Dynamic behavior of gas lasers
Dynamic behavior of gas lasers
复制标题
气体激光器的动态行为
DOI：
10.1109/jqe.1967.1074363
复制
发表时间：
1967
影响因子：
2.5
通讯作者：
T. Uchida
中科院分区：
文献类型：
--
作者：
T. Uchida
本文的目的是系统地处理气体激光器在内部调制、锁模、组合音引起的模式扰动以及自发发射引起的噪声方面的特性。基于兰姆光学微波激射理论，研究了气体激光器对谐振腔损耗调制和小外部信号注入的响应。对低频损耗调制的分析表明，气体激光器中的每种振荡模式对于两种扰动都有其适当的阻尼常数或截止频率。虽然该阻尼常数在阈值附近由激光作用引起的负电导率的一次项与谐振器损耗电导率之差的两倍确定，但随着振荡强度的增加，它收敛于由谐振器损耗电导率确定的阻尼常数。对小外部信号注入的分析给出了锁模的判据，并阐明了由此引起的振荡模式的复杂扰动。在强制锁定的情况下，其中谐振器损耗以几乎等于轴向模式间隔的频率进行调制，每个模式的落在其相邻模式附近的边带分量相当于外部注入信号。因此，用于强制锁定的KDP腔内调制器两端所需的调制电压可以根据用于小外部信号注入的前述锁定标准来估计。还解释了由于激光介质的非线性而产生的组合音调，相当于外部注入信号，在振荡模式周围产生复杂的频谱，从而产生未锁频气体激光器的主噪声，并在一定条件下引起自锁定。此外，自发发射的扰动也对应于小的外部信号注入。因此，使用小外部信号注入的分析结果可以轻松计算出自发辐射引起的噪声。将激光介质的宏观偏振发展为幂级数的表示法被证明不适用于具有中等输出功率的实用氦氖气体激光器，并且分析扩展到更一般的情况，其中偏振由单调饱和函数表示。
The purpose of this paper is to treat systematically the properties of gas lasers with respect to internal modulation, mode locking, perturbation of modes due to combination tones, and noise due to spontaneous emission. The response of gas lasers to the resonator loss modulation and the small external signal injection has been investigated on the basis of Lamb's optical maser theory. The analysis on the low-frequency loss modulation indicates that each oscillating mode in a gas laser has its proper damping constant or cutoff frequency for both the perturbations. Although this damping constant is determined in the vicinity of threshold by twice the difference between the first-order term of the negative conductivity due to laser action and the resonator loss conductivity, it converges to that determined by the resonator loss conductivity with the increase of oscillation intensity. The analysis on the small external signal injection gives the criteria of mode locking and clarifies the complex perturbation of oscillating modes due to it. In the case of forced locking where the resonator loss is modulated at a frequency nearly equal to the axial mode interval, the sideband components of each mode falling near its neighboring modes are equivalent to externally injected signals. Accordingly, the required modulation voltage across the KDP intracavity modulator for forced locking can be estimated from the foregoing locking criteria for the small external signal injection. It is also explained that the combination tones due to the nonlinearity of the laser medium, which are equivalent to externally injected signals, produce the complex frequency spectra around the oscillating modes, which result in a principal noise of unlocked gas lasers, and give rise to self locking in a certain condition. Besides, the perturbation by spontaneous emission also corresponds to the small external signal injection. The noise due to spontaneous emission is, therefore, easily calculated using the analytical results on the small external signal injection. The representation of the macroscopic polarization of laser medium developed into power series is shown to be inappropriate to a practical He-Ne gas laser with medium output power, and the analysis is extended to the more general case, where the polarization is represented by a monotonically saturating function.