HELIOS IR is a broadband mid-infrared pump-probe femtosecond Transient Absorption Spectrometer. A complete turnkey system, HELIOS IR comprises an enclosed optical bench containing all necessary optical and optomechanical components and a 19” rack enclosing all required electronics and a PC. The optical bench is sealed for purging with dry gas and is connected to the rack by an umbilical cord. This architecture allows keeping all regularly accessed parts of the system within reach, while protecting and consolidating all auxiliary components in a steel rack. A rack mounted PC contains the necessary data acquisition hardware and software. Top quality hardware components from Hamamatsu, JY Horiba, ThorLabs, Newport, CVI and other industry leaders ensure high reliability and longevity of HELIOS IR and all our other spectrometers. HELIOS IR is designed to work with standard femtosecond infrared light sources (OPA). The spectrometer comes with advanced data analysis software, SURFACE XPLORER, capable of various types of data processing including Global Analysis. With its broad spectral coverage and a long time window, HELIOS IR will produce superb spectral and kinetic data needed for your investigations of photoexcitation events with ultrafast time resolution.



  • 2-unit design with the optical bench isolated from the electronics.
  • Advanced user-friendly LabVIEW based software for instrument control and data acquisition.
  • Broad probe spectral range: 2-13 µm.
  • 8 ns time window. We achieve it using a low profile direct-drive ultra-high speed optical delay line. We use custom designed mounts for the delay line optics to increase the beam alignment reproducibility and the overall reliability. This delay line features high resolution as well as very high speed. Scanning at high speeds is very important because it allows for pseudo-random stepping without a significant increase in the experiment time. This type of stepping is very useful for minimizing the effects of laser instability and sample degradation. The delay line is integrated inside the Helios optical bench. This keeps the delay line optics protected from accidental bumping and misalignment. To ensure perfect alignment of the delay line we use a beam profiler for computer assisted control.
  • Support for large pump beam diameters. The proprietary design of our fully enclosed optical chopper accommodates pump beams of up to 9 mm in diameter without sacrificing the contrast of pump-on and pump-off measurements and the transient absorption signal amplitude. This is important because when you don’t have much power out of an OPA (especially in the UV) you cannot afford putting an iris in front of a chopper. In such cases being able to utilize the whole pump beam cross section is critical for getting good data.
  • Reflective Optics Probe Routing. Helios IR utilizes reflective optics to minimize the focal plane shift when switching probe wavelengths. This ensures a more hands-off operation, which is very important since the probe is invisible.
  • Optional computer controlled filter wheel for varying pump energy, etc.
  • All electronics are enclosed in a separate electronics rack connected to the main Helios IR unit by a protected umbilical cable.
  • When configured with a dual array detection Helios IR has an option for a second probe (reference) channel. In this mode the probe beam is split into two before passing through the sample. While one leg travels through the sample, the other is sent directly through a spectrograph onto a reference MCT detector array. The reference channel thus allows for correcting the fluctuations in the probe light. Since most signals in the Mid-IR are small and the probe light is generated through several non-linear transformations in an OPA correcting for an OPA output instabilities greatly improves the S/N ratio in the data.


HELIOS IR features versatile and user-friendly LabVIEW based software for instrument control and data acquisition. The software allows for experiment automation, such as preset optical delay step sizes, averaging time for each transient spectrum, time window. Alternatively user can adjust the above parameters during the data collection process. Random delay line stepping is available for the above regimes.

  • Supports computer controlled translating sample holder
  • Support pump beam shutter for increased automation.
  • Supports motorized filter wheel for automated pump intensity control.
  • Saves every individual kinetic scan, so if experiment is aborted (due to laser fluctuations, power outages, etc.), all previous scans are not lost.
  • Threshold adjusted automatic probe intensity spike rejection- advanced setting which collects data points again if the continuum is not stable.
  • Two levels of user access – basic (default, most commonly used settings), advanced (allows to change DAQ parameters, such as continuum stability thresholds, digitizer dynamic range, etc.)
  • Support for multiple choppers to facilitate customized experiments, such as “pump-pump-probe”, “pump-dump-probe” or experiments where the probe beam is also modulated.
  • API (Application Programming Interface) for Helios IR is provided for further experiment customization and integration with external applications. For example, studying temperature dependence on the kinetics with a computer controlled cryostat, etc. can be easily automated through the API. Another example is integration of a computer controlled ND filter wheel or an OPA to perform multiple kinetic scans at different excitation energies or wavelengths.
  • Data format. The Helios software produces a 3-Dimensional Wavelength-Time-Absorbance data matrix in a form of a .ufs file , which can be easily exported into ASCII with Surface Xplorer.


  • Low profile direct-drive ultra-high speed optical delay line integrated in the spectrometer housing.
    • Time window: 8 ns
    • Resolution: 14 fs
    • Minimum step size: 2.8 fs
    • Max. speed: >10 ns/s
    • Acceleration: > 260 ns/s^2
  • Temporal Resolution. The instrument response function is a cross-correlation of the pump and probe pulses. The typical HELIOS IR IRF is 1.4 times longer than the laser’s fundamental pulse duration. See the optical delay line description for more details.
  • Probe spectral range.
    • 2-13 µm
  • Spectral Resolution. Helios-IR spectrometer comes standard with three gratings to allow for different detection bandwidths and spectral resolution. The system comes standard with the following gratings:
    • 3-9 µm, 0.4 µm bandwidth with 6.2 nm resolution
    • 4-10 µm, 0.8 µm bandwidth 12.4 nm resolution
    • 3-9 µm, 1.2 µm bandwidth 18.6 nm resolution
  • Detectors. Helios-IR can be configured with a several MCT array detector options, with larger arrays for broader detection bandwidth or higher spectral resolution and dual array detectors for reference detection.
    • 32, 64 and 128 element single array
    • 16×2, 32×2 and 64×2 element dual array (recommended)
  • Dimensions
    • Optical bench:      W34” x L56” x H14” (W864 x L1425 x H356mm)
    • Electronics rack:   W21” x L24” x H27” (W534 x L610 x H686 mm)


Helios IR can be used to monitor photoinduced species absorbing in the mid-infrared spectral region. For example, vibrationally excited states, charge carriers and electronically excited states in low band gap nanomaterials, etc.

Some research areas where Helios IR is useful are :

  • Photophysics
  • Photochemistry
  • Photobiology
  • Cell biology
  • Materials science
  • Nanoscience
  • Transient spectrometry, and many more areas.

Selected Publications

Data Examples

For data examples please visit our Apps Lab page.