Co So Dong Hoc Laser

7/30/2019 Co So Dong Hoc Laser

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Khoa KHOA HC VT LIU

VT L LASERGing vin: TS. Phan Bch Thng


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achbnti:http://mientayvn.com/Cao%20hoc%20quang%20dien%20tu/Semina%20tren%20lop/seminNi bn c th tho lun:http://myyagy.com/mientay/

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D n dch hc liu m:http://mientayvn.com/OCW/MIT/Co.html

Lin h vi ngi qun l trang web:Yahoo: [email protected]

Gmail: [email protected]
mailto:[email protected]:[email protected]


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Khoa KHOA HC VT LIUVT L LASER

CHNG TRNH MN HC VT L LASER

Chng 1: C s ng hc ca laser

Chng 2: L thuyt v h cng hng quang hc

Chng 3: S lan truyn ca chm laser

Chng 4: Cc phng php to mi trng mt o ln trong my phtquang lng t

Chng 5: Cc tnh cht ca chm laser

Chng 6: Cc loi laser

Chng 7: ng dng ca bc x laser


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CHNG TRNH MN HC VT L LASER

Ti liu tham kho

1. Vt l cht rn, L Khc Bnh v Nguyn Nht Khanh, Nh xut bn i hc Quc gia Tp. HCh Minh, 2002.

2. Quang ph nguyn t v ng dng, Nguyn Vn n, Nh xut bn i hc Quc gia Tp.H Ch Minh, 2002.

3. C s k thut Laser, Trn c Hn v Nguyn Minh Hin, Nh xut bn gio dc,2001.

4. Nhng ng dng mi nht ca Laser, Ngy Hu Tm, Nh xut bn Khoa hc v K

thut, 2003.5. Vt l Laser, Trn Tun v Nguyn Hu Ch, Nh xut bn i hc Quc gia Tp. H

Ch Minh, 2002.

6. Laser Physics, L. V. Tarasov, MIR Publishers, 1983.

7. Principles of Lasers, Orazio Svelto and David C. Hanna, Plenum Press.


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Chng 1: C s ng hc ca Laser

1. Tng quan v c s vt l ca laser

2. Cu to ca mt my pht laser

3. iu kin lm vic ca my pht laser

4. Ngng pht

5. Ch lm vic ca laser

6. Ngng bm

7. iu kin t kch


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1. TNG QUAN v C S VT L CA LASER


Khuch i nh sng bng bc x cng bc


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Lch s pht trin ca nh sng laser



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Theo l thuyt lng t, cc nguyn t ch tn ti nhng trng thi nng lng gin on.

Trng thi ng vi nng lng cc tiu gi l trng thi n nh hay trng thi c bn.

Trng thi ng vi nng lng ln hn trng thi c bn gi l trng thi kch thch.

Trong iu kin bnh thng, nguyn t trng thi bnh thng v tun theo phn b Boltzmann.

Nu mt s trng thi kch thch c cng mt gi tr nng lng nhng trng thi suy bin.

S trng thi ng vi cng mt mc nng lng gi l suy bin hay cn gi l trng lng

thng k ca mc, ki hiu l g.

Di tc dng ca bn ngoi, cc nguyn t s dch chuyn gia cc trng thi. Vi mi dch

chuyn nguyn t s hp th hay bc x mt lng t nng lng v tun theo nh lut bo tan

nng lng. Tn s ca lng t bc x hoc hp th l

EEE ki


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C s l thuyt ca Laser chnh l tin ca Einstein (1917): khi c tng tc gia nh sngvi cc nguyn t:

1. Qa trnh hp th mt lng t nh sng

2. Bc x t pht

3. Bc x cng bc

Chiu vo nguyn t mt chm bc x c mt nng lng (). Xt qu trnh hp th v bcx nh sng trong mt nguyn t vi hai trng thi c nng lng E 1 v E2 (E2 > E1).


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E1

E2

Trng thi cui

E1

E2

E1

E2

Trng thi u

Sau khi hp th photon, nguyn t chuyn ln trng thi kch thch E 2 > E1.

1. Qa trnh hp th


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E1

E2

Trng thi cui

E1

E2

E1

E2

Trng thi u

Nguyn t b kch thch c th chuyn v trng thi c nnglng thp hn mt cch t pht bng cc pht ra photon c cng

tn s vi photon kch thch.Cc chuyn di t pht l ngu nhin nn bc x t phtkhng c tnh kt hp (photon pht ra truyn theo phng ty v pha ty ).

