Pharos

Spectrally resolved pump‐probe measurements (presented in Supporting Information) were performed in a non‐degenerate pump‐probe setup based laser system comprised the Light Conversion Pharos laser (wavelength 1024 nm, pulsewidth around 200 fs, average power around 5 W) and Light Conversion Orpheus HP parametric amplifier which provided a tuneable output in the desired spectral range. Measurements were performed in transmission at near‐normal incidence. One of the outputs was routed through a mechanical delay line and chopped at a frequency of 2 kHz. Lock‐in amplification and balanced detection were used to increase the signal‐to‐noise ratio.

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 laser source is a femtosecond laser system (PHAROS, Light Conversion) with a central wavelength of 1028 ± 5 nm and pulse duration ~170 fs. Then, the laser pulses are sent to an optical parameter amplifier (ORPHEUS, Light Conversion) for wavelength conversion. While this offers the possibility to adjust the wavelength, we concentrate here on 1550 nm, the wavelength for maximum conversion efficiency with our system because most studies have been conducted so far in the range 1200-1550 nm corresponding to two-photon absorption initiated interactions in Si. Also, all investigations outside this range have concluded on a relatively modest dependence to the wavelength parameter [22 (link), 38 (link)]. The output energy is controlled by a combination of half-waveplate and polarizer. A parallel grating pair is used to change the pulse duration (from 4 ps to 21 ps). The pulse duration is checked by using a home-built long-scan autocorrelator. Details are discussed in supporting information with the whole setup shown in Figure S1.

The coherent spin dynamics of colloidal QDs were measured using time-resolved ellipticity spectroscopy [11 (link),19 (link),20 (link)]. The experimental configuration depicted in Figure 2 is based on a ytterbium-doped potassium gadolinium tungstate (Yb-KGW) regenerative amplifier (PHAROS, Light Conversion Ltd; the central wavelength is 1026 nm, and the pulse duration is ~270 fs), combined with an optical parametric amplifier (OPA). The laser repetition rates of the OPA outputs are tunable and up to 50 kHz. All the measurements were performed at room temperature and in a transverse external magnetic field provided by an electromagnet with iron poles.
In the pump−probe measurements as shown in Figure 2, the pump and probe pulses are wavelength-degenerate and emitted from the OPA with their wavelength tuned at the low energy side of the first exciton absorption band. The circularly polarized pump pulses generate the spin polarization in the QD samples, while the subsequent dynamics of this spin polarization are monitored by the change of ellipticity of the linearly polarized probe pulses. The linearly polarized probe pulses become partially elliptically polarized after transmitting through the spin-polarized QDs because of the absorption difference of left- and right-circularly polarized light. The time delay between the pump and probe pulses is adjusted by a mechanical delay line.

The TA spectra of the Au NPs, Cu_2–xS NPs and Au@Cu_2–xS NPs were collected using a commercial TA system (HARPIA, Light Conversion). Specifically, a femtosecond laser (repetition rate of 40 kHz, 1030-nm central wavelength and pulse duration of ∼120 fs, PHAROS, Light Conversion) was split into two beams. One beam went through optical parametric amplification (ORPHEUS twins, Light Conversion) to pump the Au@Cu_2–xS NPs. The other beam went through the delay line, which yields the white light via sapphire as the probe beam. The pump and probe beams were focused on Au@Cu_2–xS dispersion in a cuvette with wavelengths of 400 and 640 nm. Single exponential fitting was applied to the TA spectra, which resolves the lifetime of τ.

To determine the optimal laser treatment settings for lithium disilicate glass-ceramics and highly translucent zirconia, an FL (Pharos, Light Conversion Inc., Vilnius, Lithuania) was employed, and the following laser parameters were investigated: (1) Three different peak fluences (F_peak = 2, 4, 8 J/cm²) and four different irradiation numbers (N = 5, 10, 20, 40 shots) were investigated for dot pattern processing; (2) four different peak fluences (F_peak = 2, 4, 8,10 J/cm²) and four equivalent irradiation numbers (N_eq = 5, 10, 20, 40 shots) were investigated for attaining cross-line patterns. The peak fluence is equal to the peak energy irradiated by the Gaussian laser beam, as defined as follows [8 (link)]:
where E is the laser pulse energy and r₀ is the radius of the irradiated beam at 1/e² intensity on the surface of specimens (r₀ = 16.1 µm). The equivalent irradiation number for line scan irradiation, defined as the number of pulses irradiated onto a single point, is given as [9 (link)]:
where f_rep and v_scan denote the laser pulse repetition frequency and the laser beam scanning speed, respectively.

The copper foam was purchased from Kunshan Metal Material Tech., Suzhou, China. The typical line-by-line femtosecond laser irradiation procedure is applied to modify the Cu foam, where detailed information can be found in previous work (Yin et al., 2017b (link); Duan et al., 2018 (link)). In particular, a high-repetition femtosecond laser system (PHAROS, LIGHT CONVERSION, Lithuania) that generates 250 fs pulses at a repetition rate of 75 kHz with a central wavelength of 1,030 nm is employed to fabricate micro/nano structures on the Cu foam surface. The spacing between two adjacent lines is set to be 10 μm. The laser power and speed were set at 8 W and 3 m/s (about 4 s), respectively. After ablation, the samples were carefully cleaned with distilled water.