Bo giao due va dao tao
Truong dai lipc Tong hap Ha ncn
vO TUAN LAM
ITRO CUA HIEU UNG TAO HOC VA SU PHU THUQC
HOI G I A N T R O N G H O A T D Q N G CUA LASER CHUA
VAT LIEU HAP THU BAO HOA
Cluiyen nglianh
:
Quaiig lioc
Ma hieii
:
1.02.18
Liian an Pho tien si khoa hoc Toan-Ly
tJgirai liunng dhn klioa hoc : Pho giao su Tien sT
Dinli Viin Iloang
lla no! - 1993
^
Myc Lvc
Trang
Md dau
^
Childng I: Anh hUdng cua
buong c^ng
hi|u -ing t^c hoc
hUdng
Fabry-Perot
trong LSA vdi
va
5
hi^n tUtpng
liidng on c^nh quar^g Y.QC .
.1-
Hi^n t\10n£ lUdng on dinh guang hgc
va cac hi^u Ung
5
vat ly phi tuyen trong LSA.
.2-
^^^
Anh huong hi^u Ung t^io hoc.
ChUdng II: Cac
d^c trUng
cua LSA
vdi buong cgng huong
IS
Fabry-Perot
. 1- Ke phtiong trlnh cd ban
1^'
.2- Anh hUdng cua hi^u ilng t^c hoc
trong ho^t cipng ddn
23
mode cua laser.
2.1- D|LC trUng ciidng dq) mode.
24
2.1.1- Toe d^ bdm nang lU';;^ng d hai ngan la khiong dbi.
25
2.1.2- Toe dr-
25
bdiL nang
luv^n£ ngan
khuyech d^,i
hhong
ieu
i^-j r ^
L
V"-i t r c
hudng
cua r.ieu
iln^ t a c
h
Fabry-Perc-
b'ac X9 tv- clgng.
- •"•
li j-"^!.!
L i^'^'j.i£.-,
Ci o
e n
'^ ^ i i i .
„•_ W..1I5
1 1 ' . 1^ -
'-* V • ' i r -
—<=• JiJ - ' O c
laser.
o »i." i.-'ac "crun^ c u c n g u-^ iriooe.
0.1,
j.^
iGC: Gp odrn r^ang lU^jng o n a i n ^ a r , a-a jiriong G^^'J. .
i ' c c d9
tdm ne^ng
I'jidng r . g a r
aeu.
Vai t r c
c u a b u c y.^
t\i
ddng.
•i~ -C'c ciV' '-•''-'n"i n a n g j.uo:ig c n a 1 lige,:': ^6. iincr.P; UC 1
3.2.2- Toe dp
bdir, nang
lUgng ngan
khuyech d^i khong
51
•deu.
3.3- D6 rgng' cua trUdng laser biie x^
GhUdng III: Ki^n
tuging hon
lo^in quang
53
trong ho^t dpng
58
khong d^ahg cua LSA
3.1- Ho^t deng khong dung
cua h^ LSA
trong che dg
ddn
SI
che dg da
G4
mode.
3.2- Ho^t dpng
khcng dUng
cua he
LSA trong
mode.
Ket lu^n chung
Phv luc 1
Phv luc 2
Phv luc 3
.
•
72
-
- 7 5
•
••
"6
•
80
Phu luc 4
PI
Phv luc 5
Tai li§u tham khao
-
8
6
6S
MO ^"'u r\ u
Trong nhUng
nam
gan
laser, cac nha khoa hoc
day, trong
llnh
chu y nhieu
vrlc nghien
den laser co
CLIU
chUa v|Lt
li^u hap thu bao hoa ( laser with saturable absorber,
tat la LSA ). LSA ra ddi t\i nhUng nam
A.SZOKE [ 116 1 la ngudi dau
phi tuyen ludng
on dinh
viet tat la OB ), Tu do
60
mdt hu6ng ung dyng mdi
muc dich giai thich
cac tinh chat vat
thu
cua
ngxJdi ta con tim ra nhieu hi^u ung
loan
quang ',' chaos ') , phan
trong quang
ciju ve LSA xuat
hien ngay cang nhieu nham
ly
hieu
( Optical bistability -
hoc phi tuven ra deli. Cac cong trinh nghien
ly
viet
cua thap ky nay.
tien da phat hien ra
quang hoc
ve
va khai thac
loai laser nay. Vdi LSA
phi
tuyen khac
:
hon
nhanh ( bifurcation i, tao xung
c\lc ngan .-. .
Co ba phiiong phap Ly thuyer- chinh de i;iai quvet bai
toan
quang hvc cua LSA.
Phudng phap thU nhat
la
phudng
phap ban co ciien. Trong
phUdns pha.p nay tr^idng dUoc xem la trudng
co dien tuan theo
cac phudng trinh dien dong
con he
lUc Maxwell,
cua moi tri.tdng tuan theo cac nguyen ly
Saloma va Stenhom
[107,108]
[32,331 da sU dung
phUdng
laser co md rong
cung
phap
khong dong
nguyen tu
cua cd hoc lUdng tU.
mot
Lamb
so
tac
gia
khac
trong trUdng yeu vcJi
nhat trong
hoat dong
cua ddn
mode.
PhUdng phap thU hai de giai
lugng tu. Trong phUdng phap
bai toan
LSA la phUdng phap
nay ca trUdng
va h^ nguyen
^6i truSng deu tuan theo cac nguyen ly cua cd hpc
tU
lU
Lugiato va Mandel [84] da bUdc dau nghien c{iu he LSA v6i moi
trUdng md rgng dong nhathoat dong d
che
do
ddn mode
bang
cUu
la DhUdng phap gan
phUdng phap lu^ng tU.
PhUdng phap
thU ba
dung he phudng trinh toe
dUdc nghien
do. Cac tae
cac phUdng trinh mo ta sU thay doi
gia [10-13] xay
dUng
theo thdi gian so photon
trong buong
cgng hudng,
sU thay
mUc nang lUdng trong cac
doi hieu tich luy . d cac
moi trUdng khuech
dai va hap
thu
theo cac thong so cua moi trudng nhu : bdm khuech dai, he so
tich thoat, do md rong vach nguyen tU...
De xay dung
dun.g
he phudng
trinh toe
do
ngUdi ta thUcJng sU
. hai phUdng phap khac nhau :
gian tiep. PhUdng
tiep la
.xac dinh phUdng trinh
tren ed sd nhUng qua trinh vat ly anh
hUdng den sU bien doi
eua moi trudng phi tuyen va anh sang.