2. Qa trnh bc x t pht


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E1

E2

Trng thi cui

E1

E2

Nguyn t trng thi kch thch, di tc dng ca trngbc x (photon kch thch) c th chuyn tr v trng thi c

trng thi c nng lng thp s photon bc x s ln hn sphoton kch thchnh sng c khuch i.

Trong bc x cng bc, photon pht ra c cng tn s, cngphng truyn v cng pha vi photon kch thch.

3. Qa trnh bc x cng bc

E1

E2

Trng thi u


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nh lng qu trnh dch chuyn

khi nim vn tc ca qu trnh. Albert Einstein xc nhh s ca tng qu trnh v ch ra rng tc ca cc qu trnh ny c lin quan vi nhau.

1. Qa trnh hp th

Tc ca qu trnh hp th t l thun vi s nguyn t N1 trng thi c nng lng thp E1v mt nng lng () ca bc x ti cc nguyn t

11212

NBdt

dN

B12l h s Einstein i vi qu trnh hp th, c th nguyn cm3.J-1.s-2.

Mt nng lng () hay mt ph khi ca bc x tn s dch chuyn (l phn nnglng cha trong mt n v th tch ca chm bc x trong mt n v qung ph) c th nguyn

l J.cm-3.Hz-1 hay J. cm3.s.

Nu mt photon cng ln th s hat ng hp th cng ln.


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2. Qa trnh bc x t pht

Tc ca qu trnh bc x t pht khng ph thuc vo mt nng lng ca bc x m ch t l thun vis nguyn t N2 trng thi kch thch.

212

21 NAdt

dN

A21l h s Einstein i vi qu trnh bc x t pht, c th nguyn s-1.


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3. Qa trnh bc x cng bc

Tc ca qu trnh bc x cng bc t l thun vi mt nng lng ca bc x v s nguyn t N2trng thi kch thch.

221

21 NBdt

dN

B21l h s Einstein i vi qu trnh bc x cng bc.

Nu mt photon kch thch cng ln th s photon bc x ra cng nhiu.


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Trong trng thi cn bng nhit, s cc chuyn di iln phi bng s cc chuyn di i xung

21

2

112

21

221221112

BN

NB

A

NBNANB

Theo nh lut phn b Boltzmann

21212112

212

112

21

2

1

2

1

2

1

,,

21

ggAABBB

T

Beg

gB

A

eg

ge

g

g

N

N

Tk

h

Tk

h

Tk

EE

B

BB

1

1

Tk

h

Be

B

A

Theo nh lut Planck

3

3

3

38

1

18

c

h

B

A

e

c

h

Tk

h

B

T s xc sut ca qu trnh bc x t pht vcng bc l

1 Tk

h

BeB

A

h


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rng v ng bao ca vch ph

Cc mc nng lng ca nguyn t c rng nht nh ngay khi khng c tc ng bn ngai. rng ca

mc nng lng c xc nh bng nguyn l bt nh Heisneberg v ph thuc vo thi gian sng ca nguyn

t trng thi . hE kk .

Thi gian sng ca trng thi c xc nh bng tng xc sut ca nhng dch chuyn t pht xung trng

thi thp i, tc l xc xut ngho ha ca mc k.

ik

ik

k

k hh

E

rng ca mc nng lng cng ln nu tui th ca trng thi cng nh.

Mc siu bn c rng nh. Trng thi c bn c tui th ln nn c rng rt nh.

Cc mc kch thch c rng kh ln.

Do c s nhe ha mc nng lng, ngay khi khng b kch thch, nhng vch ph bc x hay hp th ca

nguyn t cng c rng nht nh.


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rng xc nh v tn s gia hai mc nng lng b nhe ha c xc nh bi rng ca cc mc nnglng

kiki EE

1

rng vch ph ca nguyn t ring r v khng b kch thch gi l rng t nhin ca vch ph.

ik

Ek

Ei

kiik EE

1


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Da vo th nng lng ca h c th xc nh nh tnh c cng v rng ca vch ph.

