I) Gii thiu 1.Khi nim Phn cc thng:nu in trng ca chn ng sng c mt phng dao ng khng i theo thi gian th nh sng c gi l phn cc thng Phn cc trn:nu trong qu trnh truyn sng vect in trng E ca nh sng thay i sao cho u ca vect E vch thnh mt ng trn xon c trong khng gian th nh sng c gi l phn cc trn. Phn cc elip: nh sng c u vect in trng E vch thnh ng xon c elip c gi l phn cc elip vnh sng t nhin: c vect E dao ng u n theo mi phng vung gc vi tia sng. v nh sng phn cc: + nh sng phn cc ton phn : C vect E dao ng theo mt phng nht nh vung gc vi tia sng. + nh sng phn cc mt phn : C vecto E ging nh sng t nhin nhng c phng dao ng mnh, c phng li dao ng yu. 2.Ni dung -Phn loi Phn cc bi hin tng lng hng sc: Phn cc bi hin tng lng chit Phn cc do phn x Phn cc do tn x II)ng dng Mt trong nhng ng dng thng dng v thc t nht ca s phn cc l s hin th tinh th lng (LCD) dng trong hng lot dng c nh ng h eo tay, mn hnh my tnh, ng h bm gi, ng h treo tng v nhiu vt dng khc. Cc h hin th ny da trn s tng tc ca cc phn t kt tinh cht lng dng que vi in trng v sng nh sng phn cc. Pha tinh th lng tn ti trng thi c bn c gi l cholesteric, trong cc phn t nh hng thnh lp, v mi lp k tip th hi xon mt cht to ra hnh dng xon c (hnh 9). Khi sng nh sng phn cc tng tc vi pha tinh th lng, sng b xon li mt gc gn 90 so vi sng ti. ln chnh xc ca gc ny l hm m ca pha tinh th lng cholesteric, n ph thuc vo thnh phn ha hc ca cc phn t (c th c iu chnh tinh t bng s thay i nh trong cu trc phn t).

Mt v d l th v ng dng c bn ca tinh th lng vi cc dng c hin th c th tm thy trong s hin th s tinh th lng 7 on (minh ha trong hnh 9). y, pha tinh th lng nm kp gia hai a thy tinh c gn in cc, tng t nh miu t trong hnh. Trong hnh 9, cc a thy tinh nh hnh vi 7 in cc mu en c th tch in ring r (nhng in cc ny l trong sut i vi nh sng trong dng c thc). nh sng truyn qua bn phn cc 1 b phn cc theo chiu ng v, khi khng c dng in p vo cc in cc, pha tinh th lng gy ra gc xon 90 ca nh sng cho php n truyn qua bn phn cc th 2, bn 2 b phn cc ngang v nh hng vung gc vi bn phn cc 1. nh sng ny khi c th to nn mt trong by on trn mn hin th. Khi dng in c p vo cc in cc, pha tinh th lng sp thng hng vi dng in v mt i c trng xon c cholesteric. nh sng truyn qua mt in cc tch in khng b xon v b chn li bi bn phn cc 2. Bng cch phi hp in th trn by in cc dng v m, mn hin th c kh nng biu din cc s t 0 n 9. Trong v d ny, cc in cc pha trn bn phi v pha di bn tri c tch

in v chn nh sng truyn qua chng, cho php to ra s 5 trn mn hin th (nhn ngc li trong hnh 9).

Knh lc phn cc cng c s dng trong nhip nh thu c mu xanh m hn cho nn tri hoc loi b cc nh sng phn cc phn x li t mt nc hoc t ca knh

Hnh bn tri l nh chp thng thng, hnh bn phi l nh chp cng mt cnh nhng c s dng knh lc phn cc.

.

Vi mt s vt liu trong sut, di tc ng ca lc ko nn (hoc cc tc ng vt l khc, nh tc ng ca in trng, t trng, ...) vt liu c th th hin tnh lng chit. Do sc cng trong lng vt liu, hoc cc tc ng vt l ln vt liu, c th c quan st khi ri nh sng phn cc ln vt liu v s dng knh lc phn cc u ra ca chm sng sau khi i qua vt liu.

Sc cng bn trong lng mt min thy tinh c thy r khi quan st di nh sng phn cc, thng qua knh lc phn cc.

Nhng ng dng khc ca nh sng phn cc bao gm nhng chic knh rm Polaroid ni trn, cng nh vic s dng cc b lc phn cc c bit dng cho thu knh camera. Nhiu thit b khoa hc a dng s dng nh sng phn cc, hoc pht ra bi laser, hoc qua s phn cc ca cc ngun nng sng v hunh quang bng nhiu k thut khc nhau.

