Fig. 1. Schematic of laser chirp controlled few-cycle mid-IR pulse generation. Due to the special curving profile of the refractive index of the NCLP and the plasma etching, the pulse is rapidly compressed longitudinally. As a result, a large number of photons approach the photon deceleration phase, and produce the mid-infrared frequency component, which then slips backwards into the bubble and moves forward together with the bubble. The red curves represent the distribution of the laser electric field on-axis, and the green curves represent the corresponding distribution of the refractive index of the NCLP. The blue arrows denote the photon emission directions relative to the bubble.

Fig. 2. 2D simulation of mid-IR generation with the NCLP. (a)–(c) Distributions of the plasma density () and transverse electric field () at different times. The orange curve is the electron density on-axis. (d) Spectral evolution as a function of the propagation time. (e) Spectral distribution of the on-axis laser electric field at (blue), (black) and (red). (f) Temporal profile of the mid-IR electric field at .

Fig. 3. Comparison of refractive index and evolution of the NCLP and un-chirped pulse. Longitudinal distribution of the laser electric field and refractive index in the cases of (a) and (b) an un-chirped laser. (c), (d) The corresponding locations of the rise edge and the fall edge, corresponding to the case with and without chirp, respectively. The insets of (c) and (d) show the evolution of the laser peak electric field .

Fig. 4. The evolution of the CEP at . (a) The generated mid-IR electric field as a function of the initial drive pulse phase . The inset shows the electric field waveform for different of the initial drive pulse (, blue dashed; , black solid; , red dot dash). (b) The phase evolution of the mid-IR electric field with variation.

Fig. 5. 3D simulation of mid-IR generation with the NCLP. (a)–(c) The distributions of the plasma density () and the transverse electric field () at different times obtained from 3D PIC simulation. (d) Spectral distribution of the on-axis laser electric field at (blue) and (red). The inset is the temporal profile of the mid-IR electric field at .