RoLand va MuLLer [97]
va cae tac gia
phap trUe
true tiep hoi=LC
da sU
Laser da mode vdi
dung phUdng
md rong
dong nhat.
dung til he cac phudng trinh
trinh tec d$ mgt each gian
mot cong :*u de cu r.he
2 mUc
la phUdng phap xac
da nghien cUu
eUu vdi
ba phUdng
dong cua
lueng eho
cac ngan
hUdng dang vong
hay
trong cac tai lieu
Laser co
nhat la chu yeu. Con Laser vdi md rong
no nhU
sU sU hoat
mue nang
voi buong cong
la nghien
dinh phudng
Tren cd sd
buong cong huong Fabry-peroi:. Tuy nhien,
cong bo, hau het
suv ,gan
d trUdng hOv nay
tiep,
hay 4
khuyech ilai va hap thu
khi nghien cilu
PhUdng phap
hoa ly thuyet.
phap nay. nhieu tac gia
LSA vdi mo hinh
phap nay
md rong dong
khong dong nhat dUdc
nhien cUu chu yeu voi orudn.g hop don mode. Phan Ngoe Ha [10]
nghien eUu vdi
Laser khi vdi buong
Trong ban luan an
phUdng trinh toe
nay,
dg de
chung
nghien
cong hUdng dang vong.
toi
sU
cij(u hoat
buong cong hUdng Pabry-perot co
dung gan dung h^
dpng cua LSA
do md rong khong
la chu yeu. Cac van de dat ra eho luan
dong nhat
an la nghien cilu dac
trUng cUdng do bue xa va
dieu kien xuat hien lUdng
quang hoe trong
vdi buong
cac LSA
Qua do, xet vai tro eua hieu
cua LSA. Chung toi tim hieu
dong nhat den dac trUng eUdng
vdi
on dinh
cong hUdng Fabry-perot.
Ung tao hoc doi vdi
anh hUdng cua d^ md
hoat dong
rong khong
do bijlc x^i va dieu ki^n
xuat
hien OB.
De nghien
cilu dae trUng' cUcJng do mode bi-tc xa,
chung toi
xet hoat dong cua LSA trong che do ddn mode va da mode.
Ban luan an nay gom 3 ehUdng :
ChUdns I : ChUdng nay gom hai phan.
Phan 1 gidi
thieu qua
mot so
hieu Ung
LSA va trinh bay hien tUdng lUdng on
phi tuyen t.rong
dinh quang hoc v6i
cd
che va dieu ki^n xuat hien. Trong phan nay co dUa vao mot so
ket qua thUc nghiem hien tUdng
quan sat dUdc
lUdng
khi tien hanh thi
Phan 2 gidi thieu vai
on dinh ma chung
toi
nghiem v6i Laser khi Ar.
tro eiia hieu
itng tao
hoc trong
hoat dong eua LSA vdi buong cong hUdng Fabry-perot.
ChUdng II : Gom ba phan
Phan dau khao sat Laser khi ehUa vat lieu hap thu bao hoa
trong buong cong hudng Fabry-peroi: vdi mo hinh hai muc
iUdng. De mo ta hoat dong eua he,
nang
chung ~6i su dung phUong
phap he phUdng trinh toe do, vdi phudng phap nay,
xay dung dugc he phuong trinh dae "crung
c\ldng
chung toi
do mode
cua
d cac
ngan
laser khi eiing nhU sU thay doi hieu do tich luy
khuech dai va hap thu. Tiep theo chung toi si dua he phudng
trinh dac trung ve d^ng thuan tien eho tinh toan.
Phan thu hai khao sat hoat dong cua LSA vdi che
do
mode qua viee xac dinh dae 'rUng eudng do mode d trang
dilng. Tiep theo
nghien euu
trong LSA vdi buong
cong
sat sU bien doi
eudng do
ngan khuech dai
va hap
tUcpng lUdng on
dinh
vai
hUdng
bue xa
tro cua
Fabry-perot
khi thay
thu trong
quang
hoe
hieu ung tao
thai
hoc
qua viec khao
doi vi
buong cong
va
ddn
tri cac
hUdng. Hi|n
dieu kien xuat hien OB
dude de cap tdi trong trUdng hdp cu the.
• Phan thu ba khao sat hoat
khi thay doi toe
do bdm
nang lUdng
khong chi CO hien tUdng lUdng
da on dinh xuat hien. Moi
dong eua LSA d one
moi trUdng
on dinh ma eon
quan he giUa
do da mode
khuech dai
co hien tUdng
eUdng do mode
phat
va do rong trUdng bUe xa dUde xac lap.
ChUdng III: Khao sat hoat dong khong dung
eua he LSA chu
yeu vdi buong cong hUdng dang vong. Nghien cdu sU phu
thuoc
th6i gian eua cUdng do mode phat va hieu do tich luy cua hai
- 4 moi trUong. He phudng trinh
phapsotren cd sd
thuat
toan
trUdng hdp ddn mode va
dong cua he trd
nen
toe
do dUdc giai
Runge
Kutta
da mode. Vdi che
hon
lo^n
bang
ap
phUdng
dung chg cac
do da mode,
hoat
sau trang thai dilng,
hi^n
tUOng hon lo^n quang xuat hien.
Phan cuoi cung la ket luan, phu luc va tai li^u tham khao
Ban luan an nay cd ban dUdc hoan thanh tai bo mon
pho khoa vat ly trUdng dai
sung tai to vat ly dai
khoa ^/at ly trUdng
hoc Tong hop Ha
cUdng va cae
noi
quang
va dUdc bo
qua trinh truyen
song
d.ai hoc Tong hdp Matxcdva.
Cac ket qua eua luan an da dUde bao cao d
cac xemina tai
bo mon quang pho khoa vat ly trudng dai hoc Tong hdp Ha noi,
tai hoi nghi vat ly ly thuyet toan quoc Ian thil 12,13 [5,6],
tai hoi nghi quoc te mang ten
Jena-CHDC Due va
hoi nghi
Ernsrabe
quoc te
trien trong dien tu hoc lUdng tu
Ian
ve
thU
nhat
tai
nhung xu hUdng phat
d Bucares-Rumani[49,50] va
da dUdc cong bo d cae tap chi trong nUdc
[4,5] va tap chi d
nUdc ngoai [13].
, ,Nhan dip nay chung toi
doi vdi pho Giao sU,
.xin bay to
Tien si
dan khoa hoc- aa tan tinh
long biet dn
Dinh Van Hoang-
giup dd chung toi
sau sac
ngUdi hUdng
hoan thanh ban
luan an.
