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J. Eur. Opt. Society-Rapid Publ. 21, 9( 2025)
Figure 1. ISBS microscope setup: PUL excitation laser( 1035 nm, Coherent Monaco); PRL probe laser( 895 nm, DL100 Toptica Photonics); DM dichroic mirror( DMLP650 Thorlabs); COL collimator; L1 to L6 achromatic lenses( AC245-Series Thorlabs); GT grating( custom, grating constant 8 lm); SC sample container( Fused Quartz Cuvettes Thorlabs); ID iris diaphragm; LP long-pass( FEL0850 Thorlabs); DET detector( APD, Femto Berlin); OC oscilloscope.
Figure 2. The dependence of the normalized signal strength in water on( top left) different pulse energies and pulse lengths,( top right) different peak powers and pulse lengths,( bottom left) different pulse energies and repetition rates and( bottom right) different average powers and repetition rates. For the top row the repetition rate was set to 1 kHz and in the bottom row the pulse length was kept constant at 10 ps for all measurements. Arbitrary unit( a. u.).
rate of k = 1 kHz and averaging over N = 1000 measurements. The signal strength increases non-linear with the pulse energy for different pulse length( Fig. 2, top left), making it advantageous to work with high energy pulses, while the pulse length does not seem to influence the signal strength, as the slope for all pulse length is the same. However, the resulting peak power is higher for shorter pulse length and we observed a fluctuation of the peak frequency at around 10 MW for water. We attribute this effect to phototoxicity induced by high peak powers, and consequently, the use of longer pulse length is advantageous for maintaining sample integrity and ensuring reliable measurements. The peak power ^P can be calculated by ^P ΒΌ E p = t p, withE p and t p being the pulse energy and pulse
length respectively. As plotted in the top right of Figure 2, a good parameter choice for a high SNR is a high pulse energy while keeping the pulse length long to reduce the peak power. However, the pulse length must be much shorter than the acoustic period for the excitation to be considered impulsive. It should be noted, that all quantitative limits