Lazery i ih primenenie
M. F. Sem (Rostovskii gosudarstvennyi universitet, Rostov-na-Donu)Opublikovano v Sorosovskom obrazovatel'nom zhurnale, N 6, 1996 g. Soderzhanie
Princip raboty i ustroistvo lazera
Kak uzhe otmechalos', generaciya v lazere dostigaetsya za schet inducirovannogo izlucheniya na nekotorom perehode mezhdu urovnyami kvantovoi sistemy. Risunok 1 demonstriruet vozmozhnye perehody v prosteishei dvuhurovnevoi sisteme, kak vyzvannye polem (pogloshenie i inducirovannoe izluchenie), tak i ne zavisyashie ot nego (spontannoe izluchenie i bezizluchatel'naya relaksaciya).![]() |
Ris. 1. Vozmozhnye perehody v dvuhurovnevoi sisteme. Veroyatnosti: Wc - spontannogo izlucheniya, R - bezizluchatel'noi relaksacii, W12 - poglosheniya, W21 - inducirovannogo izlucheniya. n2 i n1 - plotnosti naselennostei, ![]() ![]() |
![$\tau_2$](https://images.astronet.ru/pubd/2002/04/10/0001175822/tex/formula0.gif)
![$\tau_1$](https://images.astronet.ru/pubd/2002/04/10/0001175822/tex/formula1.gif)
![$W_{12} = B_{21} \rho S(\nu), W_{21} = B_{12} \rho S(\nu)$](https://images.astronet.ru/pubd/2002/04/10/0001175822/tex/formula2.gif)
i zavisyat kak ot svoistv kvantovoi sistemy (cherez koefficienty Einshteina B21 i B12), tak i ot prilozhennogo polya - ob'emnoi plotnosti ego energii
![$\rho$](https://images.astronet.ru/pubd/2002/04/10/0001175822/tex/formula3.gif)
![$\nu$](https://images.astronet.ru/pubd/2002/04/10/0001175822/tex/formula4.gif)
![$\nu_0$](https://images.astronet.ru/pubd/2002/04/10/0001175822/tex/formula5.gif)
![$S(\nu)$](https://images.astronet.ru/pubd/2002/04/10/0001175822/tex/formula6.gif)
![$n_2 = n_1e^{-\frac{E_2 - E_1}{kT}},$](https://images.astronet.ru/pubd/2002/04/10/0001175822/tex/formula7.gif)
i na verhnem urovne chastic men'she, chem na nizhnem. Poetomu dlya polucheniya inversii sredu nuzhno uvesti ot sostoyaniya ravnovesiya. Inversiya naselennostei v lazerah dostigaetsya v rezul'tate sovmestnogo deistviya processov zaseleniya (nakachki) sootvetstvuyushih urovnei i ih dezaktivacii (ochistki). Soglasno risunku 1, dlya dostizheniya stacionarnoi inversii neobhodimo vypolnenie sootnosheniya
![$F_2\tau_2 > F_1\tau_1,$](https://images.astronet.ru/pubd/2002/04/10/0001175822/tex/formula8.gif)
to est' proizvedenie skorosti nakachki na vremya relaksacii dlya verhnego urovnya dolzhno byt' bol'she, chem dlya nizhnego. Iz etogo sleduet, chto predpochtitel'noi yavlyaetsya selektivnaya nakachka i chto inversiya mozhet byt' dostignuta ne tol'ko za schet preimushestvennogo zaseleniya verhnego lazernogo urovnya, no i za schet vysokoi skorosti ochistki nizhnego. Zaselenie urovnei v lazerah mozhet osushestvlyat'sya [Karlov N.V., 1988, Tarasov L.V., 1981]: - za schet poglosheniya sveta (opticheskaya nakachka). Podbiraya istochnik sveta s sootvetstvuyushim spektrom, mozhno obespechit' vysokuyu selektivnost' nakachki. Naibolee uspeshno etot vid nakachki ispol'zuetsya v tverdotel'nyh (na kristallah i steklah) lazerah i v lazerah na krasitelyah. - v neuprugih stolknoveniyah atomov i molekul so svobodnymi elektronami, pri kotoryh chast' energii elektrona idet na vozbuzhdenie atoma ili molekuly. Svobodnye elektrony mogut sozdavat'sya ili v gazovom razryade, ili vvodit'sya v gaz v vide puchka, sformirovannogo v uskoritele. - za schet neuprugih stolknovenii atomov rabochego veshestva s vozbuzhdennymi atomami ili ionami vspomogatel'nogo gaza s peredachei energii vozbuzhdeniya ot nih rabochemu veshestvu. V nekotoryh tipah stolknovenii peredacha energii nosit rezonansnyi harakter i dostigaetsya vysokaya stepen' selektivnosti zaseleniya urovnei. - v processe special'no podobrannyh