Study On The Dual-frequency Microchip Laser Spectrum Of LD Pumped

Diode-pumped microchip lasers combine many advantages, such as compactness, long lifetime,good stability, high efficiency and good quality. Have been found in a wide variety of applicationsin the fields of space optical communication, laser radar, precision measurement, non-linear optics,medical treatment and optical generation millimeter-wave. LD-pumped dual-frequency microchiplasers has lots of advantages with low threshold, large frequency-difference, high conversionefficiency, tunable and dual-wavelength stability, is very useful in the field of Radio-Over-Fibersystem, network communication system and laser precision measurement system. Therefore, inrecent years, LD-pumped dual-frequency microchip lasers has become a research hotspot of largefrequency difference dual-frequency laser.To get stable dual-frequency microchip laser can be used for optical generation microwavemillimeter wave source, this thesis mainly studies the spectral properties of dual-frequencymicrochip laser, theoretically and experimentally. The main contents can be summarized as follows:(1)An overview of dual-frequency microchip laser, introduced the research development ofLD-pumped dual-frequency microchip laser at home and abroad, the application in practice anddeveloping tendency of dual-frequency microchip laser.(2)The fundamental theory of LD-pumped dual-frequency microchip laser is analyzed, bymeans of rate equation of four-energy-level dual-frequency microchip system, the theoreticalanalysis and investigation of LD-pumped dual-frequency microchip laser’s working characteristicsare conducted.(3)A dual-frequency microchip laser model for generation dual-longitudinal mode isinvestigated. Firstly, the longitudinal mode generating mechanism of the microchip laser istheoretically analyzed; and then dual-longitudinal mode output is realized by using microchip laser,experimentally. The experimental results show, by tuning the current of pumping LD, the frequencydifference is variable within a certain range. With14.5A pumping current, a stabledual-longitudinal mode is output, and the frequency difference is85GHz. Increasing the pumpingcurrent, the frequency difference decreases gradually, with19.5A pumping current, the frequencydifference is53GHz.(4)A detailed study of the thermal effects of LD end-pumped the double longitudinal modesdual-frequency microchip lasers, and its influence to dual-frequency lasers spectrum. Throughsolving the heat conduction equation of isotropic material, a general expression of temperature field within Nd:YVO4microchip crystal was obtained respectively, then analysis the thermally inducedrefractive index changes of microchip lasers, and thus calculate the thermally induced frequencydifference changes of dual-frequency microchip lasers. Design experiments according to thetheoretical results, experimental results show that with a small pumping power, a stable doublelongitudinal modes dual-frequency is obtained; increasing the pumping power, the thermal effect ofcrystal make the frequency difference decreases gradually, and the width of each mode spectrumbroadening. The experimental results were well in agreement with the theoretical analysis.(5)A theoretical model of rate equations in dual-frequency pulsed microchip laser is presented.The self-saturation coefficient and cross-saturation coefficient, who close relate to the modescompetition effect are experimentally calculated as β=0.7and θ=0.3. Two polarization modescouple to each other strongly, and this results in an anti-phase relaxation oscillation. The relaxationoscillation waveforms peaks of two polarizations interlace to each other, and no waveform peakssynchronize. According to theoretical results, we shift the gain curve and resonance wavelengths foradjusting the relative gains of л and σ polarization modes, which offers an effective way to finelysynchronize the laser pulses of two modes under prepump mechanism. At last, a pair ofsynchronized dual-frequency pulse trains is achieved, with86GHz frequency separation and lessthan10ns timing jitter, which can be used as the input source of electrical beat note signal.