The Research On High-power Single-frequency 671-nm Laser System

Lasers can be used to accurately probe and manipulate atomic and molecular sys-tems.They promote a rapid development of ultracold atomic physics which becomes an ideal platform for quantum simulation.Lithium atoms are one of the most important research species in ultracold atomic experiments,because it has light weight,simple structure and fermionic and bosonic properties of isotopes.They are suitable to use Feshbach resonance for manipulations.Efficiently cooling and trapping lithium atoms usually require Watt-class lasers at 671 nm.Higher requirements up to multi-watt 671-nm output come from decreasing the temperture of sub-Doppler cooling and increasing the number of atoms in high efficient evaporative cooling.In addition,one can build up superlattices using 1342-nm laser and 671-nm laser to manipulate ultracold atoms.To meet urgent demands of high-power 67nm lasers for ultracold atomic experi-ments,we implement and develop a 671-nm laser system,and achieve the high-power continuous-wave single-tunable-frequency,narrow-linewidth 1342-nm laser and 671-nm laser,with good stabilities for applications of ultracold atomic experiments,by solving difficulties,such as thermal effects of the crystal and high-power frequency-doubling technique.This thesis mainly includes the following three parts:In the first part of the thesis,for realizing high power all-solid-state single-frequency tunable 1342nm laser,thermal effects of the laser crystal Nd:YV04 was investigated.Based on theoretical analysis,the crystal thermodynamic simulation models were es-tablished and thermal focal lengths were measured.We investigated the way for reduc-tion and compensation of thermal lens effects of crystals,and we used a pump laser at 888 nm,a three-segment-doped crystal with low temperature,and a meniscus cavity mirror to compensate for thermal lenses.Then,we employed a Faraday isolator,two etalons in a ring configuration to obtain a single-frequency operation of high-power laser.The laser frequency tuning function is realized by the combination of thick and thin etalon and PZTs.Finally,a single-frequency tunable 1342-nm laser output up to 11 W is achieved.In the second part,for realizing high-power 671nm laser from high-power 1342-nm laser,the high-power high-efficiency frequency doubling is investigated.We chose to use the extra-cavity as the scheme and PPKTP as the nonlinear crystal.Based on studying thermal effects of PPKTP,we enlarge the beam waist in PPKTP and shorten the length of PPKTP for a focusing parameter,to minimize thermal dephasing and thermal lensing.Good impedance matching and mode matching is obtained.Finally,a 5.2-W 671-nm laser is achieved a with a conversion efficiency up to 93%.In the last part,for the requirement of laser stability in ultracold atomic experi-ments,and the requirement of optical lattice for narrow linewidth,the laser system fre-quency stabilization technique and linewidth narrowing technique are researched and analyzed.To improve passive stability,the prototype of 1342-nm laser and 671-nm frequency-doubling cavity are designed and implemented.The HC frequency locking for the frequency-doubling cavity and the PDH frequency locking for the 1342-nm laser are realized.With using an improved cascade PDH loop and an narrow-linewidth ultra-stable cavity,the linewidth of the 1342nm laser below to sub-kHz-level is achieved.The key innovations points are listed as follows:1.To solve thermal-effects problems in Nd:YV04 crystal which limit the power of 1342-nm laser,we use 888-nm pump laser and design a multi-segmented Nd:YV04 crystal and a thermal-compensating cavity to achieve 11-W high-power single-frequency all-solid-state 1342nm laser.2.To improve frequency conversion efficiency in high-power operation with PP-KTP,we propose a scheme that using a short crystal and a large beam waist for reducing the thermal effects effectively.The scheme causes a optimal focus parameter which is far away from the theoretical vaule.The conversion efficiency is improved up to 93%and a 671-nm laser output of 5.2 W is realized.3.One-box configurations are realized for principle prototypes of the all-solid-stae laser and the frequency-doubling cavity,and the passive stabilities of principle proto-types are improved.By using the cascaded PDH locking technology and the narrow-linewidth ultra-stable cavity,the linewidth of the watts high-power laser is narrowed effectively down to 1 kHz-class.