激光模拟器衍射损耗的研究

激光模拟器衍射损耗的研究 第 21 卷 第 3 期Vol . 21 ,No . 3 激光技术 1997 年 6 月J une ,1997 L A SER T ECHNOL O GY ΞStudy on diff raction losses of la ser simulators R ao J ion gh ui , Fa n g Q i w a n , J i a n g Ch u a nf u , Zha n g X i aoh ui ( )Naval Academyof Engineering , Wuhan ,430033 Abstract : The divergence p rovided by t he semico nductor laser are all defined at t he point of half power . In p ractical calculatio n , it must be t ransformed to anot her define level and t he measurement di2 vergence of L OC laser is rat her great . So t he t ransformatio n formulas of divergence for a Gaussian beam are modified in t his paper . According to t he modificatio n , t he formulas of diff ractio n losses of t he laser simulators are derived. As t he examples ,t he diff ractio n losses of t hree types of laser simulators are calcu2 lated. Key words : diff ractio n losses laser simulators 激光模拟器衍射损耗的研究 饶炯辉 方启万 江传富 张晓晖 () 海军工程学院 ,武汉 ,430033 摘要 : 半导体激光器给出的是半功率点处的发散角 ,在计算时必须进行变换 ,因实测 L OC 激 光器发散角较大 ,本文对高斯光束发散角变换公式进行了少许修正 ,导出了模拟器衍射损耗公式 , 并计算了三种模拟器的衍射损耗 。 关键词 : 衍射损耗 激光模拟器 1 . Introduction () () The GaAs2Al GaAs big p hotocavit y L OClaser is a new t ype appliance w hich develop s o n t he basis of t wo kinds of lasers w hich are single2difference2material junctio n and t wo2difference2 material junctio n . It has bot h t he advantage of t wo2difference2material junctio n lasers w ho se t hreshold elect ric current is very low and t he advantage of single2difference2material junctio n lasers w ho se o utp ut power is great . So we select t his kind of L OC laser as light so urces of several kinds of laser simulato rs. As t he o utp ut laser beam divergence w hich is p rovided by t he directio n to L OC laser is not very great ,t he diff ractio n lo sses are usually neglected in designing calculatio ns fo r laser simulato rs. But in f act t he o utp ut beam divergence of t he L OC laser is rat her great and t he laser t ransmissio n and t ransfo r matio n fo r mulas w hich are p rovided by general references can not be used indiscriminately. Thus t he diff ractio n lo sses of laser simulato rs are usually quite great and can not be neglected. 2 . The divergences of LOC la sers The divergence curves of t he L OC laser w hich is selected are show n in Fig. 1 . In Fig. 1 t he divergence parallel to p2n junctio n is 14?,and t hat no r mal to p2n junctio n is 20?. But measured in p ractice t he divergences are much bigger . The t ypical divergence curves L OC laser w hich are mea2 sured in p ractice are show n in Fig. 2 and Fig. 3 in w hich t he divergence parallel to p2n junctio n is 20?and t hat no r mal to p2n junctio n is 66?. But it must be noticed t hat t he above divergences can not be directly used in t he laser t ransmissio n fo r mulas fo r t he divergences p rovided by semico nduc2 θto r lasers are all f ar2field divergences w hich are defined at t he point of half power . That is 1/ 2 θθ 2= 20?,2= 66?. But t he divergences p rovided by general references are f ar2field diver2?,1/ 2 ?,1/ 2 2 θ gences w hich are defined at t he point of 1/ eof t he laser intensit y. Thus in o rder to apply laser t θθransmissio n fo r mulas must firstly be t ransfo r med into . 