Mc 1 ng vi trng thi c bn nn c E1 = 0. Gis xc sut dch chuyn 21 rt lntui th mc 2

nh

rng E2ln. Mc 3 c rng E3nh hn. Ph ca s 3 mc gm 3 vch vi tn s 32, 21, v 31.

Vch 2-1 c cng ln nht v xc sut dch chuyn ln. Vch 2-1 kh rng v ngho ha ca mc 2 ln.

Cng 2 vch 3-2 v 3-1 nh v xc sut dch chuyn nh nhng khc nhau v rng. ngho ha canhng mc 2 v 3 ln hn nhiu so vi mc 3 v 1.

1

2

3

32 3121

J()


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2. CU TO CA MT MY PHT LASER

Lasermy pht lng t cng quang hc gm 03 b phn chnh:

1. Mi trng hot cht

2. Bung cng hng

3. B phn kch thch



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Khoa KHOA HC VT LIU


1. Mi trng hot chtL mi trng vt cht c kh nng khuch i nh sng i qua n.

a. Hot cht l cht kh Laser kh Kh n nguyn t: ArI, XeI, NeI. Ion kh n nguyn t: ArII, KrII.. Kh phn t: CO

2, CO, N

2..

Hn hp kh n nguyn t: He Ne Hn hp kh phn t: CO2N2He, CON2H2O

b. Hot cht l cht rnLaser rn Tinh th hay thy tinh c pha trn thm cc ion nguyn t him: Eu3+, Cr3+. Laser ruby: Cr3+pha tp vo

tinh th Al2O3.

c. Hot cht l bn dnLaser bn dn: GaAs, PbS, PbTe

d. Hot cht l cht lngLaser lng Pereridin Eu (BA)4ha tan trong dung mi ru ethol + methol v pha tp thm ion nguyn t him Eu3+, Nd3+..


VT L LASER


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Khoa KHOA HC VT LIU


2. Bung cng hng Gm 02 gng phn x. Mt gng c h s phn x rt cao v gng cn li c h s phn x thp hn tia

laser thot ra ngoi.

Mt trong cc gng c th c thay bng lng knh hay cch t.

Vai tr ca bung cng hng l lm cho bc x do mi trng hat cht pht ra c th truyn qua mi trnghat cht nhiu ln bc x ny c khuch i nhiu ln.

3. B phn kch thch hay bm

Cung cp nng lng to s nghch o tch ly trong hai mc nng lng no ca mi

trng hat cht v duy tr s hat ng ca laser.

Kch thch bng nh sng bm quang hc.

Kch thch bng va chm in t: nng lng in t c gia tc trong in trng c truyn cho cc nguynt trong mi trng hat cht thng qua qu trnh va chm.


VT L LASER


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Khoa KHOA HC VT LIU

3. IU KIN LM VIC CA MY PHT LASER

Khi dng bm quang hc, nh sng bm tng tc vi cc h nguyn

t ca mi trng hat cht chuyn chng ln trng thi kch thch.

Xt qu trnh hp th v bc x xy ra ti lp mng dx ca mitrng hat cht. S bin thin cng sut nh sng ti lp dx ca mitrng vi tit din ly lm n v:


VT L LASER

gB

gB

dxhNI

dxhNI

IIdP

1212

2121

12121

'

21212

'

N1, N2l tch ly ca cc h nguyn t mc 1 v 2. 12, 21l xc xut hp th v bc x cng bc.

g () l hm chun ha c trng cho s m rng vch

ph bc x hay hp th.

x = 0 dx x = l

122112

121212

, gg

dxghBNBNdP

VghBNBNP 121212

Bin thin cng sut trong ton th tch V

bin thin cng sut l dng ~ nh sng i qua mi trng hot cht c khuch i ln cn iu kin

121212121212 0 BNBNBNBN iu kin nghch o tch ly


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Khoa KHOA HC VT LIU

3. IU KIN LM VIC CA MY PHT LASER

Biu thc cng sut that khi bung cng hng Plkhi gi thit cng sut vo l P0. nh sng i qua mi

trng dx l P:


VT L LASER

cP

Kvl h s hp th ca mi trng hat cht.

vgc

hBNBNk

dxkc

dxghBNBN

P

dP

212121

121212

lkl ePP

0

nh sng khuch i Pl > P0cn kv < 0.

iu kin nghch o tch ly nhit mi trng hat cht m. Trong cn bng nhit ng, tch lyca 2 mc tun theo phn b Boltzmann

012

1

212

1

2

1

2

2112

TNN

eg

gNNe

g

g

N

N Tkh

Tk

EE

BB


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Khoa KHOA HC VT LIU

4. NGNG PHT

iu kin c nghch o tch ly cha m bo c tia laser thot khi bng cng hng do bc x t hat

cht tuy c khuch i nhng cn chu cc mt mt trong bung cng hng. Cc mt mt: nhiu x cc khu ca gng, phn x hay tn x.

