Figure 1

(a) Sketch of the scheme: Two laser pulses with different frequencies, \(\omega _{1}\) and \(\omega _{2}\) collide obliquely with each other on an overdense plasma sheet of nm thickness. From the region of the colliding laser pulses, beat-frequency radiation \((\Delta \omega =\omega _{1}-\omega _{2})\) is emitted into the vacuum. Snapshots of spatial distributions of; (b,c) laser field \(E_{z} (\text {V}/\text {m})\) (s-polarized), (d) total radiation field \(B_{z} (\text {T})\) (p-polarized), (e) filtered radiation field \(B_{z} (\text {T}\)), and (f–h) plasma electron number density \(n_{e} (\text {m}^{-3})\), at different times; \(t=220\; \text {fs}\), \(320\; \text {fs}\), and \(390\; \text {fs}\).