
Tunable Beam Group Delay Dispersion Range Provided by DeepSee inside laser
0 to -25,000 fs2 @ 800 nm
0 to -17,000 fs2 @ 900 nm
Provided by gratings
-150,000 to -200,000 fs2 @ 800 nm
-240,000 to -320,000 fs2 @ 900 nm
Raman linewidth for CARS, SRS 145 cm-1 <7 cm-1
Fixed Beam Throughput (pinhole-free silver mirrors)2 >85% Additional 40% loss
Tunable Beam Throughput (dielectric mirrors option) >80% Additional 50% loss
Tunable Beam Throughput (pinhole-free silver mirrors) >70% Additional 50% loss
Attenuation (tunable and fixed beams) 0-2 OD
Output Polarization (tunable and fixed beams)3 S- (vertical) standard
Delay Line Maximum Speed 500 mm/s
Delay Line Travel Range 125 mm
Fixed Beam Modulation Frequency 2-4% range of EOM center frequency specified upon ordering
Beam Entrance Height 4.75 in. (120.7 mm)
Beam Exit Height 4.44 in. (112.7 mm)
Dimensions (LxWxH) 30 x 18 x 7.75 in.
  1. Pulse broadening in the fs regime compared to the laser output (<200 fs) is due to the EOM crystal dispersion.
  2. Specifications only apply to the unmodulated beam. In case of modulated beam, the duty cycle should be taken into account.
  3. Each beam is equipped with a half wave plate to independently control polarizations before exiting the SF-TRU.