Set-up

The experimental setup is shown in Fig. 1c. Jets are actuated by a 5-ns laser pulse (Continuum, ML-II, 532 nm) focused by a 20x microscope objective on a liquid filled borosilicate glass capillary with inner diameters 300, 150 and 100 μm (CM Scientific Ltd.) for generation of the jets of 30, 15 and 10 µm respectively. The distance between the meniscus interface and laser focus Z was kept twice the capillary diameter, which we found as a minimum for having a jet with the same direction as the capillary axis. To prevent breakage of capillaries due to the optical pulse or generated pressure, we use a thick wall capillary with the outer diameter of 3 mm. The meniscus position in the capillary is controlled by a custom-made syringe based pump in case of single shot experiments. For jetting in repetitive regime, we use the Syringe pump (New Era Pump Systems Inc., NE-1000) with customizable flow rates. Capillaries are tightly sealed to the syringe connector without tube connectors to minimize flow rate settling time. To monitor the optical energy, we split the pulse by the polarization beam splitter (PBS) where the splitting ratio is given by the polarization angle adjusted with a half-wave plate (λ2), measurement is done by a power meter (Thorlabs, ES111C). The imaging of the jet formation, jet speed and transparent material penetration is performed with an ultra-fast camera (Vision Research, Phantom Miro M310), which requires a back illumination of the scene to obtain a good contrast image (custom-made high brightness source). The minimum time between two frames in our experiments is 5 µs (200 kfps). For the velocity measurement we use the objective with the magnification 2×, 4×, 6× for measurement of 30, 15, 10 µm jets respectively. Synchronization of the laser and the camera is performed by the delay generator (Berkley Nucleonics, Model 577). To enhance the laser light absorption at the wavelength of pulsed light source (532 nm), we stained the liquid with 52 mM of Allura Red AC (ARAC; 80%, Sigma Aldrich, USA). The absorption coefficient of the solution was measured as ϵ=70⋅103m−1. The standoff distance between hydrogel substrate and the initial meniscus is kept constant at 1.5 mm, which is still within the range where the jet keeps its asymptotic velocity²¹ and does not undergo significant deceleration.