Control laser-induced association

It is well known that high-quality three-dimensional photonic stmctures, e.g., buried chaimel waveguides, which can be used for laser emissions, have been readily created on transparent laser ceramics, by using irradiations of short-pulse lasers [263-271] and particle beams [272—278]. This process is based on the controlled modification of the refractive index of the electronic processes and thermally induced transformations associated with laser irradiation. Laser writing to create such structures is a one-step process without the requirement of special preparation. It is a very fast, highly reproductive, and thus low-cost process. It has been employed to fabricate various integrated photonic devices. 

Phase-dependent coherence and interference can be induced in a multi-level atomic system coupled by multiple laser fields. Two simple examples are presented here, a three-level A-type system coupled by four laser fields and a four-level double A-type system coupled also by four laser fields. The four laser fields induce the coherent nonlinear optical processes and open multiple transitions channels. The quantum interference among the multiple channels depends on the relative phase difference of the laser fields. Simple experiments show that constructive or destructive interference associated with multiple two-photon Raman channels in the two coherently coupled systems can be controlled by the relative phase of the laser fields. Rich spectral features exhibiting multiple transparency windows and absorption peaks are observed. The multicolor EIT-type system may be useful for a variety of application in coherent nonlinear optics and quantum optics such as manipulation of group velocities of multicolor, multiple light pulses, for optical switching at ultra-low light intensities, for precision spectroscopic measurements, and for phase control of the quantum state manipulation and quantum memory. 

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