What other equipment do I need to consider once I have decided on a Femtosecond Transient Absorption Spectrometer such as Helios?

You would need an excitation light source (laser) and an optical table large enough to accommodate the full set-up. Here are the things you should consider when shopping for a light source:

Pulse energy: It has to be an amplified fs laser capable of producing mJ pulses. Modern Ti-Sapphire amplifiers produce up to 7 W of power (7 mJ/pulse). For Ytterbium-based lasers, we suggest going with 1mJ versions.

Repetition rate: 1 or 2 kHz is recommended. 5 kHz repetition rate is also supported with a higher-speed digitizer option.

Center wavelength: 800 nm or 1030 nm. The tunability of the center wavelength is not important.

Pulse duration: In most cases ca 100 fs pulses are sufficient. These pulses are easier to work with, compared to ca 30 fs pulses. They offer more wavelength excitation selectivity, are more difficult to stretch (narrower spectrum). Also, 100 fs lasers are normally more stable and are less susceptible to temperature and humidity fluctuations in the lab. Basically, you have to have a good reason to go for a ~30 fs laser.

OPA or Harmonics Generator: In many cases, you can get by with a Harmonics Generator, which will give you access to such wavelengths as 400 and 266 nm. If this is not enough for you, you will need an OPA.