Nguyen VSn Hao vd Dtg Tgp chi KHOA HOC & CONG NGHE 135(05): 173-1I77
SU^ D U N G P H I N L Q C L U ' O f N G C H I E T T R O N G C O N G N G H E L A S E R Nguyen Van H a o ' ' ^ ' , P h a m Hong Minh^
' Tru&ng Dai hoc Khoa hoc - DH Thdi Nguyen ' Vien I 'dl ly. Viin Hdn ldm Khoa hoc va Cong ngh? I 'lei Nam T O M T A T
Chung toi trinh bay c^c ket qua nghien cihi \k viec su dung phin loc luong chiet nhu y^u to chpn Ipc pho trong buong cpng hudng laser, dac biet trong cac laser phat xung ngan. Cac nghien cuu n^y duoc thuc hien tren nhffng laser rSn nr ngoai Ce:LiCAF (280 - 320 nm) va laser rdn h6ng ngoai C r L i S A F (780 - 900 nm). Cac ket qua nghien cihi thu duoc khong chi cho chiing ta hieu biet dugc dpng hpc ciia q u i trinh lam hep phfl trong phat xa laser bang hep m^ con chi r5 cac dac diem khi viec siJr dung phin lpc ludng chiit nhu yiu t6 chon lpc ph6 trong cong nghe laser.
Tfr kh6a: laser cue ngdn, phin lpc lu&ng chiet. laser don sdc, laser ran M O D A U
Phin Ipc l u o n g chigt B F (birefringent plate) la mpt ySu to di6u chinh b u a c song d u g c sir dung rpng rai trong cac laser [1-5]. Tam BF t h u a n g d u p c dat trong mpt buong c o n g h u a n g ( B C H ) laser a goc Brewster va b u a c song d u g c thay d6i n h a s y q u a y cua tSm BF quanh phap tuyen, Uu diem cCia phin Ipc nay la dp tan sac cao, mat mat thap va kha n a n g chong hu hai it cucmg dO cao. T r o n g rSt nhi^u ung dung ciia c 6 n g ngh^ laser n h u : thong tin quang, chup X - q u a n g kkx hpp, hien anh q u a n g hpc y-sinh, kiem tra thiet bj q u a n g hpc, giao thoa nguy8n tu, q u a n g pho hpc va t h | m chi la ki6m tra ky sinh trung trong n u d e [6-9]...thi cac laser d a n t i n (c6 dp d o n s4c cao) co mpt vj tri v o Cling quan trpng. Phin Ipc l u d n g chi€t la mpt y i u to chpn Ipc pho d u a c sir d u n g rpng rai nhat trong c o n g nghe laser, d a c biet la laser x u n g ngSn d^ phat nh&ng biic xa laser co dp dcrn sac c a o trong viing s o n g tir t u ngoai toi h d n g ngoai. T r o n g n h u n g laser x u n g ngan, laser tCr ngoai C e : L i C A F va h d n g ngogi C r : L i S A F [10, 11] la cac laser c 6 pho phat xa rpng, d o d o n o c o the phat d u p c cac x u n g ng^n va pho h? p khi sir d u n g t i m B F trong budng c p n g hucmg.
T r o n g bai bao nay, b a n g vi?c d u a them mpt hoac nhi^u tam phin Ipc l u o n g chiet vao trong b u o n g c p n g h u a n g laser, c h u n g toi dS nghien
c u u d u a c tucmg minh kha n a n g phat cac buc xa d o n sac ciia chiing d u a tren cac tinh toan ly thuyet n h o sir d u n g h e cac p h u a n g trinh toe dp m a rpng cho nhieu b u a c song [11-13].
PHIN L O C L U ' O N G C H I E T
Mot tam BF don true d u g c sir d u n g n h u mpt yeu to dieu chinh b u o c song t h u d n g d u o c dat trong BCH laser d goc Brewster. Anh sang phan c u e d u o c truyen qua mpt phin Ipc bi taeh thanh hai tia thucmg va dj t h u d n g boi hieu umg l u o n g chiet cua tinh the thach anh.
