Sample interview questions: What are some common techniques for achieving mode-locked laser output in the near-infrared range?
Sample answer:
- Kerr-lens mode-locking (KLM):
This technique relies on the self-focusing effect induced by the intensity-dependent refractive index of the gain medium. As the laser beam propagates through the gain medium, its intensity variations lead to spatial variations in the refractive index, which in turn result in self-focusing or self-defocusing of the beam. This self-focusing action can be used to select a single longitudinal mode by introducing an intracavity aperture that transmits only the central portion of the beam, which has the highest intensity. - Passive mode-locking (PML):
PML involves the use of intracavity optical elements that introduce a nonlinear phase shift that is dependent on the optical intensity. Common PML techniques include:- Saturable absorbers: These devices have a transmission that decreases with increasing optical intensity. When placed inside the laser cavity, they preferentially transmit the short, intense pulses, while attenuating the longer, weaker pulses.
- Semiconductor saturable absorber mirrors (SESAMs): SESAMs are semiconductor-based devices that exhibit saturable absorption properties. They are typically used as output couplers in mode-locked lasers, providing both mode-locking and output coupling functionality.
- Active mode-locking (AML):
AML involves the use of an external modulator to introduce a periodic modulation of the laser cavit… Read full answer