Toi cung xin bay to long biet dn sau sac doi vdi pho Giao
sU Krindash rdai hoe Tong hdp Matxccjva) , pho Giao sU Vu
CUdng, pho Tien
si Trinh
va CO nhieu y kien
co
Dinh
gia
tri
Chien da
de
tan tinh diu
NhU
dat
chinh ly va hoan chinh
luan .an.
Chung toi xin chan thanh cam dn cac Giao sU,can.b6 giang
day bo mon quang pho Dai hoe Tong Hdp Ha Noi co nhieu y kien
quy bau khi thUc hien de tai.
Chung toi cung xin chan thanh cam dn ban chu nhiem
vat ly va cac ban dong nghiep
xa gan da
tao dieu
khoa
kien vat
chat va tinh than oho chung toi hoan thanh luan an nay.
ChUdng I: ANH HUONG CUA HI?U L/NG
BUONG CONG
HUONG
TAG HOC TRONG LSA
FABRY-PEROT
VA
v6l
HI?N TUONG
LUdNG ON DINH QUANG HQC
1-Hi^n tUdng lUOng on dinh auans hnn va cac hJeu (Ang vat
]y ph-i tuven trong LSA.
Laser chUa vat lieu hap thu bao hoa fLSA) trong nhUng nam
gan day da trd thanh moi quan tam Idn eua cac nha vat ly
thuyet va thue nghiem. Cac
nha nghien eUu
da thu
ly
dUde mot
loat cac hien tUdng ly thu va md ra hu6ng (ing dung mdi trong
cac nghanh quang pho hoc Laser. Cac hien tUdng nay cung
nhU
Ung dung cua ehung da dude Phan Mgoc .Ha, Tr.an Thi Thu Ha [2,
3] trinh
bay trong
ban luan
an eua
minh. 0 day ehung toi
chi nhac lai nhUng net chinh va gi6i thifu mot so cone trinh
trong nhUng nam gan day eo lien :3uan t6i chung. Cac hifu ring
phi tuyen lien quan T:di LSA la:
1.1 Su bien
dieu
do
pham
chat
tiiiu
doug
(Passive
Qswitching- viet tat la PQS)
Day la mot trong nhUng
hien
tUdng dac trUng
Theo cac nha nghien cUu [14,13],
moi trUdng co he so hap
chat
thy ty 1§
eua
LSA.
hap thu bao
hoa la
nghich vdi cUdng
do anh
sang tdi- Khi eUdng do bUe xa tdi nho thi he so
hap thu l6n
nen bUc .xa tU dong va buc xa cam Ung sinh
ra hau nhU bi hap
thu het, hoat dong Laser eoi
Khi eUdng do
nhU bi cam.
xa tdi v6 cung Idn thi he so hap thu
bAo hoa va hien
tUdng tay
trang (
bile
trd nen nho. Luc do sU
bleaching) cua chat hap
thu xuat hien, anh sang di qua chat hap thu hau nhU khong bi
hap thu. Nang lUdng dudc tich
xung. Ly thuyet
nghien cUu [115].
chung
cac
ve
tu til trUdc bUe
hien
tUdng
dUdc Szabo va Stein
tac gi4 [36,37,42,105,117] khi nhien
euu PQS trong Laser- CO2 da
tim ra dieu kien
PQS lien quan tdi toe do tich thoat dao
khuech dai va hap
xa thanh mot
thu. Co
the xem
xuat hien xung
dong cua moi trUdng
them ve
hien tUdng nay
trong cae cong trinh gan d-ay [24^28 , 51, 77 , 99 , 115 ] r
^ .2 Hien tUdng hon loan guana
Khi nghien cUu tinh khong on dinh trong LSA, cac nha vat
ly thay xuat hien hien tUdng hon loan
quang,
hieu lina nay
dUdc Mrugala,Peplowski [96] va Antoranz,velarde[22] quan sat
dau tien. Hien
tudn^
hon
loan
trong Laser CO2 [45,73] va
da eho thay dieu
tdi ap xuat hdi bao hoa 1
tU
hien hien
dudc nghien cuu
Cac tac gia
tUdng nay
lien quan
doi vdi Laser khi ) va thdi gian
mang
dUde phun ( doi vdi Laser
da
Laser ban dan [75].
kien xuat
song cua cae phan
quang
trong
mien
phun va mien khong
ban dan ) co the tham
khao them
trong cac cong trinh [9,40,43,46,63,67,72,73,96]
1.3 Hien tUdng phan nhanh
Khi nghien
cUu he
LSA cac nha
thay rang e6 su
thay doi
d ieu. kh i'^n cae
rham
hUdng. Dembinski.
so
lien tiep
cua
mo i
thUdng (la
thu bao hoa) d eho eo the
thdi, do la
[ 47,55 j nhan
trang th.ai
^ ruen^3
cua he khi
"c ron g bi.iong cong
Mandeir47] va Srneux [55,56] da budc dau
mo ta gian do phan nhanh cua
hdn laser thong
nghien cilu
bcm nang
laser. Ta biet LSA
laser khong
co loi the
ehUa vat
lieu hap
dieu khien dUde hai tham
Ludng moi
truong khuyech
36 dong
dai va hap
thu. He phudng trinh LSA eo hai kha nang phan nhanh ke
nhau theo thdi
gian.
Hudng
phan
nhanh
khoang thdi gian khi cUdng do bien doi
thai CO eUdng
do bien
doi tuan
phan nhanh thU hai bien doi tU
doi tuan hoan
sang
trang
dau
tiep
tien itng vdi
tU "zezo" den
trang
hoan cheo thdi gian. HUdng
trang thai
eo eudng do bien
thai dUng. Cac cong trinh [23,44.
9*4] cung de cap tdi hien tUdng nay.
1.4. Hien tUdng lUdng on dinh auang hoc:
Ludng on dinh quang hoc la hien
thai anh sang on dinh khi
chi
tUdng truyen hai
c6 mot trang
t6i. Hien tUdng nay xuat hien trong cae
hap thu bao hoa
va
trong
cae
(khong ehUa moi trUdng khuyech
hap thu. Hien tUong
OB dUde
buong
thai anh
tr^ng
sang
laser ehita vat lieu
cong
hUdng thy dgng
dai) chUa day cac
Szdke [116]
nguyen tU
phat hien Ian dau
-7
tien vao nam 1969. TU do
OB trd thanh mot
Ung chinh trong hoat dong
[107,97,10] quan
eua LSA,
tarn nghien
trong* nhung hif^u
dUde nhieu nha
cUu do
nhung ilng
vat ly
dung mdi me
cua no trong cac llnh vuc.