Ham dieu chinh b u d c song (truyen qua) cua mpt t a m B F d u g c d u a tren dac trung giao thoa su phan c u e ciia no va d u g c bieu dien theo c o n g thiJrc sau [14] :
T - 1 - 4 c o t - 7tan^ 6i(l - c o t ^ yiar\- e)sm- - ( I ) trong d o , G la goc tdi (goc B r e w s t e r ) , ; ' la goc g i u a tia khiic xa va true q u a n g hpc va S la dp lech pha giira tia t h u d n g va di t h u d n g trong tam B F . 5 n h u la mpt ham cua dp day d cua tam BF, hieu chiet suat giiJa tia t h u d n g va di t h u d n g ciia tSm, goc ^ v a b u d c song laser.
G o c dieu chinh b u a c s o n g A d u g c dinh nghTa la goc giira mat p h a n g tdi va mat p h a n g d u g c xac dinh bdi true q u a n g hpc va phap tuyen ciia B F [14].
cos/-sin^sina
cos A = (2)
' Tel: 0989 348258. E-mail. haonv@tnus edu vn
cos ^ c o s a
d day, a la gdc giCra true q u a n g hoc va be mat ciia tam B F .
173
Nguyin Van Hao vd Dtg Tgp chi KHOA HOC & CONG NGHE 135(05): 173-177 Vdi mpt tSm BF cu the, chiing ta co the ve
dugc cac dudng cong truyen qua nhd sir dung bieu thirc (1) tren may tinh. Khi sir dung nhifiu tam Ipc ludng chiet thi dp truyen qua cua he se la tich so cua do truyen qua cua tiing tam. Tuy nhien, ti s6 dp day r ciia cac tam nay phai ia cac s6 nguyen va bk mat cung nhu true quang hpc ciia chiing phai dugc dat song song vdi nhau.
T = T^xTjxT^x T„ (3) KET QUA VA THAO LUAN
Dudng cong iruyen qua cita ldm BF Hinh 1 chi ra dudng cong truyen qua cua mpt tam BF vdi dp day d = 0,4 mm va d goe dieu chinh budc sdng A = 41°; or = 0 trong dai sdng rpng keo dai tir viing tu ngoai tdi vimg hong ngoai gan. Ket qua cho thay, bang viec quay tam BF quanh true quang hge ctia nd, chung ta cd the chpn dugc dinh sdng truyin qua phii hgp vdi dai sdng can dieu chinh cua laser.
300 400 500 600 700 800 900 1000 Bircc song (nm)
Hinh I. Dicang cong truyen qua ciia phin lpc lu5ng chiet dan tdm v&i do ddy d = 0.4 mm vd goc quay A^ 41"; a^ 0 trong ddi song tic viing
tu ngoai t&i viing hong ngogi gdn.
Hinh 2 bieu dien dudng cong truyen qua cua mpt va nhieu tam BF vdi ti sd do day khac nhau trong dai sdng tu 750 - 950 nm. Ket qua cho thiy, vdi dp day nhu nhau cua moi tim (d
= 0,5 mm) d ciing mpt gdc diiu chinh budc sdng A = 41,7*^ nhung khi sd lugng phin Ipc nhieu hon thi phd budc sdng cd do titiyin qua cue dai se hep han. ddng thdi cac cue tiiu truyen qua xuat hien gSiT nhau han va cung cd cudng dp nhd hon.
Bo'i vdi cac laser dieu cljinh budc sdng, s€ cd mpt dai budc sdng cd the truyen qua tSm phin 1741
lpc (dp truyen qua cue dai), khi do de thu dugc birc xa laser cd budc sdng mong muon, chiing ta cd the sii dung nhi6u tim phin lpc dat sat nhau trong budng cpng hudng.
750 8C» 850 900 950 Birerc song (nm)
Hinh 2. Du&ng cong truyen qua cua nhieu tdm phin lpc lu&ng chiet v&i do day khde nhau & gdc dieu chinh bu&c song A = 4l"; a = 0; d- 0,5 mm vd v&i ti le dp ddy cdc tdm Id r = 1; 1:2; 1:2:4;
1:2:4:9 trong ddi song tir 750- 950 nm.
Laser ran bdng hep sir dung phin Igc lu&ng chiet Hinh 3 la cau hinh budng cpng hudng cho laser ran dupc bom bang cac xung laser diode. Buong cpng hudng laser gdm-hai guong, trong do M| la guong bom - guong cau cd dp phan xa rat cao va M? la gucmg ra cd dp phan xa thip hem. Tinh thi laser la mpt tinh thi rin (Cr:LiSAF va CeiLiCAF) dugc dat trong budng cpng hudng sao cho co dugc su chong chdng tdt giiJa mode bom va mode laser. Trong boat dpng laser bang hep va diiu chinh Hen tuc budc sdng, chiing tdi da dua them vao trong BCH mot hoac mot vai tam BF dugc dat dudi gdp, Brewster.