1/ 2 Fig. 2 The t ypical far2field pat tern of Fig. 3 The t ypical far2field pat tern of Fig. 1 The divergence angle of L OC laser L OC laser light beam 3 . Transf orma tion of divergences 2Acco rding to reference 1 t he fo r mula b y w hich t he divergence defined at t he point of 1/ e of laser intensit y is t ransfo r med into t he divergence defined at t he point of half power is ( )θ θθ1 = ln2/ 2= 0 . 5887 1/ 2 But t he aut ho r t hinks it can not be directly applied here . Because it is o nly applicable fo r Gaussian beam w hich is near t ransmit ting axis. But t he divergence of t he L OC laser can reach tens degrees. θθ () Thus it can not be co nsidered t hat tg=and eq. 1must be mo dified as ( )θ θθ2 = ln2/ 2 t g= 0 . 5887t gt g 1/ 2 θθθSubstit uting 2= 20?,2= 66?into above equatio n ,we can solve fo r 2= 33 . 3?, ?,1/ 2 ?,1/ 2 ? θ2= 95 . 6?. The divergences are so big ,if t he t ransmit ting antenna is not used to co mp ress t he ? divergences ,t he maximum range o nly reaches m o rders of magnit udes. Acco rding to reference 2 ()θ) ( α( )3 t he maximum range is Z= L / exp - Z/ 2 m m θ In o rder to meet wit h t he requirement of t he maximum reange , must be reduced t hree o r2 θders of magnit udes. The relatio nship amo ng t he divergence ,t he focal lengt h f of t he t ransmit2 ting antenna and t he laser’s maximum t ransmit ting lengt h l is as θ ( )= l / f 4 l is app ro ximate f ro m tens to hundreds micro ns ,and f is app ro ximate f ro m tens to hundreds millimeters. Thus f is quite lo ng . Wit h t he rest rictio ns of co st ,volumn ,and weight ,t he t wo2glued lens w ho se apert ures are not large are used ,w hich makes t he diff ractio n lo sses be very great . 184 激 光技术1997 年 6 月 4 . D iff raction losses The dist ributio n of t he energy2flowing densit y w hich passes t hro ugh t he Gaussuan beam w ho se diameter is D and radius is a is 3 22 2 2 2 2 ( )μμπωω) ω) ω) (( ( 5 S = = 2/ exp { - 2 [ x / + y / }x y x y The ratio T of t he power passing t hro ugh t he diameter D to t he total power can be derived 2 2 a/ 2 a/ 2 2π S 4 x y x y aθ ( + ) ]d x d y d- 2 T = = exp22 2 2 ???S 0 0 0 πωω ? x y ωx ωy 2 2 2 ( ( ) (ω) ω) ( )= 1 - exp { - D/ 4[ 1/ + 1/ } 6 x y We call ratio T as power t ransmissio n and define t he diff ractio n lo sses of t his apert ure as 2 2 2 ( ( ( ) ()δ ω) ω) 7 = 1 - T = exp{ - D / 4[ 1/ + 1/ } x y Apparently diff rac2 Table Diff ractio n lo sses fo r t hree t ypes of laser simulaters δtio n lo sses is related to Zωω δ f D a/ a/ T mt ypes ( )( )( )( )( )( )( )mm mm mm mm % % km relative diff ractio n aper2 navigatio n rocket 1 . 5 50 28 0 . 9563 0 . 2539 61 . 00 39 . 00 ωωt ure a/ and a/ . If x y navigatio n gun 3 . 0 100 50 0 . 8361 0 . 2267 52 . 79 47 . 21 t hese t wo relative aper2 6 . 0 200 60 0 . 5017 0 . 1360 23 . 69 76 . 33 chaser t ures are 1 ,t hen diff rac2 tio n lo sses are 13 . 53 %. The smaller t he apert ures , t he bigger t he diff ractio n lo sses. Now we list t he diff ractio n lo sses fo r t hree types of laser simulato rs and partial relative parameters in table . The experimental result s fo r t he maximum ranges of t hree t ypes of laser simulato rs are f un2 damentally co nsistent wit h t he datas in t he above table . Ref erence 1 周炳琨 ,高以智 ,陈家骅 et al . 激光原理. 北京 :国防工业出版社 ,1980 :350 2 ADA102276 ,Appendix B ( ) 于志文. 兵器激光 ,1986 ; 1:313 3 3 3 作者简介 :饶炯辉 ,男 ,1976 年出生 。在读硕士研究生 。主要从事军用光电技术的研究 。 收稿日期 :1995211209 ?产品简讯?N d?YA G 激光器 美国亚利桑那州 Power Technology 公司推出 D Y 系列 N d?YA G 激光器 ,该系列激光器设 计为宽温度范围运用 。内置温差冷却器自动维持苛刻环境中最佳输出时激光器的温度 。12V 直流电压装置适用 532 nm 波长 0 . 3 ,1 . 0 ,3 ,5 ,10 和 20 mW 输出 。轴向束校准和光束中心调整