Nghien eUu dieu kien xuat hien OB la van de kha ly thu,co
hai yeu to lien quan tdi dieu kien xuat hien OB la rtinh phi
tuyen cua moi trUdng tUdng tac vdi trUdng
dien
tU va
nang
lUdng hoi dUdng ( feed back i . khi ngtion nang lUdng hoi dudng
la hoan toan quang hoe ( all optical ) , tUc la bile xa d
trucJng phi tuyen
la do
bue xa
laser eua
moi
chinh buong cong
hUdng cung cap. Thiet bi nay dude goi la tU t^i (Intrinsic).
Khi nguon nang ludng hoi dUong la do
dat vao tinh the cung cap
mot the hieu ben ngoai
de tao thanh tinh
phi tuyen nhan
t^io, thiet bi nhu r.he goi la ngoai lai (hybrid) [ 104] .
He tu tai quang hoe dUdc tao thanh tit ba
phan tu,nguyen tu t\i do TnB],
loai vat chat :
moi truong kerr,
[94], chat
ran chat ban dan [19,20].
He ngc-^i lai quang hoc dudc Smitb va Tunnex" [114]
nghien
cUu Ian dau tien. Cae ong chieu buc xa laser He-Ne qua buong
cong hudng eo dat tinh the dien quang
KDP lam bien dieu
pham chat moi truoni^ trong buong cong huong, the
dUdc dat len tinh the de tao tinh
phi tuyen,
hieu
dcp
200v
khi quan sat
bile xa ra cae tac gia da thu dude hieu Ung OB.
Moloney [93]
da chUng
to
rang he
LSA vdi buong
hUdng dang vong co the xuat hien OB khi
het mot vong trong
buong cong
cong
thdi gian bUc xa di
hUdng Idn
hdn thdi gian tai
hdp eua he nguyen tu moi trUdng.
Muiier [97] eho rang
dinh trong cae
he LSA
dieu
vdi md
kien de xuat
rong dong
thi chat hap thu phai bao hoa nhanh hdn
hi^n lUdng
on
nhat chiem Uu the
so v6i chat khuyech
dai.
V6i laser khi
thi md
rong dong
Ngoe Ha [10], Vo DUc LUdng
cua he so tich
thoat cua
suat ngan khuyech
dai
nhat chiem
[12] neu len vai
hai moi
phai
Idn
trUdng. De
hdn
ngan
Uu the,Phan
tro quan trong
eo OB thi ap
hap
thu. Bang
s
phUdng phap he
phudng trinh
toe do,
e.ae
dUde nang lUdng can thiet d loi vao de
tac gia d^ t m h
co the nhan dude hai
gia tri ngang luong d loi ra.
Kawaguchi [75] da nhien cUu hien tudng OE trong laser ban
dan dang phun loai doi.Ong thay rang, khi thdi gian song eua
cac phan tU tai trong mien
duoc phun vao
dUde phun xap xi"' bang nhau
the xem hien tUdng
trong
thi lUdng on dinh
OB trong
laser ban
mien khong
xu^t hien. Co
dan trong
cac cong
trinh [102,81].
Nhu tren ta da biet, hieu Ung lUdng on dinh
hai loai : OB do hap thu
sang vao vat chaT: dat
va
OB do tan sac.
trong
buong
hieu ung xay ra dong "chdi ;
anh sang tdi cong hudng" mot
Khi
ehieu anh
cong " hUdng thi co hai
hap thu va tan sac. Neu tan so
each chinh xac voi
ehuven cua nguven tU thi sU tan sac
trong. Ngudc Lai neu hieu
quang hoe co
khong dong vai tro quan
so tan so
so hap thu nguyen tu Idn den
tan so dieh
eua bUe xa
tdi v,a t.an
mUe c6 the bo qua
hap thu thi
ta CO luong on dinh tan sac.
OB hap thu xuat hien khi chat hap thu
Ssoke [116] la
ng^.ldi dau
Ong tien h.anh "chi nghiem
CO2 ( vdi bUdc
tien phat
nhu sau:
song • 10, 6>im
Fabry-perot ehUa day chat khi
hien ra
tren
) co
bao
duong di cua laser
dat
tac gia
til bang ly thuyet ban co dien,
khi moi
hoa.
hieu ung nay.
buong
cong
SFs va ap suat cua
thay doi nhd he bdm chan khong,
hoa thi he so hap thu ti le
trd nen
hUdng
no eo the
mo ta trUdng dien
trudng hap thu bao
nghich vdi eUdng do bile
xa tdi
trong buong cong hUdng. Do phu thuoc vao he so hap thu nen d
trang thai diing trUdng dien tU co hai gia tri :
cong hUdng khi he so hap thu Idn,
va gia tri cong hUdng khi
he so hap thu nho. Liic do trUdng bile xa
dot ngot va hau nhU 100%
truyen qua tang len
anh sang dUdc truyen
thu. Nhu vay ta thay rang do sU phu thuoc
vao cUdng do bite xa ma dudng cong dac
cong tre. Do la lUdng
on dinh
gia tri mat
qua chat hap
cua he so hap thu
trUng loi ra la dudng
do hap thu. Co the
xem them.
SU giai thich cd che tao thanh vong tre trong cong trinh eua
- 9 Lugiato [84] OB
hap
phUdng phap ban
co
thu
dUde
dien
trinh toe do [97],
nghien
[108]
OB hap
va
eitu
ly thuyet bang
phUdng
phap he phUdng
thu trong
cac laser
khi [107],
laser mau [97], laser ban dan [751 da dUdc xet den chi tiet.
Cae nha thUe nghiem da nghien eUu hien tUdng OB
hap
thu
bang each dat chat hap thu SFs, CHsOH, CHsF trong buong cgng
hUdng dang vong [10] cua laser khi CO2.
LUdng on dinh do tan sac xuat hien do tinh phi tuyen
eua
moi trUdng. Tinh phi tuyen -he hien d eho cae dai litdng
dac
trUng eho moi trUdng nhii eh let suat phu
bile xa. Lugiaro da giai
tan sac trong moi
chat phi tuyen
hUdng. Do truyen
thuoc" vao cUdng do
thich bang ly thuyet
trudng Kerr
[84,85]. Gia
co chiet
suat no
qua
moi
eua
dudc chUa
trUdng
hien tUdng OB
sU co
mot vat
day buong cong
theo dinh nghia cua
Born va Woff [34] la ty 36 giUa cudng do anh san.e truyen qua
IT va cUdngdo anh sang -oi Iv :
0 day F
=
J := 2nnoL (^/2''
4R / T
vdi
R ^ T = 1, R
-
do
phan
la do lech pha khi anh sang di het mot chu
trinh trong buong cong hucJng, x la bUdc song bUc xa ,
ehieu dai buong cong hUdng .Khi $ = 2
thay rang de truyen
qua la
toan
phan ta
chiet suat cua moi trUdng .Khi co bile
phi tuyen thi chiet suat moi
chiet
co the thay
phu
la
*? ta
doi
xa tdi vao moi trUdng
trUdng se bien doi
suat
L
n N ( N la so nguyen )
thi sU truyen qua la toan phan (T=l) .Tii bieii thilc cua
dd bUc xa. Ta co
xa
thuoc
theo eUdng
vao eUdng do dUdi
dang :
n (I) = no + nl
(1.2),
V6i no- chiet suat ban dau
khi chua c& bile x§.
