A liquid-crystal based phase-shaper for multi-octave light sources

The growing development of few-cycle light sources has triggered the development of innovative pulse shaping devices, capable of handling bandwidths spanning over multiple optical octaves [1] . We propose an ultra-broadband reflective SLM, whose design is issued from our previous investigations on thick cells of thermotropic nematic liquid crystal (LC) [2] , [3] . It overcomes the typical limitations of LC-SLM, by eliminating the need for an electrode. The device, referred to as a Thermo-Optically-Addressed Spatial Light Modulator (TOA-SLM), relies on an optically-induced change of the local temperature of a liquid crystal layer ( Figure 1a ). The temperature is controlled by "recording" beam, while the "readout" beam is the modulated beam. The optical isolation between the recording and readout beams is performed by a gold layer which endorses three additional functions: partial absorption of the recording beam, local heating of the LC by diffusion, and reflection of the readout beam. TOA-SLM also includes two substrates and a layer of 50-100 μ m of the nematic mixture E7. The LC being thermotropic and birefringent, both the ordinary and extraordinary optical refractive indices are locally modulated. Arbitrary phase modulation is then achieved by spatially shaping the recording laser.