Plasma, recognized as the fourth state of matter, exhibits unique properties that make it well suited to laboratory studies and technological applications. In this work, key plasma parameters—including expansion velocity, temperature, and density—were experimentally measured using the shadowgraphy technique. Experiments were carried out with an Nd:YAG laser at pulse energies of 140 and 200 mJ in two different environments: air and water. Plasma was generated using the fundamental wavelength of 1064 nm, while the second harmonic at 532 nm was employed for shadowgraphy imaging. Time-resolved images recorded at delays of 1–10 μs enabled detailed analysis of the propagation of the plasma front. The results show that the average plasma expansion velocity is 3.54 km/s in air and 2.74 km/s in water, while the plasma temperature is 3435 K in air and 2008 K in water. The estimated plasma densities in air for pulse energies of 140 and 200 mJ are 5.04 and 5.35 kg/m³, respectively, and 4.91 and 4.95 kg/m³ in water. Analysis of the temporal evolution of these parameters reveals a gradual decrease in temperature, velocity, and density after plasma formation. These findings confirm that shadowgraphy is an effective tool for accurate diagnostics of laser-induced plasma and for comparative studies in different media. Furthermore, the high sensitivity and dynamic behavior of such plasmas provide promising opportunities for applications in optical cryptography and sensitive environmental monitoring, where spatial and temporal plasma patterns can serve as data-encoding channels or environmental indicators, with small changes in the surrounding medium directly affecting plasma parameters. This research can contribute to the design of next-generation laser systems and advanced technological applications for information transfer and environmental surveillance.