Cc bn phn cc i khi c s dng trong phng v chiu sng sn khu lm gim nh chi v tng ri sng, v mang knh cm nhn chiu su vi nhng b phim ba chiu. Cc bn phn cc bt cho cn c dng trong b qun o du hnh v tr lm gim t ngt kh nng nh sng pht ra t Mt Tri i vo mt ca nh du hnh v tr trong lc ng. S phn cc nh sng rt c ch trong nhiu mt ca knh hin vi quang hc. Knh hin vi nh sng phn cc c thit k dnh cho quan st v chp nh cc vt nhn thy c ch yu do c trng bt ng hng v mt quang hc ca chng. Cc cht d hng c tnh cht quang hc thay i theo hng truyn ca nh sng i qua chng. hon thnh cng vic ny, knh hin vi phi c trang b c bn phn cc, t trong ng i ca tia sng trc mu vt, v bn phn tch (bn phn cc th hai), t trong quang trnh gia l sau vt knh v ng quan st hoc cng camera. S tng phn nh tng ln do s tng tc ca nh sng phn cc phng vi cht lng chit (hoc khc x kp), to ra hai thnh phn sng ring r phn cc trong nhng mt phng vung gc vi nhau. Vn tc ca cc thnh phn ny khc nhau v thay i theo hng truyn nh sng qua vt. Sau khi ra khi vt, cc thnh phn nh sng lch pha nhau v qut nn mt hnh elip vung gc vi hng truyn, nhng kt hp li qua s giao thoa tng cng v trit tiu khi chng truyn qua bn phn tch. Knh hin vi nh sng phn cc l k thut nng cao tng phn ci thin cht lng nh thu c vi cht lng chit khi so vi nhng k thut khc nh s chiu sng trng ti v trng sng, tng phn giao thoa vi sai, tng phn pha, tng phn iu bin Hoffman, v s hunh quang. Ngoi ra, vic s dng phn cc cng cho php o c nhng tnh cht quang hc ca khong vt v cc cht tng t v c th gip phn loi v nhn dng cc cht cha bit. III)ng dng trong nhip nh

Polarizers Filter:nh sng di chuyn theo dng sng, tt c cc vt th u phn x nh sng v ng knh ghi nhn tt c cc loi sng nh sng phn x . Trong qu trnh phn x, cc sng nh sng phn chiu ny c th cng hng hoc gy nhiu ng sng nh sng kia gy ra lo sng v bng nh. Bng cch xc lp trc truyn ( xoay filter ), Polarizers Filter s cn nhng tia sng do phn chiu (unpolarized ) bng cch y ra ngoi , ch cho php nhng tia sng c phng vung gc ( perpendicular ) tia sng phn chiu i vo ng knh (P-Polarized ), hn ch cc sng nh sng phn chiu lung tung "free to move. Do sng nh sng t cc

vt th khng phn chiu ( non-metallic surface) phn cc i vo ng knh c lc b i s nhiu ng do s phn chiu t vt th khc. V d nh ch th ang vng mt nc ( hoc trc mt knh ) Polarizers Filter s loi b s m ( veil ) bn ngoi to cho nh sng truyn t ch th vo ng knh mt cch trung thc, mu sc v nt c bo ton phn no.

Tht l kh, nu chp nh mt ch th ng trc hoc sau b mt phn chiu m khng dng Polarizers Filter, v ng knh s ghi nhn ton b nh sng k c nh sng ca s phn chiu khng mong mun. Rt hiu qu nu ta dng filter ny chp nh cc vt th trc gng hoc mt nc k c di bu tri sng chi, Polarizer Filter s loi b nhng nh sng do phn x m c, gi li nh sng t cc vt th khng phn chiu ( non-metallic surface)

Linear Polarizers Filter:

y l loi filter c lp film vi nhng li dy song song wire grid ( B+W ) n s cn v phn chiu ngc ra ngoi nhng tia sng ln xn ramdomly polarized / unpolarized, nu t nm ngang n s cho php ch nhng tia sng phn cc ng ( vertically polarized beam light ) i qua, tng t vi t theo phng ng, hoc nu t theo phng 45 th n ch cho nhng tia phn cc 135 i qua.

Filter ny c cng dng chnh l cn nhng tia sng phn x, tng tng phn, tng bo ho mu. Bi v filter ny cn sng theo kiu cut off nn s gy nn hin tng o sng v ly nt sai trn my nh in t . Do , filter ny khng thch h p khi b n s d ng cc my nh i n t v i ch l y nt t ng ( AF ) . Nhiu hng ch to filter khuyn co khng nn s dng Linear Polarizer Filter trong cc ch ly nt t ng AF v o sng TTL Meter ( nn chuyn v ch ly nt tay MF )

Circular Polarizer Filter - CPL:

Filter ny l loi ci tin t Linear Polarizer, n bao gm 2 element, thnh phn th nht pha trc l Linear Polarizers Filter, thnh phn th 2 pha sau c gi l Quarter Wave Plate ( Quarter l gc mt phn t, cng c hng gi l half-wave Plate ), cc tia Polarizer i qua thnh phn th nht v di chuyn qua thnh phn th 2 theo ng xon c ngc chiu kim ng h vo pha trong. Hin ti, cc hng sx Filter ln v ni ting khng cn dng lp plastic cho Linear Polarizer Filter m thay vo l lp thu tinh mng gi l glass-to-air hay foil-to air surface do theo khuyn co khng c b mt ca CPL nng hn 70 C ( hoc 158 F ), do vy nhng n flash gn ln pha trc ng knh ( flash dnh chp macro ) khng nn s dng i cng vi CPL.

S dng CPL rt hiu qu khi chp nh m ch pha trc mt nc, knh, kim loi gy phn chiu, ngoi ra n cn gip cho bc nh trong hn, mu sc p hn. a phn cc sn phm CPL u c mu xm trung tnh ( Neutral ) tuy nhin vn cn c nhiu loi khc, do vy khi la chn CPL nn ch thm k hiu ghi trn filter. V d:

B+W Linear & Circular Polarizers KR 1.5, y l CPL ci thin chi tit vng mu m v cho ra tone mu m. ( Tng t KR 3, n s cho ra tone mu m mnh hn ) B+W CPL Pro Redhancer : y l CPL ci thin chi tit vng mu nng v cho ra tone mu nng. Filter ny rt thch hp cho nh phong cnh ma thu vng bc bn bn cu ( Chu u Bc M ), nhng rng cy l phong s p hn, mu golden s ti hn vv