Single diffractive optical element pulse shaper

Abstract

Summary form only given. Pulse-shaping technology has been acknowledged as a convenient framework for synthesizing user-defined temporal waveforms. In this context, compact, dynamic, user-friendly and fast-operation devices demanded in photonics, quantum dynamics, or ultrafast telecommunications have inspired researchers to look for simple pulse-shaper designs. In this contribution, we experimentally demonstrate pulse shaping of femtosecond pulses by using a single diffractive element encoded into a phase-only spatial light modulator (SLM) [1]. In this proposal the entire size of the pulse shaper is very small, there is almost no need for optical alignment, and obviously no extra refractive focusing element is required. This type of diffractive pulse shaper can generate bursts of flattop pulses [2] with potential application, i.e., as optical packet headers in packet-switched networks, and for the photonically assisted generation of microwave or adaptive quantum control experiments. Today, similar implementations of this device have been successfully used as a versatile, and real-time tunable optical filter [3], to generate arbitrary waveforms [4] or to synthesize sequences of fractal light pulses in the femtosecond regime [5].The output of the pulse shaper is located in the close vicinity (by few micrometers) of the focal spot of a patterned kinoform diffractive lens (DL). Its temporal amplitude is approximately given by the convolution of the initial ultrashort pulse with the transmittance of certain complex mask in r2 transformed into the time domain. To measure the temporal response of the shaper an intensity cross correlation, with a /.3 -BaB2O4 (BBO) type I non-linear crystal of 70 μm thickness, between the shaped and the reference ultrashort light pulse has been carried out. In Fig.1(a) and 1(b) experimental results for a sequences of two pulses with different peak intensity and three pulses with a slowly decreasing peak intensity are shown.In order to guarantee a constant response over the whole temporal window of the pulse shaper the amplitude of the complex mask was changed radially to compensate for efficiency losses due to the finite number of pixels of the SLM. The corresponding radial phase profiles of the complex masks used in Fig. 1(a) and 1(b) are shown in Fig1(c) and 1(d), respectively. In addition, an active correction of the wavefront aberrations at the BBO crystal plane was done, see in Fig. 1(e) an example of a distorted focus, whereas in Fig. 1(f) the corresponding correction using a commercial Shark-Harmman wavefront sensor. Please, note that the SLM is not only used to encode the complex phase mask together the DL, but also to correct for wavefront distortions.