Mode Locking of Lasers

Generation of Ultra-high Speed Pulse and Single-Frequency Light

Abstract

The behavior of mode locking has been introduced in detail with respect to gaseous and solid lasers. There are two types of mode-locked lasers, which are classified as AM (Amplitude modulation) type and FM (frequency modulation) type. The former, which is realized by virtue of the internal loss modulation or the nonlinearity of laser medium, emits a train of ultra-high speed light pulse, whereas the latter, which is realized by the internal phase modulation only, emits a frequency-modulated light wave. The mode-locked laser of AM type with m light pulses bouncing back and forth between both the end mirrors oscillates ordinarily at mƒ_p mode interval (ƒ_p is the fundamental axial mode interval) and exceptionally at 1ƒ_p mode interval. The condition of these lockings is discussed concerning mirror separation as well as oscillation intensity and proved to concern closely the decay constants, etc., of laser medium. Some special considerations on the realization of mode locking are also given. Such mode-locked lasers will be applied to ultrahigh speed PCM communication, ultra-high speed photograph, generation of single-frequency light, and so on.