IR Athermal Achromat Design

Transcription

1 08 July 09 IR Atherml Achromt Design Presented to: Optics Wesite Presented y: Willim H. Plin Rod South Deerield, MA 0373 Tel: Fx: Emil:

2 Ojectives Provide the theoreticl sis or the design o n therml chromt Illustrte design process or n therml chromt Present seline MWIR singlet design perormnce Present design perormnce o MWIR therml chromt

3 Technicl Approch, Prt I: Eqution Development Derive eqution which yields chnge in lens ocl length vs. temp. in terms o the lens vriles: rdii o curvture thickness rerctive index Write eqution or thermliztion or two thin lenses in contct Derive eqution or chromtiztion or two thin lenses in contct Solve thermliztion & chromtiztion equtions simultneously to get the required lens glss & therml properties to design thermlly stle doulet chromt

4 Technicl Approch, Prt II: Design Appliction o the Mth Tulte cndidte glss opticl nd therml properties: Rerctive index, N Ae numer, Therml coeicient o expnsion, TCE Chnge in rerctive index vs. temp., dn/dt Lens therml coeicient, LTC /(N) Clculte numer nd LTC rtios o the crown & lint glsses Serch out glss comintions which yield numerltc rtio mtch Develop rel lens design sed on glsses which yield est mtch

5 Thick Lens Focl Length vs. Temperture Dioptric power, Φ, o thick lens is given y () : é t(n (N ) ê + ër R NR R ) ù û lens ocl length t lens thickness R lens irst surce R lens second surce rdius Chnge in dioptric power, Φ, with temperture, T: dt d dr dr dt dn R dt R dt t dt N dt () Thick lens eqution cn e simply derived rom sic irst optics reltionships; see, e.g., Smith s ook, Modern Opticl Engineering

6 Chnge in Lens Power vs. Chnges in riles R R é N ù ê + R ë û dt é t(n (N ) ê + ër R NR R d ) ù û dr dr dt dn R dt R dt t dt N dt R t R (N ) NR R é N ù êë R û N + N t(n ) N R R

7 Chnge in Lens riles vs. Chnge in Temperture dt é t(n (N ) ê + ër R NR R d ) ù û dr dr dt dn R dt R dt t dt N dt dr dr dt R R tdt dt dt dn dt

8 Chnge in Lens Power vs. Chnge in Temperture dt é t(n (N ) ê + ër R NR R d ) ù û dr dr dt dn R dt R dt t dt N dt Introduction o the clculted derivtives into the ove eqution gives: For thin lens, d dt d é ù N + t dt êë N û N R R é» êë ù N û Approximtion yields suicient ccurcy or norml singlet lenses* * For exmple, 99% ccurcy or dφ/dt is chieved or lens o 5 mm thickness, 00 mm ocl length, R R 00mm, nd N.5 when the thickness is ssumed to e zero in lieu o the ctul 5 mm vlue.

9 Athermliztion Condition or Singlets & Doulets For singlet: d dt» é êë ù N û Singlet lens is therml when dφ/dt 0, i.e., when α /(N) Dioptric power o doulet comprising Element nd Element : + Chnge in power o doulet vs. chnge in temperture: d d d + dt dt dt Doulet lens is therml when dφ / dt 0, i.e., when é ê ë ù N û ù N û é ê ë 0

10 Thin Lens Axil Chromtic Aerrtion (Longitudinl Color ) d d æ ç è d ö ø é ê ër R ( N ) (N ) K d dl d dl d l d dn dn dl dn K dl l KdN l ù û l d dn l 0 K é K ê ër N N N 0 R N ù û l 0 N ( N ) l l Axil Color: directly proportionl to lens power inversely proportionl to glss Numer (Ae Numer) 0 N l

11 Axil Color Correction in Thin Lens Doulet Lens Element Lens Element Power o the doulet: + Axil color o the doulet: d, Axil color is eliminted when d , :

12 Simultneous Axil Color Correction & Athermliztion o Thin Lens Doulet û ù ê ë é û ù ê ë é N N + Lens Element Lens Element Power o the doulet: Axil color correction exists when: Athermliztion exists when: Simultneous color correction nd thermliztion exists when: û ù ê ë é û ù ê ë é N N LTC or Glss LTC or Glss

13 Simultneous Axil Color Correction & Athermliztion o Rel Lens Doulet The ollowing mteril is presented in support o rel world MWIR thermlized chromt design exmple. Silicon Singlet Reerence Design Aerrtions/Therml Deocus. Cndidte Lens Mterils, 35 μ Wvend 3. MWIR Achromt Cndidte Glss Comintions 4. Silicon Germnium Achromt Lens Element Powers 5. SiliconGermnium Doulet Aerrtions/Therml Deocus

