First published by New Age International, B.B. Laud’s text occupies a unique middle ground. It is less encyclopedic than Saleh & Teich’s "Fundamentals of Photonics" and less relentlessly mathematical than Robert W. Boyd’s "Nonlinear Optics." Instead, Laud offers clarity.
Deep within the shelves of the Great Library lay a tome bound in blue and white, its spine reading simply: Laser and Nonlinear Optics by B.B. Laud. To the average student, it was a collection of formulas and diagrams. But to those who looked closely, it was the epic history of the Photon War.
As Lux stepped into the Caverns, something miraculous happened. He looked at his reflection, but it wasn't quite right. laser and nonlinear optics by bblaud pdf top
The crystal was vibrating, mixing the frequencies of his laser beam. Suddenly, a new light appeared—a ghostly, ethereal blue beam walking beside him.
"Who are you?" Lux asked the blue light. First published by New Age International, B
"I am you," the blue light replied, "but faster. I am the Second Harmonic."
In the high-intensity heat of the battle, the nonlinear susceptibility of the crystal ($\chi^(2)$) had acted as a mixer. It had taken two red photons and merged them into one blue photon with double the frequency. It was Frequency Doubling. Boyd’s "Nonlinear Optics
Lux realized the power of Laud’s teachings. By breaking the linearity of the world, he could change the very color of reality. He could turn invisible infrared into visible green. He could perform Parametric Amplification, splitting one photon into a 'signal' and an 'idler' to explore new wavelengths never before seen by man.