HELIOS Femtosecond Transient Absorption Spectrometer by Ultrafast Systems

Overview of the HELIOS Femtosecond Transient Absorption Spectrometer by Ultrafast Systems

https://ultrafast.systems/products/sp...

HELIOS is an automated femtosecond Transient Absorption Spectrometer designed to work with various amplified femtosecond lasers, including high-energy Ti:Sapphire amplifiers and high repetition rate Yb amplifiers. Together with our patented optical delay line, HELIOS delivers an unmatched level of performance and user-friendliness.

• Probe Spectral Range: UV-VIS-NIR-SWIR
• Large Sample Area
• Extendable Time Window
• Automated
• Microscopy Extensions

Spectral Resolution Optimized for Transient Absorption:
For transient absorption, a higher spectral resolution is not always better. It is important to map out all the spectral features, but delivering enough probe light to each detector pixel is also critical. These two parameters counteract - with not enough probe light the data can be noisy; and with not enough spectral resolution some important features can be missed. Therefore, we configure the spectral resolution to be sufficient for resolving what is practical in condensed-phase experiments but not excessively high to allow for enough probe light on the detector.

8 ns time window. Extendable to ms:
The nanosecond window is achieved by using a direct-drive high-speed optical delay line. Custom-designed mounts are employed for the delay line optics to increase the beam alignment reproducibility and overall reliability. This delay line features high resolution as well as 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.

FastScan:
FastScan is a cutting-edge technique that greatly improves the data collection efficiency in transient absorption.

With FastScan, transient spectra are collected continuously as the delay line moves down the track. This means every laser pulse is registered as the data collection does not pause for the delay stage to move from one time point to another.

This technique offers several significant advantages:

The data acquisition time is shortened significantly, especially at the higher laser rep rates. Even at 1 kHz, the data collection is ~3 times faster with FastScan.
With easily photodegradable samples, you can get a quick preview of the full dynamic surface in just seconds before committing to running a full experiment.
Since each delay scan only takes seconds, it is much easier to catch the moment when something goes wrong and still save the good data. For example, if your sample starts to degrade, etc.
Since many more time scans are averaged to get the final dynamic surface, things like pump noise get averaged out much better so your resulting kinetic traces are cleaner and more reliable.

Reflective probe light management
We use off-axis parabolic reflectors to collimate and focus the probe light in Helios. This results in a ~50 µm probe beam waist at the sample. Focusing the probe beam tightly allows to use low energy excitation, down to tens of nJ/pulse, without sacrificing signal amplitudes.

Built-in automation
• Automated optical delay line alignment (Smart Delay LineTM).
• Automated switching between UV, VIS, NIR, and SWIR spectral ranges.
• Automated Pump Beam Alignment.
• Also, using reflective optics in the probe path improves the time resolution of the setup.

Detectors:
All Helios detectors are fiber-coupled spectrographs with linear array detectors. Each spectrograph has an aberration-corrected concave grating for maximum light throughput (essential for high-quality data). The ADC resolution is up to 16-bit. All detectors are mounted in a 19” electronics rack outside the optical bench.