M l M ,
"-.i h Tmh th^ laser Cac^.tam BF Hinh 3. Cdu hinh laser rdn bang hep su dvng phinn
loc lu&ng chiet BF dgi Irong buong cong.hu&ng, ^(i L, vd L2 Id he bam; Mi Id guong laser cuqi vd Mi, Id guang laser ra Moi tru&ng laser co th^'ld-liiiff'
thi Cr-LiSAFhodc Ce.LiCAF. J: ': ;i'.fl Hinh 4 biiu diln phd laser Cr:LiSAF bang'' hep tren dai sdng tir 835 - 865 nm khi sir dung mgt tam phin Igc ludng chiit day d = 1
Nguyen Van Hao vd Dig Tap chi KHOA HOC & CONG NGHE 135(05): 173-177 mm, a - 0, gdc dieu chinh budc sdng A thay
ddi tir 39,9° - 43,5" dat trong budng cpng hudng laser (nhu Hinh 3) vdi he sd phan xa ciia cac guong R, = 1, R3 = 98 %; chiiu dai tinh the laser 7 mm, ndng dp pha tap ion Cr^*
la 1,5 % d cdng suit bom P = 1,5 W, dp rpng xung bam 100 ps; ban kinh vet bom rp = 22 pm. Ket qua cho thay, vdi mdt tam phin lpc cd dp day khdng ddi, nhung dugc quay vdi cac gde A cd gia trj tang din thi buc xa laser Cr:LiSAF c6 dinh budc sdng djch chuyin ve phia sdng dai.
mm dat trong budng cdng hudng laser cd he sd phan xa cac guong R| = I, Rj = 99 %;
chieu dai tinh the laser 7 mm, ndng dp pha tap ion Cr'* la 1,5 %, tim BF d gdc a = 0, gdc dieu chinh budc sdng ^4 = 41,7° vdi cdng suat bam P = 1 W, do rpng xung bom 100 ps; ban kinh vet bom rp = 22 pm . Khi dp day cua tam phin Ipc ludng chiet d = 1 mm thi phd laser dugc lam hep tdi 0,25 nm.
840 850 855
By&c song (nm) Hinh 4. Pho laser CrLiSAF bdng hep tren ddi song tir 840 - 860 nm khi su dung mpt tdm phin
lpc lu&ng chiet ddy d= 1 mm dgt trong buong cpng hu&ng laser, a= Od goc dieu chinh bu&c
songA thay d&i tit39.^^-43.5".
Hinh 6.Suphif thuoc do rpng pho phdt xg laser tu ngoai Ce:LiCAF vdo dp ddy ldm BF: (a) d = 2
i.(b)d = 5mm (c) d^ 10 mm. (d) d^ 12 mm.
BCHvaiL=10 cm, R, = 100%, R2 = 30%; cm, mat dp ion Ce' N = 5xl0"'
0.15 cm va A ^55.4
Hinh 5. Qud trinh ldm hep pho Irong laser Cr' . LiSAF bdng hep khi su dung phin ipc lu&ng chiit c& dp ddy d thay ddi tir 0,1 -^^ I mm ddt trong
budng cpng hu&ng laser, a^OvdA ^ 41,7.
Hinh 5 la tiin trinh lam h?p phd cua laser Cr:LiSAF bang hpp khi sir dung phin Ipc ludng chiit cd dp day d thay ddi tu 0,1 -^ 1
Hinh 7. Dong hpc pho 3-D trong phdt xg laser tu ngogi Ce:LiCAF bdng hep v&i goc dieu chinh thay
ddi- (a) A = 55", (b) A = 55.2". (c) A = 55,4". (d) A = 55.^. (e) A - 55,^vd (f) A ^ 5^. BCH v&i chiiu ddi L = 10 cm. R, - 100%. R, = 30%; mat
dp ion Ce' N = 5x10'" cm''; ndng luang xung bom Ep- 17 mJ. r^ = 0.15 cm vd dp ddy tdm BF
lad ^ 10 mm.
