Fig. 3: Two-pulse pumping and accumulated echo.
Pumping consists of two consecutive pulses of frequency ω0 and duration 1 μs, separated by a delay τ, and repeated N times after a waiting time 200 ms. a Measured reflection coefficient without (orange line) and with (blue line) two-pulse pumping. b Computed spectral power density of the two pulses; it goes to zero at frequencies \({\tilde{\omega }}_{k}\) (see text). c Measured Er3+ density ρ1(ω) after two-pulse pumping, renormalized to the reference density ρ0(ω). It shows a periodic pattern of anti-holes at frequencies \({\tilde{\omega }}_{k}\). d, e The blue line is the measured average value of the I quadrature following a microwave pulse (purple part) at ωp, after a periodic grating was generated by two-pulse pumping with τ = 50 μs (d) and τ = 100 μs (e). f First-echo amplitude Ae as a function of N. green (pink) dots are measurements (simulations). g The blue line is the measured average value of the I quadrature following three consecutive microwave pulses (purple) at ω0, after a periodic grating was generated by two-pulse pumping with τ = 200 μs. The inset is a zoom on the three generated echoes.
