Scaling up the energy of THz pulses created by optical rectification

The possibility for up-scaling the energy of sub-ps THz pulses generated by tilted pulse front excitation is demonstrated. Using 150-fs-long 500 muJ optical pump pulses at 800 nm up to 240 nJ THz pulse energy has been achieved. For a 1.2 mm2 pump spot area, the energy conversion efficiency of pump energy to THz pulse energy had a maximum of 5 x 10-4 at 300 muJ pump pulse energy. The corresponding photon conversion efficiency amounts to 10 %. For comparison, the maximum attainable THz pulse energy was limited to 3.1 nJ if a line focusing excitation geometry was utilized. This limit was reached at 32 muJ pump energy. For the latter configuration the THz energy dropped for larger pump energies. The tilted pulse front excitation allows further up-scaling of the THz pulse energy by using a larger pump spot size and still stronger pump pulses.