Design Of Grating Feedback External Cavity Tunable Diode Laser System

The aim of my thesis is to design a grating feedback external cavitytunable diode laser (ECTDL) system, and use it in lab works. To accomplishthis purpose, we begin with the basic knowledge fundamental rules about laser.I also noticed the characters of the diode laser, such as their performancewhen changing surrounding temperature or changing working current. I alsostudy many papers focus on this aspect. I make this design taking manyrelated problems into account. Such as, the choice of the external cavitylength, the choice of the formation of beam path, the allowance error of thebeam path, mechanical stability, passive temperature stability, and so on. Thetest of our laser system shows that it is well done. Firstly, we begin with the basic rules and fundamental concepts of laser.They are the foundation of all our theory. We can summarize them into twosentences: light is spreading in the active media; the function of the opticalresonator. The first thing amplifies the light, and the second maintains the76 吉 林 大 学 硕 士 论 文英 文 摘 要vibrations of the light. As we know, LASER is the initials of LightAmplification by Stimulated Emission of Radiation., which indicates thatinteract between the amplification and the vibration make the laser possible.The basic rules of laser including: 1. The energy of the laser is highly concentrated in a very little space. 2. The laser is spatially coherent light. 3. The laser is time-coherent light. Diode laser is a newly developing type in laser family, but it is widelyused in many fields now. The emitting theory of diode laser is therecombination of electrons in the conduction band with positive hole in thevalence band. Its merits include little package, long lifetime, low cost, nonoise, and easily controlled by changing work current. Its shortcomings arealso obvious, including sensitive to back light, wide line-width, changingoutput with temperature flow, multi-modes, no well collimation, and so on.ECTDL is to correct the demerits of diode laser using the external cavity. Many devices had been used as the tunable filters, such as diffractiongrating, distributed bragg reflector, fabry-perot etalon, interference filter,acoustic-optic tunable filter. Diffraction grating is the most easy way to makea ECTDL. There are two configurations of grating feed back ECTDL, Littrowand littman. Each of them has merits and demerits, Littrow configuration iseasy to build, and has bigger power output comparing with littman. So wedecide to build a littrow mounting ECTDL. 吉 林 大 学 硕 士 论 文 77英 文 摘 要 Here we generalize the functions of external cavity as following: 1. To choose the needed mode by the grating filter. 2. To get a narrowed linewidth by extending the cavity length from nl to L+nl. 3. To change the frequency of the laser by shift the angle of the grating step by step. Based on the knowledge of first chapter, I do the design work in Chaptertwo. Here I convert the work into several small parts as following: 1. To choose laser diode. Diode lasers are different from each other. We need to know its characters including frequency, mode, power, package, current, temperature, and so on. We use the Sony diode laser, output 653nm, 3mw, when the working current is 70mA. 2. To choose the grating. This work is well done by following the table 2.1 and other tips in §2.2. 3. To design the light path. We choose the littrow configuration. It is showed in figure1. Figure 1. the light path in littrow configuration ECTDL78 吉 林 大 学 硕 士 论 文英 文 摘 要4. The mechanica...