,n la h^
so phu thutpc vao tinh chat m.oi trudng, Khi eo bile xa t&i thi
•
cUcJng do anh sang trong buong eong hUdng I se tang va '5 cung
10
tang len tdi gia tri gan cong
hUdng
dattdi gia tri ngUdng I^^ - Itvi
nggt
tang chuyen
til trang
eUdng -do cao; Pha
dfit
tdi
cU6ng do anh sang tdi tdi
2TTN
.Khi anh sang
thi eUdng do
thai
eo
gia
tri
eUdng
truyen ra
do
thap
tdi
dgt
sang
cong hUdng . Khi giam
gia tri Ir.n
thi cUdng do
truyen
qua giam dot ngot tao thanh vong tre quang hoc.
Gibbs [60] la ngUdi dau tien dUa ra thiet bi OB tan sac.
Thiet bi nay gom
mot
buong
cong hUdng chiia
day
vat
chat phi tuyen la hdi
Na va
Laser mau eong suat cd
50 mw
ehieu v.ao buong
hUdng
eong
nay. Buc xa loi
nhu hinh 1.1, do
CO
dang
chiet
suat
hdi Ma phu thuoc vao cUdng do
buc xa toi
hien
cua L.aser mau
tudng ludng
xuat hien . Cac
nghien cuu
'JB "an
•n
cong
ma
llnh
t. r i n h
sac
co
the xem trong [53,55,57,60].
Hinh 1.1- Pi cong suat vao
p2 cong suat ra
Sau day ehung toi trinh bay
mot
so ket qua thUe
nghiem
hien tUdng lUdng on dinh quang hoc tan sac ma chung toi quan
sat dUde khi tien hanh thi nghiem v6i laser khi Ar .
Sd do quan sat thUe nghiem dUdc bo tri theo hinh ve (1.2)
i
Hinh 1.2 sd do quan sat thUc nghiem
Trong do : A- laser Ar
hoat dong trong che do lien tuc
vdi cong suat khoang 1 mw ,B- thau
f =6em.
C- cuvet
chUa rUdu
ki.lih hoi
pha iot
tu vdi tieu cvL
vdi nong do thap, D
- 11 - ,
- man quan sat bUc tranh giao thoa
eua chum tia ,^- thiet bi
do cong suat chum
- Kinh hien
tia buc xa,
F
vi qukn sat
sU chuyen dong cua chat mau trong cuvet.
Bile xa cua laser khi Ar
qua thau kinh se hoi ty tfi tam
cuvet mau.Do tac dung nhiet eua bUe xa ,vung chat long tai
tam cuvet se nong len.Ta co sy phan
do trong dung d^-ch:
bo
khong gian ve nhiet
nhiet dg t^i cac diem khac nhau se khac
nhau. Chiet suat eua moi trUdng thay dbi theo nhiet do,
vay n la ham phu thuoc vao v^
tri quan sat. Til [
bdi
34] ta co
the viet :
Trong do :
i,8.10-^(dq)''
^ =
at
, A T = T(r;-l, y(},' T„
la nhiet do chat long khi chua eo bUe 'xa tdi va T(r)la nhiet
do tai diem quan sat each
tam hoi tu vdi khoang
each la r.
Khi bUe xa tdi cuvet tang len t^hi do chenh lech nhiet do
cang Idn. TU '' 1.3 >
ta thay
rang chiet
giam dan va nho nhat tai tam hoi tu,
qua cuvet se khuc xa ve hai
dung nhu mot thau
kinh phan
tia bUc xa quan (sat tren
se
do vay bUc xa laser di
ky.Biic tranh
(1.3) khi cong suat loi vao P-.- eon
a)
suat moi trudng
phia. Luc n^y cuvet m.au
man D
AT
) dUde
eo tac
phan ky cua chum
ghi lai
tren hinh
nho (P=20mw - trUdng hdp
bile tranh la mot eham sang tron. Tang P-y cham sang do to
len va xuat
Tiep tuc
hien cac
tang Pv
vong tron
dong tam ftrUdng hdp
b ).
thi cac vong tron nay se xuat hien them
rlhieu ( trudng hdp c). TU (1.3) ta thay cae tia sang gan 'tam
hoi tu se khiic xa manh hdn cac tia sang d xa tam ,do d6
tia sang nay
se gap nhau
va giao thoa tao nen cac vong tron
dong tam.
• •
Khi eong suat Pv- dat t6i
bUc tranh cac vong
cac
tron dong
vao do la cac vung sang nhU
gia tri
tam dot
tdi han (P^^ =150 mw)
ngot bien
hinh ve (1.3 i .Luc nay
•loi ra dot ngot giam.Khi giam cong suat
loi vao,
mat , thay
eudng do
cUdng ao
^BB^E^ w W
idBe^B^^^BBHU«^-
•B9HBB|BHRr*'
^S^S^BSS'iit'
'•^sgBH|H||B|
s'^^HHBn
t^^^m^'-
^iMH^BH
^H^^BSj^^V
' - ^Sttfi^^B^^BSu
'^H^^B^^^BHI
^B^^Ssv ^' -
'' '^9^^^BB^B
S^S^SKS''
Hmh 13
H(nh 3nK phan ki" ctia cUlm, lia
USER.
