模式锁定是一种产生皮秒([latex]10^{-12}[/latex] 秒)到飞秒([latex]10^{-15}[/latex] 秒)级极短激光脉冲的技术。它的工作原理是迫使激光腔的多个纵向模式以固定的相位关系振荡。这将导致这些模式发生建设性干涉,从而产生一个在腔内循环的单个高强度超短脉冲。.

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模式锁定是一种产生皮秒([latex]10^{-12}[/latex] 秒)到飞秒([latex]10^{-15}[/latex] 秒)级极短激光脉冲的技术。它的工作原理是迫使激光腔的多个纵向模式以固定的相位关系振荡。这将导致这些模式发生建设性干涉,从而产生一个在腔内循环的单个高强度超短脉冲。.
典型的激光腔支持多个纵模,每个纵模对应一个特定的谐振频率。在正常的自由运转激光器中,这些模式以随机相位独立振荡。锁模技术可以使这些模式的相位同步。当模式相位锁定时,它们在特定的时空点发生相长干涉,形成一个强度高、持续时间短的脉冲。在其他所有时刻,它们发生相消干涉,导致脉冲强度接近于零。最终,激光腔内会循环出现一串超短脉冲,每次往返都会从输出耦合器发射一个脉冲。
The duration of a mode-locked pulse is inversely proportional to the spectral bandwidth of the gain medium. A wider gain bandwidth supports more longitudinal modes, which can be locked to create a shorter pulse. This is governed by the Fourier uncertainty principle: [latex]\Delta t \Delta u \ge K[/latex], where [latex]\Delta t[/latex] is the pulse duration, [latex]\Delta u[/latex] is the spectral bandwidth, and K is a constant near unity. Techniques for achieving mode-locking can be active (using an external modulator like an acousto-optic modulator) or passive (using a saturable absorber, a material whose absorption decreases at high light intensity). Passive mode-locking, particularly Kerr-lens mode-locking, has produced the shortest pulses to date, reaching the attosecond ([latex]10^{-18}[/latex] s) regime.
锁模(激光器)
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