Exemplar ls

Transient absorption spectra of quasi-2D thin films were measured by a home-built femtosecond pump-probe system described in a previous publication^{30 (link)}. Briefly, part of a 1030 nm fundamental Yb:KGW laser (PHAROS, Light Conversion Ltd.) output was focused onto a YAG crystal to generate the broad-band probe, and the rest of the fundamental laser was sent to an optical parametric amplifier (OPA, ORPHEUS-Twins, Light Conversion Ltd.) to generate wavelength tunable pump pulses. An optical chopper (MC200B, Thorlabs) was used to modulate the pump beam with a frequency of 195 Hz. A linear stepper motor stage (Newport) was utilized to delay the probe relative to the pump beam. Both pump and probe beams were focused on the sample with a 5× objective (N.A. = 0.1, Olympus). The pump induced change in the probe transmission was collected by a 20× objective (N.A. = 0.45, Olympus) and detected by an array detector (Exemplar LS, B&W Tek).

The optical emission of the plasma plume was measured by a broadband CCD spectrometer (Exemplar LS; BWTEK Inc., United States). The measured spectrum ranging from 200 to 850 nm was resolved by grating at 600 groove/mm and 25 μm slit width. The light emission from the OH band was detected by a high-resolution spectrometer with 0.05 nm resolution (AvaSpec-ULS3648, Avantes, the Netherlands), and the spectrum ranging from 220 to 340 nm was measured. The experimental configuration is shown in Fig. 1(a). The optical emission collected at about 1.0 cm away from the nozzle. Note that RH in the controlled experimental room was typically 60%.