Gi W l nng lng d tr c trong bung cng hngcng sut mt mt trong bung


VT L LASER

c l thi gian tt bc x

Q l h s phm cht ca bung cng hng l i lng nghch o vi s mt mt.

iu kin c s pht tia laser

Du bng = trong iu kin trn gi l ngng pht ca laser.

Q

WW

dt

dWP

c

'

gQBBBNNVW

Q

WVghBNBNPP

2121

1212

121212'

1


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Khoa KHOA HC VT LIU

4. NGNG PHT

Dng mi lin h th nht ca cc h s Einstein


VT L LASER

iu kin ngng pht ph thuc vo phm chtca bung cng hng Q, s m rng vch ph g() vh s Einstein B21.

Mt mt cng ln, Q cng nh th ngng pht cngln xy dng bung cng hng c mt mt nh.

Chn 2 mc nng lng c h s Einstein ln s lmgim ngng pht.

M rng vch ph dng Lorentz m rng ng nht

gQBNNgg

gQBg

gNN

211212

211

212

1

1

220

21

g

rng vch ph, 0tn s ti tm vch khi khng c

m rng. Trong gn ng lng cc in:

02

212

2

1

212

22

221

2

21

4

3

3

2

re

g

g

gNN

g

reB

c

er21yu t ma trn ca lng cc in.

M rng vch ph dng Doppler m rng khngng nht

0

21

221

2

2

1

2

12

221021

2ln4

3

2lnexp2ln1

D

c

DD

re

g

g

gNN

g

Trong 2 dng m rng vch ph trn, iu kin nghch

o tch ly u t l thun vi rng vch vic

lm gim rng l cn thit cho hat ng ca my

pht laser.


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Khoa KHOA HC VT LIU

5. CH LM VIC CA LASER

1. H nguyn t lm vic vi hai mc nng lng


VT L LASER

E1, N1

E2, N2

Khi khng c tc ng bn ngoi: N1 > N2

Khi c bm quang hc: N1gim, N2tng

Khi 01

2

12

kg

g

NN

H s hp th k = 0 nn h nguyn t khng th hp th nh sng c na d qu trnh bm vn tip tc

khng th chuyn thm nguyn t t mc 1 2

khng c nghch o tch ly

khng th to nh sng laser.


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Khoa KHOA HC VT LIU


2. H nguyn t lm vic vi ba mc nng lng


VT L LASER

tn s nh sng bm khng qu n sc chn mc 3 c rng tng i ln.

Mc 2 l mc siu bn.

Khi c bm quang hc: dch chuyn 1 3.

Nguyn t khng lu mc 3 nn 32 (khng bc x) v xc sut khng bc x 32

ln (32

>> 31

).

To c s nghch o mt tch ly 2 mc 2 v 1.

Do mc 2 v 3 rt gn nhau nn bc x t pht 31 rt gn bc x laser 21nhiu lon bc x laser.

E1, N1

E2, N2

E3, N3


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Khoa KHOA HC VT LIU


3. H nguyn t lm vic vi bn mc nng lng

VT L LASER

tn s nh sng bm khng qu n sc chn mc 4 c rng tng i ln.

Mc 3 l mc siu bn.

Khi c bm quang hc: dch chuyn 1 4.

Nguyn t khng lu mc 4 nn 43 (khng bc x).

Mc 2 gn mc 1 v c lin kt quang vi mc 4 bc x t pht 42 s qua qu trnh tch thot m chuynngay xung mc 1.(32 >> 31).

To c s nghch o mt tch ly 2 mc 3 v 2.

Bc x laser 32 khng b nh hng bi bc x t pht 42.

E1, N1

E3, N3

E4, N4

E2, N2

iu kin lm vic ca laser 4 mc:

43 >> 32 v 42

21 >> 42 v 12

32 ~ 0

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Co So Dong Hoc Laser