19
loi ra •::un,^ khong trd ve gia tri ban
dau. Ta chu duc^c dudng
Gong tre tren .ninh fl.4)
(y/^^)
Hinh 1.4—Su ohu thuoe
IR ( ?—)
Ngoai ra chung toi cung khao sat sU bien doi cua eUdng do
bUc xa ra khi thay del nong do duns
cung nhu su phu thuoc thoi
gian
dich hoac do day
cua hien tudng
!!:uvet.
lucng
on
dinh quang hoc tan sac.Co the xem chi tiet trong ohu luc (5)
Tren day la mot sd eong trinh
nghien
eUu heat dong cua
LSA. Cae tae gi.a da dua ra dieu kien ton tai,
van de lien quan
tdi cac
hifu ilng
hoat dong cua LSA . trong LSA
cilu nhu khao sat cae van
[78,791 dac trung
phi tuyen
con nhieu
ditng [70] anh hUdng sU thang
bile xa
xay ra trong
van de
de lien quan tdi
eUdng do
ed che va cac
diem chuyen tiep
trong trang
giang pha
nhUng hUdng nghien ^Uu hien nay la khao
he LSA khi mot trong nhUng thaon so moi
phai nghien
thai khong
[71] ...
mot trong
sat sU ^hay doi cua
trUdng bien doi theo
thdi gian [54,56].
Laser chua vat lieu hap thu
bao
hoa dong vai tro
quan
trong trong ky thuat bdi nhung Ung dung mdi me cua no. TrUdc
het phai ke den sU dong gop trong phUdng phap pho laser : tao
xung cUc ngan, do nhay
tach vach hap thu. . . -hien
CO y nghia Idn trong viee
ilng dung vao
nhu tao nen cac yeu to logic va b9
tudn,^ OB
may tinh quang
nh6 quang hoe,
cae yeu
to " va " va "hoac"
Khi nghien eUu LoA vdi buong
hoe
,
cong hUdng Fabry-perot
ta
LO
khong the bo qua anh hUdng cua hieu Ung tao hoc. Day l^a mot
trong nhUng net dae trUng eua buong eong hUdng loai nay.
TrUdc khi di vao trinh bay
toi se gidi thieu
so qua
noi dung
ve vai
cua luan an
tro eua
ehung
hieu ^ing tao hoc
trong hoat dong cua LSA voi buong cong hUdng Fabry - perot.
2 .anh bUdng eua hi*fu Ung t;^o
hoe (
hdi-? burning 'gffeatl
Trong hoat dong cua laser chua vat 11*^11. hap thu bao hoa,ta
biet trong buong cong hUdng Fabery -
perot
trUdng phan
bo
khong dong nhat. Tuy theo tUng loai gUdng cong hUdng [17] ma
nang lUdng eua
trUdng tap
trung thanh
cac
tieu. Khi ta dat cac ngan khuech dai va
cong hUdng thi cUdng do
sU thay doi cua trUdng
tao hoc trong hoat
mode phat ra
fi,
hap thu trong buong
cung bien thien
chinh la anh hUdng
dong eua
cae he
ing nay the hien d eho eUdng
vi tri eua c.e.c ngan khuech
eUc dai va cUc
cua hieu Ung
LSA. Vai
:ro eua hieu
do mode phat ra phu
d.ai va hap
theo
thuoc vao
thu dat ^i-ong
buong
cong hilong [97] , mkz khac no con phu ehuoc vao *an so mode
phat [107 ] .
A.^2dke [116] da nghien eUu hoat dong cua he LSA vdi buong
cong hUdng Fabery - perot.DUa tren ly thuyet ban co dien ong
da xay dUng dUdc phuong trinh
eua vec td cudng do dien
eong hUdng nen cudng do
khac nhau. Ta eo
the mo
truyen song
-DrUdng . Song
v6i sU
di lai trong
dien trUdng tai tilng
ta trUdng
El
trong buong
@
E2
E3
El^
E2
TrUdng tai thdi diem nao do tren gUdng (1) la
E'
^2. = fE^«
E, = 5 E,
Ei
buong
gUdng la cung
theo sd do:
®
"Chay- doi
cong hUdng
V
Trong do : 7 va
la
do
phan
xa va do truyen qua eua
trUdng. o( la he so hap thu . Nghiem eua he phUdng trinh tren
chinh la gia tri
trUong
khi
cong
nguyen til moi trUdng trong buong
hUdng
vdi
dao
eong hudng. Tuy
dong
nhien tac
gia cung ehUa neu ro anh hUdng eua hieu Ung tao hoc.
Muller [97] da xet vai trd cua hieu Ung do trong laser co
md rong dong nhat la noi bat (chu yeu xet vdi laser mau ) de
mo ta hoat dong cua he LSA, tac gia
da xay
dUng he
phUdng
trinh toe do mo ta sU thay ddi theo thdi gian eua sd
photon
nghich dao do tich luy d cae ngan khuech dai va hap thu.
thay dude vai tro
ddi vi tri cua
cua
hieu
itng
tao
hoc tac gia da
dai
va
cac
ngan
khuech
laser thildng ("khong
chua
mdi
trUdng
cUdng do mode phat gan ngudng
- perot v.a buong
eong huong
khac nhau nay la
do
kha
loai buong eong
huong. Khi
chat khuech dai
d giua
hoa de hdn so vdi
cung anh hUdng
dinh sd mode dao
bao
sd di co sU
thu dat
gan gudng va
hUdng thi
kha nang bao
ngUde lai. . .
len sxi eanh tranh
dong. Hien
la 2/3
hUdng Fabry
hoa khac nhau cua tUng
chat hap
buong cong
truong hdP
thu ^ thi ty le
trong buong cong
nang
thay
hap thu .Ddi vdi
hap
loai vong
De
mode do
tUdng lUdng
Mile do
bao hoa
do no
cung xae
dn dinh
ehi xuat
hien khi chat hap thu de bao hoa hdn so vdi chat khuech dai.
Do hieu Ung tao hoc ma
dudng cong tre trong
khac nhau ( khi thay ddi vi
tri cac ngan ) se
ret. Dieu nay the hien ro tren hinh (1.5)
cae trUdng hdp
khac nhau ro
11;
Muller cung
kien xuat hien
dua
S^'pbo w-iori^xa
ra dieu
OB
ddi
vdi
tilng trUdng hdp cu the.
Khi
ca hai moi trUdng
dat
giUa
buong cong hUdng
thi
dieu
kien xuat hien OB la:
P>Pmin =1 + k/^to
Trong do P la
ty
eUdng do bao hoa
moi
ti^n^ Iv't/pt^ ^rn,
le
trudng
Hinh 1.5 a.Ca hai ngan dat
khuech dai va hap thu , K-dac
giUa buong eong hUdng
trUng eho thdi
gian song cua
b.Ca hai ngan dat gan gUdng
phoron trong buong cong hudng.
