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Effects Of Thermally Induced Birefringence In Polarization Coupled CW Laser

Posted on:2005-01-24Degree:MasterType:Thesis
Country:ChinaCandidate:Y F YangFull Text:PDF
GTID:2168360152468496Subject:Physical Electronics
Abstract/Summary:PDF Full Text Request
Birefringence compensation in polarization coupled CW laser is proposed after theresearch about thermally induced birefringence. Experiments with E-O Q switch in CWlaser are carried out: (1) Temperature distribution, stress distribution in Nd :YAG crystal is analyzed withthe equation of thermal transmission, related curves are protracted. Temperature field isaffected seriously with pumping power, and improved when coefficient of thermaltransmission is added. The tendency of temperature field cannot be changed with thetemperature of cooling fluid, which could only decrease temperature in the surface of rod.Optical path length is 4 times of λ , when pumping power is 4KW. (2) A Nd :YAG laser rod under the thermal stresses from continuous pumpingbecomes optically anisotropy; specifically, the crystal becomes biaxial. The refractive indexdifference between radial and tangent causes a polarization rotation inside the optical cavityand at the polarizer hence a reflection loss, which belongs to 0.3 although different polarizemodel has different varied tendency. (3) Output power and optical quality are affected seriously by thermally induced stressbirefringence. Calculation of this loss for CW laser has been made and is compared toobserved decreases in output power, which is 2.1W with pumping power of 4 KW. A leakedlaser beam is observed reflected from one side of the polarizer. Beam pattern is a crosscircle with a bright dot in center. (4) Depolarization compensation is not obviously although which can be done with aquarter-wave plate. Such effect could be better in TEM00, but with small mode volume, alittle output power can be added. With model compensation, mode volume can be approvedwithout adding depolarization loss. The output power is 5W, with pumping power of 4 KW,two times than that of without compensation. (5) Experiment research with E-O Q switch and frequency doubling is given withmodel compensation, the pulse width of 66~69ns, peak power of 15 KW are achieved.
Keywords/Search Tags:continuous pumped Nd :YAG laserde, polarization loss thermally induced birefringenc, E-O Q switch compensation with a quarter-wave plat, model compensation
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