FIG. 3.

Transformations of plasma Langmuir oscillations into upper-hybrid resonance waves. (a) Plasma oscillations at F = 25 mJ/cm² under different magnetic fields. (b) Expansion of plasma cloud at F = 25 mJ/cm² without magnetic field. (c) The transition of plasma oscillations into upper-hybrid waves at two laser fluences. The inset summarizes the $T_e$ deduced from different laser intensities (P) based on Ref. 32 (solid symbols) and the studies here (open symbols). The experimental data are fitted (in red solid line) with $\Delta \sigma \left(t\right)=A_c\hspace{0.17em}\text{sin}\hspace{0.17em}\left(2\pi f_c+{\varphi }_c\right)e^{-\frac{t}{\tau }}+A_{uh}\hspace{0.17em}\text{sin}\hspace{0.17em}\left(2\pi f_{uh}+{\varphi }_{uh}\right)\left(1-e^{-\frac{t}{\tau }}\right)$, where $A_i$ and ${\varphi }_i$ represent the amplitude and phase of the two plasma waves, respectively. The dashed blue line and solid green line outline the decay and the rise of the waves at $f_c$ and $f_{uh}$ with the same time constant τ, respectively.