^•b dae trung eho nang lUdng bdm hap thu. Khi moi tritdng hap
thu da^ gan gUdng va moi
trudng khuyech dai ''la'
gi^'.a buong
cong hudng, dieu kien xuat hien OB la:
P > 2. 3 f 1 + k/^>^ )
Tac gia cung ket luan
dinh quan sat thay rd
rang vdi mode r^a
tam
hon,
Doi vdi laser khi vai tro eua
hieu ung
hien d chd tao thanh Lamb dip [14]
khi cae phan tU ( Phan
tU,
chuyen ddi giUa hai mue
khi
tao hoc
cac phan tit khi se tUdng
nguyen tU tU do,
con chuyen dong
tac cUc dai
man he thtic
•
-
eon the
bUc xa- Trong laser
I - on ) khi
vdi van toe
day. chang han cd song dien til vdi tan sd 9
9 =
thi lUdng dn
di
v nao
qua tap hdp
vdi cac phan
til thoa
.
^o(^-f)
U^)
f -
Trong do Po la tan sd chuyen ddi giUa hai mile
nang lUdng
( Po = ( Es -El )/h ) , c - van toe anh sang. Song diing trong
buong cong hUdng Fabry- perot vdi tan sd p bao gom hai hu&ng
1 ^
(di va ve ) . NhU vay luc do
vdi hai nhom phan tU
xay ra tUdng tac trUctng
chuyen dong
ngUdc ehieu nhau
dien til
vdi v=Ln
toe V. Khi bi^e xa thi h^m phan bd dd tich luy d cac miic tren
theo van
"hoc" . Khi ^ =>^o thi
toe co hai
nhau. Dd la hien tUdng lambdip.
laser tai ^ ~^o
se
nho
hdn
Nhu vay
so
vdi
hai hoc se trung
cong xuat phat cua
eong
:':uat
phat tai
y < >>o hoac P > 9o nhu hinh (1.6)
Saloma va Stenholm [107]
md ta hoat dong cua laser
khi '/oi chat hap
thu bao
hoa
b a n g c a c phUdng trfnh.
han
CO d i e n . s u r-tuat
hien
eua
lampdip
dUde
giai
thich trong thuyet
nhieu
loan cua eua Lisitsyn
Chebotaev [41] . Su
va
khac
X
nhau dd bao hea
trong
e.ae ngan khuech
dai
hap thu dUa den
cac
"hoc"
tao
t-ai tan
cong hildng vdi
dd
va
nen
V
'
Hinh 1.6 -3u phan bo nghich
dao dd tich luy.
sd
rong
mien nang lUdng bdm tUdng
Ung. Tren
thay
dd
sU
hinh (1.7) eho
phu thuoe eUdng
1
vao
hUdng
A
do lech
=: o-(j/ku
cong
khi
thay ddi bom hap thu va cd
Sinh bdm khuyech
Tin. hinh
dieu
ve ta thay
kien de xuat
lambdip
dai.
rang
hien
Hinh-1.7
la dao ham bac 2
1(A) vdi cac gia
tri khac nhau >ft-
cua 1(A) phai ddi dau tai
A = 0 . Tac gia da tim ra dUdc gidi han bdm hap thu de
lambdip trong md rong khong dong nhat.
Tran Thi Thu Ha
nhan
[3]
nghien cUu LSA vdi buong cong hUdng dang vong bang ly thuyet
-. 17
ban cd dien. Qu.a nghien eiiu sit phu thuoe ham bdm hap.thu vao
eu6ng do I vdi nhung gia tri d^
Tac gia thay rang
khac
vdi
lech
dudng
eong hUdng khao nhau.
dac
trung do Saloma va
Stenholm'tim ra trong trUdng hdp song dUng , d day eac dUdng
dac trung khong cat nhau
, do vay
lambdip khong
xuat hien
tren diidng dac trUng cuong dd vao do lech eong hUdng
Thi Thu Ha da ket
luan
rang
hieu
Ung
hudng den dieu kien xuat hien va mien
the tham khao them vai trd
tao
hoe khong anh
hoat dong eua
cua hieu Ung
. Tran
OB. Cd
tao hoc trong
eac
Trong nghien eUu LSA ,cac nha vat ly da su dung chu
yeu
edng trinh [31,35,48,52,92,98].
hai phudng phap : he phudng trinh toe dd va ly thuyet ban cd
dien. PhUdng phap ban cd dien dUa tren ly thuvet lamb
khdns
dua ra sU phu thuoe tudng minh cu.a cuong dd vao cao tham
mdi trUdng.Rieng
phucng
phap
he
phudns
trinh
sd
tdc do la
phudng phap rat phu hop vo
lai toan L.bH vi no cno eac ket
qua tudng minh . eho den nay van con dude sU dung phd bien
de nghien cuu ly thuyet ve LSA..
Trong cac tai lieu cong bd hau het nghien cUu ve laser eo
md rong dong nhat. Rieng laser co md rong khong dong nhat,sU
nghien cUu ehi eo the xem nhU la bUoe dau. Phan Ngoe Ha [10]
da giai quyet bai toan LSA vdi md rong khong dong nhat trong
laser vdng.
Trong ban luan an nay ehung tdi nghien cilu LSA vdi buong
edng hUdng Fabry-perot
phUdng trinh tdc
dd.
dita
Tim
khong dong nhat se gop phan
LSA.
: oi.fi.H.^s ; , 0 !
"(i :t'X
v.U//f53 j
tren
hieu
phUdng
hoat
phap
gan dung he
dong LSA vdi md rong
vao su phat trien ly
thuyet ve
13 -
ChUdng II. GAG DAG
TRUt^G CUA LSA v6l BUONG
CQNG HUdNG
FABRY - PEROT
?.1--HE PHrJONG TRINH CCl BAN
Hoat dong cua laser chUa vat lieu hap thu
buong edng hUdng Fabry-perot dUde
trinh
bao hoa
bay theo sd
trong
dd
d
hinh (2.1)
i- -5
^
i V
Kinh 2.1. od do ho^t d')na
ciia laser
chua vat li^u
hap
thu bao hoa vdi buong edng hudng Fabry-perot.
Trong so do gom hai gUdng cong
hai ngan. Ngan A oh(\a. chat
hudng,
co tinh
giUa hai gUdng la
khuech
ngan B ehita vat lieu hap
thu bao hoa.
trong buong cong hUdng,
song anh
d^i anh sang va
Khi co bUc
.xa laser
sang se di lai
giUa hai
gUdng c^ng hUdng. Qua ngan A thi bue xa dude khuech dai len,
va qua ngan 3 biie xa se giam
day cd the la bile
dong cua laser
:
ehUa vat
di do hap thu. Buc
mode hoac
lieu hap
da mode
thu bao
xa laser d
de md ta hoat
hoa trong buong
e^ng hUdng Fabry - perot, ta sit dung phUdng phap gan diing he
phUdng trinh tdc do. Vdi phUdng
phap nay
dung dUde he phUdng trinh dae trUng eudng
khi, ciing nhU hieu dg tich luy d cac
chung toi
se xay
dg mode cua laser
ngan khuech dai va hap
thu.
