High Bandwidth Scanner Based on Spatial-Spectral Holograms

摘要

I experimentally demonstrated a high bandwidth spatial-spectral holographic (SSH) scanner. Scanners or true time delay lines find their applications in phased-array antennas, radar range- Doppler processing and time-frequency ambiguity function analysis. A typical example of such a device is an acousto-optic deflector (AOD), which has limited bandwidth due to Bragg match conditions, frequency dependent acoustic attenuation of available materials and limitations of piezoelectric transducer technologies.The system proposed in this thesis breaks through the bandwidth limitation of acousto-optic technology, yet resembles the function of an AOD since both operates as a scrolling scanner. It uses a material with large inhomogeneous bandwidth to record space-dependent time-delays as spatial spectral holograms. The recording of the spatial-spectral holograms utilizes a Galvo scanning (GS) mirror and a chirped laser.In Chapter 2, I experimentally show that a GS mirror can be sufficiently stable for the holographic recording process. After reviewing the relevant physics of the spatial-temporal holographic recording medium, the cryogenically-cooled rare earth doped crystals, in Chapter 3, I give further derivations that are useful in explaining the subsequent experimental results. Chapter 4 describes an efficient and stable numerical scheme for simulating the coherent light-atom interaction in a two dimensional inhomogeneously-broadened crystal, allowing a search for the optimum experimental geometry for the recording experiment. Chapter 5 integrates the Galvo scanning mirror with the Tm3+:YAG crystal, and gives the experimental demonstration of the ¯first high bandwidth (1:5GHz bandwidth with 20 resolvable spots) spatial-spectral holographic scanner. This system uses one laser for the proof-of concept experiment. Finally, in Chapter 6, I explore the prospect for the future development of the high bandwidth SSH scanner. This chapter also gives the design and demonstration of a two-laser stabilization circuit, with which we can extend our ability to realize the full version of the high bandwidth SSH scanner system.