Femtosecond pulse shaping by dynamic holographyin photorefractive multiple quantum wells

Abstract

In applications in optical communication and information processing, the ability arbitrarily to manipulate ultrafast pulses is of great interest and practical importance. The use of femtosecond lasers offers possibilities of exploiting the large bandwidth of optics. Shaping laser pulses on the femtosecond (fs) time scale was demonstrated in 1988. Since then, extensive research has been done in this area, – 8 much of it based on Fourier synthesis techniques in which the optical frequency components of a fs pulse are manipulated by an amplitude or phase mask in the Fourier domain. By changing the mask, one can obtain different-shaped pulses. Such an apparatus is usually called a pulse shaper. Either permanent transmission or holographic masks made by microlithography techniques or programmable spatial light modulators can be put into the pulse shaper. – 7 Picosecond pulse shaping experiments using bulk photorefractive materials have demonstrated the possibility of real-time control over the hologram, limited only by the material response time. Photorefractive multiple quantum wells (MQW’s) have high nonlinear sensitivities sDn , 1022d with small driving intensities s,10 mWycm2d and fast response times s,msd. – 11 The holograms in MQW’s are thin, and the diffraction is in the Raman–Nath regime. No Bragg matching is necessary, which makes the alignment of the system simpler. MQW’s can also be designed by band-gap engineering to match different application wavelengths, such as 1.55 mm for optical fiber communications. In the femtosecond regime, photorefractive MQW’s were previously used for electric-f ield cross-correlation measurements and for time-to-space conversion experiments. We report here, for the first time to our knowledge, the experimental demonstration of femtosecond pulse shaping with photorefractive MQW’s in a pulse shaper. Figure 1 shows the top view of the experimental setup, which eliminates temporal dispersion and permits a possible synthesis of fs pulses. The setup is similar to that of the standard pulse shaper, with two differences related to the use of dynamic holography. First, a photorefractive MQW instead of a mask