| As a new laser species, diode pumped alkali vapor laser ( DPAL )that integratingthe merit between solid and gas flow laser has developed fast in recent years. A maintechnical difficulty of DPAL is the narrow absorption linewidth, which is only0.02~0.04nm even with buffer gases, for example helium or methane, in a pressure ofone atmosphere. But the commercial high power diode laser has a linewidth of 2~4nm.The serious mismatch of absorption and pump linewidth makes it impossible for a highefficient DPAL. To solve this problem, it is necessary to narrow the linewidth of highpower diode lasers.In this dissertation, the background and significance of this field is summarized.The linewidth narrowing methods of high power diode lasers and recent development isreviewed. Based on the plane holographic gratings, the linewidth narrowing of twokinds of high power diode lasers, single broad area diode laser and diode laser array, arenarrowed. The main work is summarized as follows:Based on the principle of line-narrowing using external cavity, the theoreticallinewidth of three external cavity configurations are calculated. The particularity of linenarrowingfor high power diode lasers is analyzed. Two formulas are deduced, one isdescribing the influence of divergence angles in both fast and slow axes on the effect ofline-narrowing, the other is describing the influence of'smile'in diode laser array. Amistake is found in literature and corrected.A single broad area diode laser with maximum output of 20W is studied. TheLittrow external cavity model is set. The results show that to get narrow linewith,grating with dense grooves, micro-lens with short focus and optical system with goodcollimating should be used, though the influence of external cavity length is small andcan be neglected. External-cavity parameters are optimized by the model, Using Littmanconfiguration, an output of 11.5W with linewidth of 0.3nm is obtained. Using Littrowconfiguration, an output of 14.35W with linewidth of 0.2nm is obtained. Additionally,experiments with different grating line density, collimating mirror focus and externalcavity configuration were done, the results show correspondence with theoreticalcalculation.A diode laser array with 64 emitters and a maximum output of 80W is studied. theinfluence of external-cavity length, fast and slow axes divergence angles and smile effecton line-narrowing effect are analyzed. The result shows that the divergence and smileare the main reason . Littman configuration is not suited for diode laser array becausesmile would be amplified in this configuration. an image inverted spherical mirrortelescope is used in a Littrow configuration. The result demonstrates an output power of31W with linewidth less than 0.2nm when output power 37W free running. By using the Talbot cavity, the homogeneity of each emitter's spectrum is enhanced, and the Rb cellrelative absorption increases to 43%.A comparison of line-narrowing for single broad area diode and diode laser array ismade. The result shows that the Littman configuration, the shorter of the micro-lensfocus are suitable for single broad area diode. While diode laser array, Littrowconfiguration and longer micro-lens focus are suitable.The conclusions of this dissertation are summarized: Based on holographic gratinghigh power diode laser external cavity.To get narrow linewidth ,the diode laser withfewer emitters, narrower free-running linewidth, and smaller smile is preferred. Thegratings should be chosen for dense grooves. The optics system should be designed tohave good collimating effect in both fast and slow axes. The micro-lens should bechosen according to the kinds of diode lasers. At last, the center of grating dispersion itshould be matched with the gain center of diode lasers. |
PDF Full Text Request