  Efficient production of high-charge electron bunches in laser wakefield
acceleration using a mid-infrared (MIR) laser pulse is investigated by
two-dimensional particle-in-cell simulations. Only a 2.5 TW (100 mJ, 40 fs) MIR
laser pulse with a wavelength of 1.5 um can produce a quasi-monoenergetic
electron (QME) bunch with a peak energy of 65 MeV in the blow-out regime. The
simulation results are compared with those for the experiment showing the
generation of 40-60 MeV QME bunches with more than 10^8 electrons using an 8 TW
laser pulse with a wavelength of 0.8 um. The number of electrons in the QME
bunch produced by a 1.5 um laser is 10 times higher than that produced by a 0.8
um laser, and is equivalent to 10^9. The conversion efficiency from the laser
energy to the QEM bunch energy is more than 10%. Laser wakefield acceleration
by a TW-class MIR laser pulse opens the door to generating a high-charge QME
bunch with high efficiency.
