Chng 4CC HIU NG QUANG HC PHI TUYN BC CAO

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Ni dung

So snh quang tuyn tnh v quang phi tuyn

phn cc t l tuyn tnh vi vector cng in trng phn cc khng t l tuyn tnh vi vector cng in trng

phn cc phi tuyn P c vit li l:t:Qu trnh quang tuyn tnhQu trnh quang phi tuyn bc IIQu trnh quang phi tuyn bc III

Trong chng ny, ta s xt cc hiu ng phi tuyn bc III nn s dng phn cc phi tuyn bc III.

Xt ba sng phng n sc i vo mi trng phi tuyn bc III, c hai cch biu din cc sng ny:

Cch ICch IIS dng cch I trong qu trnh tnh ton trn lpSinh vin t lm nh

Mi tng tc phi tuyn ng vi mt tn s nht nh, n gin, chng ta b phn ph thuc vo k.

Cch I

Tnh phn cc phi tuyn bc ba:

Trong : E=E1+E2+E3

phn cc ca qu trnh pht sng hi bc ba ng vi 1= 2= 3 l:

Phn chng minh trong file word Su_tron_4_song_va_su_phat_song_hai_bac_III.doc hoc Su_tron_4_song_va_su_phat_song_hai_bac_III.pdf

Sinh vin t tm phn cc khi in trng u vo biu din theo cch 2.

Bi ton: Xt s tng tc gia nh sng n sc v mi trng tinh th. Gi s tinh th c chiu di L. Sng u vo ny c dng: Dng phng trnh sng trong mi trng phi tuyn tm sng Eout thot ra khi tinh th. Bit sng ny c tn s 3, s sng k3

Bi ton: Xt s tng tc gia nh sng n sc v mi trng tinh th. Gi s tinh th c chiu di L. Sng u vo ny c dng: Dng phng trnh sng trong phng trnh phi tuyn tm sng Eout thot ra khi tinh th. Bit sng ny c tn s 3.

Hng gii: Dng phng trnh sng

1.Vit li phng trnh sng trn cho Eout .2.Gi nh Eout c dng no :3.i lng cn tm l bin ca sng E(3)4. tnh hai s hng bn v tri, chng ta ch cn ly o hm.5. tnh phn cc, dng cng thc

Cui cng chng ta tm c:Trong

Vn quan trng nht: Hiu sut pht sng hi bc ba=kh nng chuyn nh sng tn s sang nh sng tn s 3

Hiu sut=cng nh sng u ra/cng nh sng u voCng nh sng t l vi bnh phng cng in trngCui cng ta tnh c hiu sut:

Hiu sut ln nht khi k = 0 H thc (1) khng th tha mn do mi trng tn sc.(1)Tuy nhin (1) c th c tha mn trong mi trng kh bng cch trn hai cht kh vi nhau.

Mi quan h gia cc i lng sng: k: ln ca vector sng (rad/m): tn s (Hz) (mt s sch k hiu l f).

: tn s gc (rad/s)0: bc sng trong chn khng (m)n:chit sutCh : khi truyn trong mi trng c chit sut n, bc sng ca nh sng thay i nhng tn s nh sng khng thay i, mu sc nh sng do tn s quyt nh.

Gi s kh A tn sc thng:

v kh B tn sc m:

theo t l thch hpGi np v nn l chit sut ca kh tn sc dng v m

fp v fn l nng ring phn ca chng

c n()=n(3 ) =>

Trong quang tuyn tnh, chm sng song song khi truyn qua mi trng s b phn k (m rng ra) do nhiu x. khong cch c trng Rd chm bt u nhiu x- di nhiu x: Rd = ka2/2; (1) vi a l bn knh ca chm.Gc phn k d = 1,22/2ano (2)(1) v (2) khng phu thuc vo cng ca chm bc x.Kt qu trn khng cn ng khi chiu chm laser cng sut ln vo cht lng, mt s tinh th rn.

Nguyn nhn: ta c P = E + E2 + E3 + Vect cm ng in D= orE = oE + P in thm tng i r = 1 + P/ oE Chit sut n2 = r Do khi chiu nh sng c E ln vo mi trng phi tuyn bc ba, ta c n2 = r = 1 + /o + (3/4o)Eo2 i vi chm Gauss, Eo tng dn t bin vo vng trc nn n cng tng dn t bin vo vng trc chm tia b hi t vo vng trc: S t t tiu

Nu cng sut chm tia t gi tr ngng:

Pc = ncoao2Eo2/2 = co2/8n2 th s hi t cn bng vi s nhiu x: chm tia gi nguyn song song khi truyn: s t by. Nu P > Pc chm tia t hi t.Khong cch hi t i vi chm Gauss zf = zo(P/Pc - 1)-1/2 Cc qu trnh phi tuyn khc cn tr s hi t n bn knh w = 0.Ch : Cng sut ca chm u vo phi t ti ngng Pc th hiu ng mi xy ra. Cho d cng I cao nhng cng sut cha t ti Pc hiu ng cng khng xy ra.

Chit sut phi tuyny l nh ngha cng sut P=I.S

TPA l qu trnh hai photon c hp th ng thi kch thch h vt liu, l qu trnh phi tuyn bc cao hn; tit din hiu dng nh hn nhiu bc so vi hp th mt photon. Tuy nhin vn quan st c nh cc laser.S dch chuyn mt photon v hai photon tun theo cc qui tc chn lc khc nhau nn thng c dng b sung cho nhau trong quang ph hc.Xc sut dch chuyn ca qu trnh hai photon c Gppert-Mayer a ra ln u tin bng cch dng l thuyt nhiu lon bc hai. Ngoi ra c th dng phng trnh sng lin kt tnh.

Cng nh sng hp th t l vi: P = E(dP/dt). (i)Trong quang tuyn tnh, P = E Ta tnh c cng nh sng hp th P ~ E2 (hp th 1 photon).Trong quang phi tuyn, P = E + E2 + E3 + , i vi mi trng phi tuyn bc ba: P = E + E3 , khi thay vo (i) ta tnh c P ~ E4 (hp th hai photon, phn chng minh trong gio trnh, trang 91 n 94, trong chng ta gii bi ton tm xc sut dch chuyn t trng thi m vo trng thi k thng qua trng thi n ).

Hin tng TPA c quan st ln u tin tinh th CaF2 : Eu.Chiu chm laser Ruby ( = 6943 ) vo tinh th, ion Eu+2 hp th hai photon, chuyn ln trng thi kich thch, sau dch chuyn khng bc x v mc NL thp hn ri bc x phn NL cn li di dng s mu xanh lam ( = 4250 ). Lu : khc vi SHG, THG, c th xem nh 3WM.

ng dng ca TPA TPA l cng c hu ch n/c s kch thch v p/c exciton trong bn dn (o dc ng cong tn sc ca p/c exciton, trong khi O-PA ch quan st c p/c exciton trong resttrahling band).TPA c dng to ra s kt ng b cc ht ti trong khi vt cht.TPA cn c dng d cc tt ca exciton khi khng th d bng O-PA.

Ch Tn s c th cng nhng bc sng khng th cng. Vd: trong to tn s tng 1+ 2= 3 nhng khng c vit 1+ 2= 3