Nonlinear optics is the study of how light interacts with matter in ways that depend nonlinearly on the intensity of the light. In these scenarios, the response of the material (such as polarization) is not directly proportional to the electric field of the light.
Key Concepts:
- Occurs at high light intensities, such as those from lasers.
- Leads to phenomena that cannot happen in linear optics.
Common Nonlinear Effects:
- Second-harmonic generation (SHG): doubling the frequency (halving the wavelength) of light.
- Third-harmonic generation (THG): producing light at three times the original frequency.
- Self-focusing: intense beams can focus themselves in nonlinear media.
- Kerr effect: intensity-dependent refractive index.
- Four-wave mixing and optical parametric amplification: allow generation and control of new frequencies.
Applications:
- Laser technology, telecommunications, quantum optics, medical imaging (e.g., nonlinear microscopy), and frequency conversion for spectroscopy.
Nonlinear optics is crucial for advancing technologies that rely on manipulating light with light.