14 Silicon Singlet Reerence Design EFL00 APERTURE50 Silicon singlet exhiits very lrge mount o primry xil color

15 Silicon Singlet Reerence Design Therml Focus Shit SILICON SINGLET REFERENCE DESIGN (EFLF/ 00mm) Focus Lens Trvel (mm) vs. Temperture nd Oject Rnge Rnge(m) Temperture (Deg. C

16 MWIR Doulet Achromt Exmple: Cndidte Lens Mterils, 35 μ Wvend Glss Type N l4.00nm Numer Therml "D o " Therml Lens (Zemx) 35nm Coe (dn/dt ctor) Rer. Index Therml Wvend () Expnsion Coe () Coeicient (LCE) dn/dt (/(N) ( x 0 6 deg. C ) ( x 0 5 deg. C ) ( x 0 6 deg. C ) AMTIR AMTIR CAF CLEARTRAN GERMANIUM GE_OLD IRG SAPPHIRE SILICON ZNSE ZNS_BROAD () Therml rerctive index coeicient is relted to Do (See Zemx Mnul Therml Anlysis Chpter) () Numer is deined s: N l 3.75nm l 4.75nm Glsses shown in tle ove comprise the min choices ville or lens design in the MWIR nd..dt rom Zemx glss ctlog N Germnium & Silicon exhiit very good mtch etween Numer & LTC rtios Exct mtch yields simultneously ull chromtiztion nd thermliztion N l 4nm Note relted to glss ctlog glss property D o, vi mteril rerctive index: D o /[N/(N )]

17 MWIR Doulet Achromt Exmple: Cndidte Glss Comintions Lens Element Lens Element Cndidte Glss Comintions, MWIR Achromt Lens Element Power, Unity Power Achromt (Focl Length ) Atherm/Achrom Mtch Fctor, M / LTC / LTC M ( / ) / "Crown" Glss "Flint" Glss "Crown" Element "Flint" Element (LTC / LTC ) Element"" Element "" Power ( ) Power ( ) SILICON GERMANIUM SILICON CLEARTRAN SILICON ZNS_BROAD ZNSE GERMANIUM ZNSE CLEARTRAN ZNSE ZNS_BROAD SiliconGermnium glss comintion is the est choice: Atherm/Achrom Mtch ctor nerly perect (.0) No other glss comintion pproches this degree o mtch Low element powers cilitte correction o errtions SiliconGermnium comintion yields thermlly stle chromt

18 MWIR Doulet Achromt Exmple: Silicon Germnium Lens Element Powers Lens Element (Silicon) Lens Element (Germnium) Power o Element (Silicon) or Unity Power Doulet (Φ, ): Power o Element (Germnium) or Unity Power Doulet (Φ, ):

19 MWIR Achromt Exmple: SiliconGermnium Doulet Aerrtions SiliconGermnium comintion yields very high degree o chromtism

20 SiliconGermnium Doulet Therml Focus Shit SiliconGermnium Doulet (F/, EFL00) Rnge(m) Focus Lens Trvel (mm) vs. Temperture nd Oject Rnge Temperture (Deg. C

21 SiliconGermnium Doulet, 5mm Aperture Improved Axil Color Correction EFL 00 mm Aperture 5mm SiliconGermnium doulet with reduced perture (5mm vs.50mm) yields improved xil color correction

22 SiliconGermnium Doulet, 5mm Aperture Therml Focus Shit EFL 00 mm Aperture 5mm Δ Ryleigh o deocus l (FNo) (0.004mm) (00/5) 0.8mm SiliconGermnium Doulet (5mm Aperture) Focus Lens Trvel (mm) vs. Temperture nd Oject Rnge Rnge(m) Temperture (Deg. C) SiliconGermnium doulet with reduced perture (5mm vs.50mm) yields reduced therml deocus..imperceptile y Ryleigh criterion Axil color nd therml ocus shit re tied together.s color correction improves so does therml ocus stility

23 Summry Equtions re derived which provide guidnce in the selection o two glsses which will yield simultneous correction o the xil color errtion nd therml deocus in doulet chromt Selection criteri or the glsses re: > Ae Numer (Numer) > Index o rerction > Therml Coeicient o Expnsion > Chnge o rerctive index with temperture, dn/dt Design procedure or rel world MWIR doulet is given Perormnce o the rel world doulet (EFL00mm) is presented: Axil color errtion is negligile (OPD < l/0) Therml deocus rom 40 C to +80 C is < Ryleigh unit SiliconGermnium chromt yields simultneous color correction nd reedom rom therml deocusing unique design solution