HELIOS FIRE is the next generation, automated femtosecond Transient Absorption Spectrometer in the HELIOS family. Among its numerous advantages, HELIOS FIRE features a 100-fold boost in sensitivity, allowing the study of more delicate samples. This, together with our patent-pending automated beam alignment system, delivers a new level of performance and user-friendliness. In addition to being virtually hands-off, HELIOS FIRE allows for user customization with its easily removable side panels and improved optical layout.


New Features

  • Enhanced sensitivity – compatible with nJ pump energy levels
  • Enhanced beam pointing – drift of <10 µm over the whole delay range
  • Unprecedented degree of automation:
    • Automated optical delay line alignment (Smart Delay LineTM)
    • Automated pump beam alignment
    • Automated switching between UV, VIS and NIR spectral ranges
  • More space around the sample – 225 mm x 250 mm
  • Parabolic reflectors for continuum management ensure uniform focusing of all wavelengths.

More Features

  • 2-unit design with the optical bench isolated from the electronics and detectors. HELIOS FIRE comprises an enclosed optical bench containing all necessary optical and optomechanical components and a 19” rack enclosing all required electronics and a PC. The rack mounted PC contains the necessary data acquisition hardware and software. The optical bench is connected to the rack by a shielded 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. Additionally, such a two-unit design facilitates installation and relocation.
  • 8 ns built-in time window. This is achieved by using a low profile direct-drive ultra-high speed optical delay line. Custom designed mounts are employed 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. Thus the delay line optics are protected from accidental bumping and misalignment.
  • Time window extendable to milliseconds with the EOS add-on.
  • 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 the output power from an OPA (especially in the UV) is low it is necessary to utilize the entire pump beam cross section in order to optimize the data.
  • Optional computer controlled filter wheel for varying pump energy, etc.
  • Magnetically stirred sample holder. Easily interchangeable with optional XY rastering sample holder.
  • Probe Reference. HELIOS FIRE has an option for a second probe (reference) channel. In this variant the probe beam is split into two before passing through the sample. While one arm travels through the sample, the other is sent directly to the reference spectrometer that monitors the fluctuations in the probe beam intensity. The main advantage of this technique is that it allows the user to achieve the specified signal-to-noise ratio with a lower number of averaged laser pulses. This method is primarily used for the experiments with low repetition rate and/or easily photodegradable samples where the number of laser shots is strongly limited.


The HELIOS FIRE data acquisition software has built-in support for the automated alignment of all critical optical elements for largely hands-off operation.  The software is also very user-friendly and versatile:

  • Automated alignment of the optical delay line
  • Automated alignment of the pump beam
  • Computer controlled switching between UV, VIS and NIR modes
  • Supports computer controlled translating sample holder
  • Support pump beam shutter
  • 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 continuum spike rejection- advanced setting which collects data points again if the continuum is not stable.
  • Automatic anisotropy calculation when appropriate optics are used and a reference channel is included.
  • 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 FIRE 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.


  • Fully Automated Optical Delay Line
    • Time window: 8 ns
    • Resolution: 14 fs
    • Minimum step size: 2.8 fs
    • Max. speed: >10 ns/s
    • Acceleration: > 260 ns/s^2
    • Automated alignment time: 3-5 min
    • Beam pointing drift: <10 µm over 8 ns delay range
    • Located inside the spectrometer housing
  • Fully Automated Pump Beam Alignment. The HELIOS FIRE software ensures continuous optimal overlap of the pump and probe beams in a sample with <10 µm precision.
  • Temporal Resolution. The instrument response function is a cross-correlation of the pump and probe pulses. See the optical delay line description for more details.
  • Probe spectral range
    • 320-750 nm
    • 420-800 nm
    • 800-1600 nm
  • Spectral Resolution
    • Intrinsic spectral resolution:
      • VIS – 2 nm
      • NIR – 5 nm
    • Spectral resolution with a 200 µm slit (recommended):
      • VIS – 4 nm
      • NIR – 13 nm
  • Detectors
    • VIS. Custom designed fiber-coupled alignment-free spectrometer with a 1024 pixel CMOS sensor (spectral response: 200-1000 nm). Typical spectral range spans 600 nm (ie. 350-950 nm).  Spectral acquisition rate – up to 5000 spectra/s. ADC resolution – 16 bit. Mounted in a 19″ rack outside of the optical bench.
    • NIR. Custom designed fiber-coupled alignment-free spectrometer with a 256 pixel InGaAs sensor (spectral response: 800-1600 nm). Typical spectral range spans 800 nm (ie. 800-1600 nm). Spectral acquisition rate – up to 5000 spectra/s. ADC resolution – 16 bit. Mounted in a 19″ rack outside of the optical bench.
  • Dimensions
    • Optical bench:  W24” x L36” x H10” (W610 x L915 x H250 mm)
    • Electronics rack:   W21” x L24” x H27” (W534 x L610 x H686 mm)


Some research areas where HELIOS FIRE is useful are :

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

Helios owners are using the instrument in a variety of projects, some of which are listed below.
More detail can be found under the Selected Publications tab on this page.

  • Photo-processes on single wall carbon nanotubes
  • Photophysical properties of two-photon chromophores
  • Non-linear absorbing platinum complexes
  • Non-radiative transitions and excited state dynamics
  • Blinking in silver nanodot fluorescence
  • Acoustic vibrations in gold nanoparticles
  • Material properties of metal nanoparticles
  • Photochemistry of cadmium selenide quantum dots
  • Non-linear absorption of PbS nanoparticles
  • Non-linear absorption and optical limiting in the near infrared
  • Methanofullerene cations on polymer solar cells
  • Supramolecular conglomerates of phthalocyanines and porphyrins
  • Photoprocesses in triads of fullerene and phthalocyanine
  • Plasmon damping in colloidal metallic nanoparticles
  • Surface plasmon resonance of metal nanoparticles
  • Infrared photon harvesting using dye clusters
  • Femtosecond spectrometry of lobster pigments
  • Geometric isomers of carotenoids
  • Quantum Confinement in Optically Excited Gold Clusters
  • Optical Excitations in Supramolecular Metallocycles
  • Electronic Properties of Oligoenes and Oligothiophenes
  • Ultrafast Polaron and Triplet Exciton Formation in Polythiophene Films
  • Photo-induced Electron Transfer in Ruthenium(II)/Tin(IV) Multiporphyrin Arrays
  • Photo-induced Processes in Metallo­-supramolecular Boxes
  • Multilayers of Terpyridine-functionalized Perylene Bisimide Metal Complexes
  • Photo-induced energy transfer in a rod-like dinuclear Ru(II) complex
  • Photo-induced Processes in Porphyrin-Perylenebisimide Symmetric Triads