Strong optical feedback in birefringent dual frequency laser

Strong optical feedback in a birefringent dual frequency He--Ne laser with a high reflectivity feedback mirror has been investigated for the first time. The output characteristics of two orthogonally polarized modes are demonstrated in two different optical feedback cases: one is for both modes being fed back and the other is for only one of the modes being fed back. Strong mode competition can be observed between the two modes with strong optical feedback. And when one mode's intensity is near its maximum, the other mode is nearly extinguished. When both modes are fed back into the laser cavity, the mode competition is stronger than when only one mode is fed back. The difference in initial intensity between the two orthogonally polarized modes plays an important role in the mode competition, which has been experimentally and theoretically demonstrated.     

Intensity modulation in single-mode microchip Nd：YAG lasers with asymmetric external cavity

Intensity modulation induced by the asymmetric external cavity in single-mode microchip Nd:YAG lasers is presented. Two kinds of experimental results are discussed based on multiple feedback effects. In one case, the intensity modulation curve is a normal sine wave, whose fringe frequency is four times higher than that of a conventional optical feedback system, caused by multiple feedback effects. In the other case, the intensity modulation curve is the overlapping of the above quadruple-frequency signal and conventional optical feedback signal, which is determined by the additional phase difference induced by the asymmetric external cavity. The theoretical analyses are in good agreement with the experimental results. The quadruple-frequency modulation of the laser output intensity can greatly increase the resolution of displacement measurement of an optical feedback system.     

Optical feedback characteristics in a helium neon laser with a birefringent internal cavity

The output characteristics of optical feedback in a helium neon laser with a birefringent internal cavity are studied systematically in five different regions of the gain curve for the two orthogonally polarized modes. When the laser operates in the two end regions of the laser gain curve, one of the two orthogonally polarized modes will be a leading one in optical feedback. Strong mode competition can be observed. However, when the laser operates in the middle region of the laser gain curve, the two modes can oscillate equally with optical feedback. Besides the intensity of the two polarized lights, the total light intensity is also studied at the same time. M-shaped optical feedback curves are found. Particularly, when the average intensities of the two lights are comparable, the intensity modulation curve of the total light is doubled, which can be used to improve the resolution of an optical feedback system.[第一段]     

Self-mixing interferometry based on nanometer fringes and polarization flipping

Self-mixing interferometry (SMI) based on nanometer fringes and polarization flipping is realized. The interferometer comprises a single-mode He-Ne laser and a high-amplitude reflectivity feedback mirror. The nanometer fringes are obtained by tilting the external feedback mirror. The fringe density is 35 times higher than that derived with conventional two-beam interference, and each fringe corresponds to a λ/70 displacement in external cavity length. Moreover, polarization flipping occurs when the external feedback mirror moves in the opposite direction. Such movement can be used to easily distinguish displacement direction. Experimental results show an optical resolution of displacement measurement of 9.04 nm with a range of 100 μm. The proposed SMI presents promising application prospects in precisely measuring displacement and calibrating other micro-displacement sensors because of its optical wavelength traceability.     

基于激光回馈的波片在盘位相延迟测量系统

 利用激光回馈测量波片相位延迟精度高的优越性,以激光回馈技术为基础,实现光学波片的在盘测量,即在加工过程中,波片光胶于光胶盘的状态下测量波片位相延迟,以提高波片生产效率和成品率。采用凹面镜作为回馈镜以提高回馈信号调制深度,对激光回馈内、外腔长进行稳定,提高了系统可靠性;研究了波片与光胶盘光胶对波片测量的影响,提出并验证了在光胶盘上开孔,在打孔的光胶盘上光胶、加工、测量波片的新工艺,最终实现了波片在盘测量,测量长期重复性优于1°,经过激光频率分裂系统校正后,系统精度优于0.5°。     

两种甲氧基苯基咔咯铜配合物的合成及光谱性质

合成了两个中位苯基上具有甲氧基取代基的铜咔咯配合物(Tp-OCH3PC)Cu和(To,p-(OCH3)2PC)Cu,通过紫外-可见、红外光谱、元素分析、核磁共振及质谱对它们进行了表征。研究了配合物在非水溶剂中的电子顺磁共振、电化学和光谱电化学性质,结果表明无论在固体状态还是在非水溶剂中,配合物的中心金属离子均为三价铜Cu(Ⅲ),在给定的溶剂中Cu(Ⅲ)可以发生可逆的还原反应生成Cu(Ⅱ),也可以被可逆氧化为Cu(Ⅲ)的阳离子自由基。探讨了甲氧基取代基以及溶剂对配合物的紫外-可见光谱和氧化还原电位的影响。     

Hilbert空间的正交序列与Kubert恒等式

主要讨论了与Kubert恒等式有关的一些积分性质以及Hilbert空间中的正交序列与Kubert恒等式之间的关系,并给出利用这些关系来构造Hilbert空间中几个具体的正交序列.     

各向异性外腔微片Nd:YAG激光器调频回馈研究

研究了在各向异性外腔下微片Nd:YAG激光器调频回馈特性.作为对比,首先给出了在各向同性外腔下调频回馈结果,激光器输出功率的半波条纹数正比于外、内腔长度之比.在回馈外腔中内置一个四分之一波片,激光偏振态发生规律性跳变,每个纵模带宽内的偏振跳变次数正比于外、内腔长之比,相同外腔长下,回馈条纹再次倍频.进行了基于法布里-珀罗腔等效模型的理论分析,结果和实验相符合.此现象在精密测量领域有潜在应用. 关键词： 光回馈 调频回馈 各向异性外腔 半波条纹数     

腔调谐过程中激光器中两垂直偏振光的回馈特性

腔调谐过程中同时对HeNe激光器进行光回馈，设定回馈镜驱动信号的周期远小于腔调谐信号的周期，此时便获得腔调谐过程中谐振腔中两垂直偏振光的回馈信号. 回馈的形式分为仅垂直光回馈、仅平行光回馈以及两光同时回馈三种情况. 当两光同时回馈时，两模式间的模竞争较弱，两光回馈曲线有一定的相位差，该相位差小于180°，两光总体波动幅度变化趋势相反. 当仅单偏振光回馈时，两模式间的模竞争较强，两光回馈曲线始终反相，而且两光波动幅度变化趋势相同，此时可以将两光强度信号相减以实现成倍提高回馈信号幅度，从而提高系统灵敏度. 尤其仅垂直光回馈时，两光各自光强波动幅值都较大，并且在较大的增益曲线范围内保持光强波动幅值无明显变化，该特性可用于提高回馈系统的抗干扰能力，减少因激光功率漂移而引起的错误计数. 关键词： 自混合干涉 光回馈 模竞争 位移测量     

Intensity Tuning Characters of Frequency Split Lasers

Laser frequency splitting generated by intracavity birefringence elements has been applied widely, but tuning characters of such lasers have not been successfully studied quantitatively. Based on the vectorial extension of Lamb‘s semi-classical theory, we study the intensity tuning of frequency splitting of He-Ne lasers. It is found that the intensity tuning curve is affected obviously by the compositive ratio of isotopes in the gain medium and the frequency difference of splitting modes. The threshold of locking is also quantitatively obtained. All the calculations are consistent with the experimental results.