Control of coherent optical phonons
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Using time-resolved reflectometry we measure the dielectric function of tellurium following excitation with a femtosecond laser pulse. The dielectric function reveals the ultrafast dynamics of coherent phonons in Te. Oscillations in the bonding-antibonding splitting allow for THz modulation of a semiconductor-semimetal transition. Using two-pulse sequences, we can control the phonons, stabilizing the bandstructure in the semimetallic state.