Fig. 1. Liquid thin films produced by three different methods. (a) Gravity driving^[15]; (b) jetting^[21]; (c) jet collisions^[22]

Fig. 2. Terahertz waves and related curves generated by water film at different positions. (a) Terahertz waves generated by water films at different locations^[10]; (b) curves A-C correspond to the terahertz wave signals generated at different water film positions on the left, and curve D corresponds to the terahertz wave signals generated by the air plasma^[10]; (c) comparison of terahertz wave frequency spectra generated by liquid water and air plasma^[23]

Fig. 3. Liquid water columns. (a) Liquid water columns produced by syringe needles^[24]; (b) fluid circulation systems^[5]

Fig. 4. Schematic diagram of the experimental setup, illustration shows schematic diagram of the interaction of laser with the position of the water column^[15]

Fig. 5. The results of laser excitation of water column, water film, and air to produce terahertz waves^[15]. (a)‒(c) Time domain waveforms of terahertz waves generated by water column, water film, and air plasma; (d) spectrogram

Fig. 6. Terahertz waves generated by liquid nitrogen^[26]. (a) Schematic diagram of the device guiding the liquid nitrogen column; (b) photographs of columns of liquid nitrogen flowing in the environment; (c) comparison of terahertz waveforms produced by water (red line) and liquid nitrogen (black line) under the same excitation conditions, illustrated with the corresponding spectra

Fig. 7. Terahertz waves generated by liquid gallium^[27]. (a) System diagram; (b) comparative plot of terahertz waves generated by air, water and liquid gallium, respectively; (c) the solid line represents the normalized terahertz wave field, the dashed line represents the corresponding location where the terahertz wave peak is generated, and the gray area represents the diameter of the water column

Fig. 8. Schematic diagram of liquid water detection system^[28]

Fig. 9. Relationship between second harmonic intensity and detected light energy in air and water plasma supercontinuum radiation^[1]. (a) Air plasma; (b) water plasma

Fig. 10. terahertz wave coherent detection based on liquid water^[29]. (a) Schematic diagram of experimental setup; (b)(c) measured terahertz time domain waveform and spectrum

Fig. 11. The relationship between TISH energy and relative polarization angle. (a) The relationship between TISH energy and relative polarization angle in the absence of CSH, where the cross and dotted lines correspond to vertical and horizontal components, respectively; (b) the relationship between TISH energy and relative polarization angle in the presence of CSH

Fig. 12. Second harmonic radiation of plasma in air and liquid water under single-pulse laser excitation

Fig. 13. Terahertz time domain waveforms for detection of different solutes aqueous solutions^[47].(a) Iodide (cesium iodide, lithium iodide, sodium iodide, potassium iodide); (b) bromide (lithium bromide, sodium bromide, potassium bromide); (c) chloride (lithium chloride, sodium chloride, potassium chloride, cesium chloride)

Fig. 14. The relation between the refractive index of salt solution and the refractive index and concentration of solute^[47]. (a) The change of detection signal intensity with the refractive index of the solution, where the red dashed line indicates the quadratic fitting curve; (b)‒(d) the detection signal intensity changing with the concentration of iodized salt, bromide salt, chloride salt solution

Fig. 15. Incoherent detection using different salt solutions^[47]. (a)‒(c) TISH signals for aqueous iodide solutions (cesium iodide, lithium iodide, sodium iodide, potassium iodide), salt bromide (lithium bromide, sodium bromide, potassium bromide) solutions and salt chloride (lithium chloride, sodium chloride, potassium chloride, cesium chloride) solutions, and pure water detection; (d) relationship curve of TISH energy and linear refractive index of different solutions; (e) concentration dependence of the measured peak TISH energy signal intensity on the six representative solutions

Fig. 16. Diagram of a system setup for coherent detection of terahertz waves with ethanol^[51]

Fig. 17. The terahertz waveforms and corresponding spectra detected by ethanol, pure water, and air^[51]. (a) Terahertz waveform; (b) corresponding spectrum

Fig. 18. Terahertz time domain waveforms measured based on ethanol (solid) and water (dashed) at different terahertz electric field intensities and at a detection light energy of 5‒30 μJ^[51]. (a) At different terahertz electric field intensities; (b) at a detection light energy of 5‒30 μJ

Fig. 19. Experimental setup and TKE response^[12]. (a) Schematic diagram of the experimental setup; (b) TKE response of water excited by terahertz pulses with different electric field intensities

Fig. 20. Simulation and fitting results^[12]. (a) The simulated electron response and molecular directional motion in liquid water and the molecular response triggered by the stretching and bending vibration of hydrogen bonds between molecules; (b) measured TKE response results (blue line) and theoretical fit results (red line)

Fig. 21. Comparison of TKE responses in liquid and heavy water^[52]

Fig. 22. TKE response of terahertz pulses to heavy water under different low-pass filters^[52]. (a) 18 THz; (b) 9 THz; (c) 6 THz; (d) liquid water, illustrated by the results of theoretical fitting

Fig. 23. Related curves of ethanol at different terahertz electric field intensities^[12]. (a) TKE reactions of ethanol at different terahertz electric field intensities; (b) TKE responses and simulated electronic and molecular responses of ethanol on sub picosecond and picosecond time scales

Fig. 24. TKE responses of ethanol-water mixtures at different molar concentrations, and the illustration shows the normalized TKE responses of mixtures at C=100%, 70%, 40% and at t=5 ps^[52]