Sd pho ton va he so
mode thil .j la nj va
mat mat
trong budng
cong hUdng cua
. He sd mat mat cua tUng mode phv thuoc
vao sU tan sac tren eac gUdng va tinh chat cua tiing gUdng cy
i.tt
the.
-
Trong md rong vach nguyen tit,
lien ket vdi eac
nhom
nguyen
nhat r nhUng khac nhau tan sd
til
moi mode
ed
vdi tan sd i^^j
cung do md rong dong
d tam ^^.
He sd
tich thoat d
mile tren trong cae ngan khuech dai va hap thu la
^a va iSt>.
Cac he sd nay lien he vdi nhau bdi bleu thue :
0 day
5
^^ ^^ ^^ lien he dg
che dan den sit
thay ddi
bao hoa,
tich thoat
d hai
dac trUng eho cd
ngan. NhU ta da
biet trong Laser khi,do tich thoat lien quan toi ap suat cua
tUng ngan, do vay he sd
bieu hien
do chenh lech ap suat
giUa hai ngan. Neu ap rcuat
ngan khuech dai Idn hdn
ap suat
ngan hap' thu thi ngan khuech dai eo dd bao hoa Idn hon,
dd
0< ^ <^
- Khi % >1 ta co trUong hdp ngUdc
tae gia [97]
trUdng
3di
bao hoa khi mdi
xet chu
yeu tritdng
do
luy d cac ngan khuech dai N^A^L va ngan hap thu N^-b theo
cae phrldng trinh sau:
- [ H^%in^i-nm.z,/L)Az
^N/co,
hop
Theo phUdng phap he phUdng tinh tdc dd [10,97] ta eo
the md ta sU thay ddi theo thdi gian sd photon nj , hieu
tich
ra
hap thu de bao hoa hdn so vdi mdi trudng khuech dai.
vay trong bai toan nay ta ehi
0< ^<1.
lai. Theo cae
thi hien tUdng liidng dn dinh quang hoe :
ro nhat vdi cac laser chua vat lieu hap thu
khi
^
5^
_ N
/RV
r-^i^^'n-^fTTm^-x/L)
'•»o
_
0 day, 3 la he sd Enstein, mo ta xac :
bile giUa cac mile nang lUdng.
^
Sd hang:
md ta do md rong dong nhat eua cac nhdm nguyen tU cd tan
tam iJ^ .Ta biet
trong
laser
chiem Uu the nen 7. trons
khi
md rong
sd
khdng dong nhat
(2.1) noi len sit dong
sop eua tat
-
/*
ca cae nhom nguyen tU cd cung
dd md rong dong nhat
r nhUng
khac nhau tan sd tam '^^ .
Gia thiet mdi truong buong edng
hUdng gom
tit vdi hai mUc nang ludng thi hieu dd
nhUng nguyen
tich luy giua hai mite
la:
N^ -3. = N>* =2 -Ni. 3.1
G day chi
sd 1
va 2
chi mite
nang lUdng hoat dong eua
laer ky hieu a v,^ b •::•= chi ngan khuech dai A va ngan hap thu
B. Ro a. va R w'o
dac trUng eho
mdi trudng khuech
dai va
cac ngan khuech dai va
tdc
dd bdm nang ludng trong
hap thu
. Ham nang
lUdng bdm eho
hap thu eo
the la nhu
nhau doi vdi
tat ca eac mode
va cung
ed the
mode. Chang han
vdi ngan
la khdng
khuech dai
deu doi
ham bdm
vdi eac
phan bo theo
dang Lorentz :
^/u>^
=
i^Ro
s'-^ 4 K - - S I J
Trong dd Ro la nang lUdng bdm tai mode tam i^o va Z la do
md rong khong dong nhat. Ta thay nang
lUdng bdm tap trung d
mode tam va giam dan ra cac mode ben eanh. So hang
1
trong
tong (nj + 1 ) d (2.1) dac trung eho bUc xa tU dong dong vai
tro nho be trong eUdng dd
bite xa laser,
Tuy nhien no
dong
vai trd quan trong trong viec phat bile xa ban dau.
So hang
sin ( nmjs/L ) trong
eho SU phu thuoc eUdng do mode
(2.2)
vk
(2.3)
thu .j vao vi tri
dac trUng
khdng gian
theo true z (true eua buong eong hUdng ) , 1 , L la ehieu dai
•
eua cae nean va budng edng
hUdng ,m.i la so
nguyen thoa man
21
dieu kien cong huen-g 'Cua mode thU .j .
•
mj Xj = 2L
Vdi Xj la bude song eua mode thu .j
So vdi cac luan
an
trUdc
[2,3]
trong
(2.1,2.2,2.3) eo xuat hien them sd hang
vay SU thay doi
so
thuoc vao nang
photon
lucng bom
cua
sin (
mode
ma con
he phUdng trinh
thu
phu thuoc
TT^JZ/L
). NhU
.j khdng ehi phu
vao vi tri cua
ngan khuech •rial va hap thu trong buong edng hUdng. Day la sU
khac biet giua
budng
edng
hUdng
dang
vdng va buong eong
hUdng Fabry - perot.
Tit he phuong trinh ed ban ta thay sd photon mode thu j la
nj dUde sinh ra khi di qua mdi truong
khuech dai va bi giam
di do mat mat trong buong cong hUdng cung nhu bi hap thu khi
qua mdi ".ritdng hap thu bao hoa.
Tons Z tr^-^ns f 2.2 ' va (2.3)
cae mode "rona: bue r-ca laser
chi sit dons gop eua
tat ca
:.
Trons bai toan nay eac mode d day la mode doc.
Chung r,oi
se
2.2,2.3; ve dang
chuyen
he
khac nhau
phuong
trinh
thuan tien
Khai trien ham dac trUng eho sU phu
co
ban
( 2.1,
eho viec tinh toan.
thuoc eitdng do mode vao
vi tri cua eac ngan trong budng edng huong.
sin ! rtmj2/L ) = —
L 1 - cos (2TTm,i2:/L * 1
Ta nhan thay rang hieu do tich luy
M^a la ham
bien thien
nhanh so
mdi trudng khuech dai
vdi ham cos ( 2TTmjz/L )nen
ta CO the bien doi :
TUdng tu nhu vay vdi hieu dg tleh luy moi trUdng hap thu:
^,-l
h-^ L
r I
H3U