Hinh 6 cho thay su phu thupc dp rdng phd phat xa laser ran Ce:LiCAF vao dp day tam
Nguyen Van Hao va Dig Tap chi KHOA HQC & CONG NGHE 135(05): 173- 177 phin lpc ludng chiet d cac dp day khac nhau d
= 2 mm; 5 mm; 10 mm, 12 mm, Hinh 7 la ddng hpc pho 3-D trong phat xa laser tir ngoai Ce:LiCAF bang hep vdi gdc quay A thay ddi tir ^ = 55° din A = 56°. Kit qua cho thiy, laser ran tir ngoai Ce:LiCAF cd dp lam hep phd thap hon so vdi laser ran Cr:LiSAF. Dieu nay cung de dang giai thich khi ta chu y tdi thdi gian sdng di lai cua photon trong budng cpng ciaa hai laser la rat khac nhau, do thdi gian sdng huynh quang ciia Cr:LiSAF ldn hon Ce:LiCAF hang 1000 lan [10, 11].
KET LUAN
Bang vice sir dung cac phin lpc luang chiet nhu mpt yeu td chpn Igc phd trong budng cong hu'dng laser, dac biet trong cac laser phat xung ngan chiing tdi da nghien ciru dugc dpng hpc lam hep phd cua cac laser ran til ngoai Ce:LiCAF va laser rin hdng ngoai Cr.LiSAF. Cac ket qua cho thay tien trinh lam hep phd trong cac laser ran phu thudc vao cac dac trung cu the ciia cac tam phin Ipc luong chiet cung nhu cac tinh chat quang ciia mdi trudng laser.
L&i cdm on: Cac tac gia tran trong cam on su tai trg kinh phi tir De tai KHCN cap Dai hoc cua Dai hoc Thai Nguyen (mii s6 DH20I2-TN07-I3).
TAI LIEU THAM KHAO 1. G. Holtom and 0. Teschke, "Design of a birefringent filter for high-power dye lasers," IEEE J, Quantum Electron. QE-IO, 1974, pp.577-579.
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pp 501-504
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Bouyer, "Dual-wavelength laser source for onboard atom interferometry," Opt. Lett. 36, 2011, pp. 4128^130.
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10. U Demirbas, S Eggert, A Leitenstorfer, Compact and efficient Cr: LiSAF lasers pumped by one single-spatial-mode diode' a minimal cost approach, JOS A B 29 (8), 2012, pp. 1894-1903.
11. Pham Hong Minh, Nguyen Phan Nhat, Do Quoc Khanh, Nguyen Dai Hung, Luong Viet Mui, Nobuhiko Sarukura, Liudmila Astafyeva, Investigation of the specfral and temporal processes of all solid state ultraviolet Ce^"^:LiCaAIF6 laser emissions. Advances in Optics, Photonics, Spectroscopy & Applications VI1, ISSN 1859 - 4271, 2013, p. 419-424, 12. P. Juramy et al., Specfral properties of pulse dye lasser, IEEE J, Quantum electronics. Vol QE- 13. No 10, 1977, pp. 855-865.
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H., Generation of tunable subpicosecond pulse using low-Q dye cavities,/ipp/. Opt.3\, 1992, pp.
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Nguyen v a n Hao vo Dtg Tap chi KHOA HOC & CONG N G H $ 135(05): 173 - 177
S U M M A R Y
B I R E F R I N G E N T F I L T E R U S E D I N L A S E R T E C H N O L O G Y
Nguyen Van Hao'"^*, Pham Hong Minh^
' College of Science - TNU - Institute of Physics. Vietnam Academy of Science and Technology We present the results of research on the use of birefringent filter as a spectral selector in the laser cavity, especially in the short-pulse lasers. The study was carried out on the tunable ulfraviolet solid-stale Ce:LiCAF (280-320 nm) and infrared Cr:LiSAF (780-900 nm) lasers. As a result, the obtained results showed clearly the dynamics of spectral narrowing in narrow-band laser emissions, and therefore, provided better understanding of the solid-state lasers in broadband and tunable laser operations. Additionally, it is also indicates the characteristics when using birefringent filter as a specfral selector m laser technology.
Keywords: ultra-short laser, birefringent filter, monochrome laser, solid-stale laser
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