Lcpln20xir

We use a pump and probe lateral microscopy setup to measure by free-carrier absorption the characteristics of the microplasmas induced inside silicon with our pump pulses. The experimental arrangement based on a second InGaAs array detector (XENICS, XEVA 1.7-640) is similar to that for the study of the fast kinetics of free-carriers injected in bulk silicon by TPA^{11 (link)}. For microplasma observations, the optical delay between the pump and probe pulses is set at only 10 ps so that we observe the free-carrier distributions before any significant decay^{18 (link)}. For the detection and characterization of permanent modifications in the silicon spheres, the pump is blocked after the illumination. For phase microscopy of the modifications, we rely on a longitudinal-differential interferometry technique^{36 (link)} translated in the infrared domain of the spectrum. Phase images are achieved by using two identical 20×-magnification microscope objectives in both arms of the interferometer (Olympus LCPLN20XIR, NA = 0.45). All experimental details and data are provided in the Supplementary Note 3. For amplitude bright-field imaging we replace the ultrafast probe by a non-coherent infrared illumination (quartz-tungsten halogen lamp) for improved bright-field imaging performance.

The optical system was a standard telecentric beam-scanned spectral-domain (SD)-OCT system (Supplementary Fig. 2a). The SD-OCT system was sourced by a broadband superluminescent diode with a central wavelength of 850 nm and a bandwidth of 120 nm (Superlum, M-T-850-HP-I). Spectral data was detected by a spectrometer with a bandwidth of 180 nm (Wasatch Photonics, Cobra 800) and a 2048-pixel line-scan camera (e2v, Octopus). The sample arm utilized a double-pass illumination/collection configuration with an inverted 20× microscope objective with an NA of 0.45 (Olympus, LCPLN20XIR). Telecentric beam-scanning was accomplished with a 2-axis galvanometer and a zero-magnification telescope, which imaged the galvanometer to the back focal plane of the objective. The illumination beam diameter was ~ 2–3 mm, which under-filled the objective back aperture diameter of 8.1 mm. The native transverse resolution was 2.1 µm at the focal plane and the axial resolution was 1.9 µm in air. The system sensitivity was ~ 90 dB at the implemented acquisition rate (see RE-OCT image acquisition procedure) with a fall-off of − 5 dB/mm. The system was controlled by a custom-built acquisition software in LabVIEW 2014 (https://www.ni.com/en-us/shop/labview.html).

For optical characterization and imaging of microdisks, a laser-scanning LASE microscope modified from a commercial confocal microscope (Olympus FV3000) was used. A pump laser (Spectra Physics VGEN-ISP-POD, 1060–1070 nm, pulse duration 3 ns, repetition rate 2 MHz), with the output power controlled by an acousto-optic modulator and measured by an external photodetector, was coupled to a side port of the laser-scanning unit of the microscope. The day-to-day variation in the measurement of the absolute pump power was up to 30%. The emission from microdisks was collected from the same port and relayed by a dichroic mirror to a NIR spectrometer using an InGaAs linescan camera (Sensor Unlimited 2048 L). A 100 lines/mm grating (0.6-nm resolution over 1150–1600 nm, exposure time: 0.1 ms) was used for threshold characterization, and a 500 lines/mm grating was used for high-resolution linewidth characterization (0.2-nm resolution, 150-nm span, exposure time: 0.1 ms). In both cases, a NIR-optimized, 20X, 0.45-NA objective (Olympus IMS LCPLN20XIR) was used. The high-resolution lasing mapping images were acquired with a 100X, 0.85-NA objective (Olympus IMS LCPLN100XIR) and the NIR spectrometer with the 100 lines/mm grating (0.6-nm resolution over 1150–1600 nm, exposure time: 0.1 ms).

We visualized GCaMP6m-expressing PVT→NAc projection neurons using a two-photon microscope (Bruker Nano Inc) equipped with a tunable InSight DeepSee laser (Spectra Physics, laser set to 920 nm, ~100 fs pulse width), resonant scanning mirrors (~30 Hz framerate), a ×20 air objective (Olympus, LCPLN20XIR, 0.45NA, 8.3 mm working distance), and GaAsP photodetectors. In some cases, two fields of view (FOVs) were visible through the GRIN lens (separated by >75 µm in the Z-axis to avoid signal contamination from chromatic aberration), in which case we recorded from each FOV during separate imaging sessions. Data were acquired without averaging using PrarieView software, converted into hdf5 format, and motion corrected using SIMA⁷³ . Following motion correction, a motion-corrected video and averaged time-series frame were used to draw regions of interest (ROIs) around dynamic and visually distinct cells using the polygon selection tool in FIJI^{74 (link)}. Fluorescent traces for each ROI were then extracted using SIMA, and all subsequent analyses were performed using custom Python codes in Jupyter Notebook^{6 (link),25 (link)}. Two-photon imaging was performed during select acquisition sessions (early: days 1–2; middle: days 7–8; late: days 13–14) and extinction sessions (early: days 1–2; late: last 2 days) to simplify data analysis.