Stable Second Harmonic Generated 461nm Blue Radiation Using An External Ring Cavity

Optical clocks became a new focus in the research of metrology from 2002.Time frequency shows great promise as the next generation of precision frequency standards and the uncertainty has arrived at the 10^-15level at present, promising to be even more accurate by optical clocks research.As the first step of laser cooling and trapping to atomic strontium,the ¹S₀-¹P₁ transition at 461nm laser is one of the important parts of optical clock research.This paper presents an external ring cavity for frequency doubling is used to generate 461 nm blue radiation,with PPKTP as a laser frequency doubling crystal.The signal of transmission laser is detected,and disposed by power locking system,then feeds back to the cavity,in order to realize that the output of 461nm is locked to the 922nm laser.And we calculate mode matching,Boyd-Kleinmen focus factor, enhancement ratio of cavity power,conversion efficiency,and so on.It is the first time that the cavity designed incorporated for enhance the power stability.Using this system, we have gotten more than 208mW of the second harmonic generation from 350mW IR input power.The coupling conversion efficiency is more than 70%.At the same time our system has great output steadily.And we discuss the effect of the coupling mirror with different reflectivity and PPKTP crystal's thermal lensing effect led by linear absorption to the conversion efficiency.