himicheskih reakcii (himicheskaya nakachka); pri etom vozbuzhdayutsya kolebatel'nye urovni molekul, prichem vozbuzhdenie mozhet byt' selektivnym. - za schet nagreva (teplovaya nakachka). Etot metod ispol'zuetsya dlya nakachki kolebatel'nyh urovnei v molekulah, inversiya na perehodah mezhdu kotorymi osushestvlyaetsya za schet razlichnyh vremen relaksacii dlya verhnego i nizhnego lazernyh urovnei pri bystrom adiabaticheskom rasshirenii gaza. Na etom principe osnovana rabota gazodinamicheskih lazerov. Ochistka vozbuzhdennyh sostoyanii osushestvlyaetsya: spontannym izlucheniem; v stolknoveniyah s elektronami ili atomami primesnogo gaza, pri kotoryh energiya vozbuzhdeniya peredaetsya ot rabochego veshestva elektronam ili atomam primesi; pri adiabaticheskom rasshirenii gaza; v special'no podobrannyh himicheskih reakciyah. Takim obrazom, sreda s inversiei naselennosti sposobna usilivat' svetovuyu volnu. Pri koefficiente usileniya na edinicu dliny
![$\alpha$](https://images.astronet.ru/pubd/2002/04/10/0001175822/tex/formula9.gif)
![$I_2 = I_1 e^{\alpha l}$](https://images.astronet.ru/pubd/2002/04/10/0001175822/tex/formula10.gif)
![$G = e^{\alpha l}$](https://images.astronet.ru/pubd/2002/04/10/0001175822/tex/formula11.gif)
![$L = \lambda$](https://images.astronet.ru/pubd/2002/04/10/0001175822/tex/formula12.gif)
![$\lambda$](https://images.astronet.ru/pubd/2002/04/10/0001175822/tex/formula13.gif)
![$L \gg \lambda$](https://images.astronet.ru/pubd/2002/04/10/0001175822/tex/formula14.gif)
![$L \gg \lambda$](https://images.astronet.ru/pubd/2002/04/10/0001175822/tex/formula14.gif)
![]() |
Ris. 2. Principial'naya shema lazera. |
![$L = q \frac{\lambda}{2}$](https://images.astronet.ru/pubd/2002/04/10/0001175822/tex/formula15.gif)
![$\nu_q = q \frac{C}{2L}$](https://images.astronet.ru/pubd/2002/04/10/0001175822/tex/formula16.gif)
i rasstoyaniyu po chastote mezhdu sosednimi (q otlichaetsya na 1) modami:
![$\Delta \nu_{\Box} = \frac{C}{2L}.$](https://images.astronet.ru/pubd/2002/04/10/0001175822/tex/formula17.gif)
Na risunke 3 priveden chastotnyi profil' koefficienta usileniya v rabochem veshestve (on opredelyaetsya shirinoi i formoi linii rabochego veshestva) i nabor sobstvennyh chastot otkrytogo rezonatora. Dlya ispol'zuemyh v lazerah otkrytyh rezonatorov s vysokoi dobrotnost'yu polosa propuskaniya rezonatora
![$\Delta \nu_p$](https://images.astronet.ru/pubd/2002/04/10/0001175822/tex/formula18.gif)
![$\Delta \nu_{\Box}$](https://images.astronet.ru/pubd/2002/04/10/0001175822/tex/formula19.gif)
![$\Delta \nu_{\Box}$](https://images.astronet.ru/pubd/2002/04/10/0001175822/tex/formula19.gif)
![]() |
Ris. 3. Chastotnaya zavisimost' koefficienta usileniya v rabochem veshestve ![]() ![]() ![]() |
![$\alpha$](https://images.astronet.ru/pubd/2002/04/10/0001175822/tex/formula9.gif)
![$\beta$](https://images.astronet.ru/pubd/2002/04/10/0001175822/tex/formula22.gif)
![$\beta = \beta_1$](https://images.astronet.ru/pubd/2002/04/10/0001175822/tex/formula23.gif)
![$\Delta \nu_{\Box} > \Delta \nu_p$](https://images.astronet.ru/pubd/2002/04/10/0001175822/tex/formula24.gif)
Publikacii s klyuchevymi slovami:
lazer - kvantovyi usilitel' - kvantovyi generator - kogerentnost' - inversnaya naselennost' - mazer - spontannoe izluchenie - vynuzhdennoe izluchenie - nakachka - opticheskii rezonator - moda kolebanii
Publikacii so slovami: lazer - kvantovyi usilitel' - kvantovyi generator - kogerentnost' - inversnaya naselennost' - mazer - spontannoe izluchenie - vynuzhdennoe izluchenie - nakachka - opticheskii rezonator - moda kolebanii | |
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