Impulse pressure in laser printing with gel microdroplets

Abstract

Laser printing with gel microdroplets containing living organisms is a promising method for microbiology, biotechnology, and medicine. The transfer of small volumes of the gel occurs due to the absorption of a short laser pulse in a thin metal film of the donor plate. During the transfer process, laser printing generates pressure jumps that can cause damage and loss of biological material. Therefore, the assessment of these jumps is important for studying the influence of physical factors on the transferred living systems and improving the technology of laser printing with biomaterials. In the course of laser printing, laser pulses with a wavelength of 1064 nm, energy 7–120 µJ, duration of 4–30 ns with a laser beam diameter of 30 µm were applied to Ti and Cr films of glass donor slides. Experimental estimates of the emerging jumps were carried out on the basis of measurements of the acoustic pressure in the far zone in the range of 1–100 MHz using a hydrophone based on a lithium niobate crystal. It was found that in the operating range of laser energies E = 15–30 μJ in a gel layer with a thickness of 200 μm on the donor plate, pressure jumps from 20 bar to 5 kbar appeared when using an absorbing Ti film and from 20 bar to 10 kbar for a Cr film. The high efficiency of optoacoustic conversion for Cr films is explained by the better adhesion of this metal to the glass surface.