Lez #27+28 Introduction to 3rd order spontaneous vs stimulated processes, classical approach

 We introduced the field-induced polarization, in both the spontaneous and stimulated cases. We discussed the origin of spontaneous Raman, and why it is incoherent, linear and homodyne. As for the selection rules we recalled some basic notions from struttura della materia class. Then we moved to the stimulated Raman, a third order process for which we evaluated different contributions to the polarization. See the material on classroom.

Lez #25+26 Principles of laser II and Wavemixing I

 We first finalized the laser lecture introducing the solid state laser principle. Then mode locking for pulsed laser generation, active and passive methods, gain and losses compensation.  

Starting from Maxwell equation in presence of a dielectric, non magnetic  we re-derived the differential equation for the pulse envelope in presence of linear polarization in a slightly different way.

We then extended to a non linear term, considering the specific case of second order. The most general case is here a three waves mixing, approximating one beam (the pump) much more intense then the others, the signal (initially weak) and the idler (initially empty).

Lez #23+24 First ESONERO

Lez #21+22 Experimental techniques for pulsed laser characterization. Autocorrelator.

  We discussed different type of autocorrelation techniques for measuring the duration of ultrashort pulses, namely linear autocorrelator, non-collinear SHG autocorrelator and collinear SHG autocorrelator, discussing the different advantages/disadvantages. We also introduced FROG (frequency-resolved optical gating) as a convenient approach to characterize an optical pulse.

Lez #19+20 Simulazione di Esonero

We solved an old, slightly modified test. 

Lez #17+18 Principles of Laser I

 Recap on Absorption, Spontaneous and stimulated emission. Laser principles, treshold condition. Passive resonator. Is a laser superior to a conventional sources? Trading spatial and temporal coherence with flux. Statistical properties of light. How to make a laser: 2/3/4 level systems. Different type of lasers, He-Ne, ruby, excimers.