Research On All-solid-state Yellow Laser Technology For Biomedical Instruments

The 561 nm laser is the excitation light of fluorescent dyes and can be used as an ideal light source for microscopic imaging or biomedical instruments such as flow cytometry,confocal microscopy,STED microscopy,etc.At present,the laser in this band is mainly obtained by intra-cavity frequency doubling of the 1123 nm infrared fundamental wavelength.Because the three spectral lines of 1112 nm,1116nm and 1123 nm in the fluorescence spectrum of Nd:YAG crystal are too close to each other,there would be simultaneous transitions and mode competition among them.In the process of frequency doubling,the output power and stability of the 561 nm frequency-doubling light are significantly affected.Aiming at solving this problem,this paper has verified two methods to realize 561 nm single-wavelength laser output through theoretical analysis and experimental design,which were compared and analyzed by thoughtful experiments.The main research work is as follows:1.The research progress of 561 nm lasers in recent years has been investigated,and the related researches on volume Bragg gratings(VBG)for linewidth compression and wavelength tuning in different bands are summarized.2.The theoretical research and analysis of the single-wavelength laser output at 561 nm is carried out.Aiming at solving the difficulty of suppressing adjacent spectral lines beyond 1123 nm,two methods for suppressing the onset of adjacent spectral lines are proposed through theoretical analysis: the method of inserting F-P etalon into the cavity,and the method based on reflective volume Bragg grating(RBG)as both a frequency-selecting element and acting as an output coupling mirror.Theoretical simulations were carried out for the two proposed design methods respectively,provides a theoretical basis for feasibility experiments.In addition,in order to realize the compactness of the 561 nm laser structure,the resonator and the pump source are designed and optimized respectively.3.An experimental study of the single-wavelength laser output at 561 nm was carried out.Inserting the F-P etalon in the cavity,under the conditions of using an etalon with a thickness of 0.22 mm,a cavity length of 25 mm,and a pump power of 4 W,a single-wavelength laser output of 561 nm of 128.1 m W was obtained,and the power instability of 0.93% was obtained within 5 minutes.Using the RBG output coupling mirror method,under the condition of a cavity length of 25 mm and a pump power of 4 W,a single-wavelength laser output of 229.6 m W at 561 nm was obtained,with a power instability of ～2.98% within 5 minutes.4.Theoretical design and experiment of selecting single longitudinal mode using the combination of RBG and F-P etalon are carried out.By designing the parameters for frequency selection using the F-P etalon,the theoretical parameter values satisfying the selection of single longitudinal mode in combination with RBG were obtained.Combined with the experimental verification,it is concluded that the suppression effect of the F-P etalon on the multi-longitudinal modes in the cavity would become better with the increase of its thickness,which is consistent with the theoretical analysis.