Note: Descriptions are shown in the official language in which they were submitted.
2~ 9~052
~G:~ RESOLUTION AND S13:NSITIVITY IMAGIN(~ SPECTROGRAP~l
BacL;groutld of the ~ven~on
Field of 1he Illven~on
The present inven~on ~ene~lly rel~te~ to l~e ~ield of specl~oscopy, and
S more specifically relates to a high-rrc~ inn, bigh~ ul ~,~u~h.
Desc~tion ofthe Ba~L~uu.ld
Tm~7n~ UovU~ ~s nn ~ol~l tool in s~dying the cn~ros;~ n and
charact~ictirs of objects both near and f~ om mi~l~r~bl~ bin1n~cbl and
ch~miraI co,,1~uullds7 to the ~'5 ~ ~h~re~ distant stars and g~'l9~i~S. Por
10 the more d~stant objects, a spe~;hOgla~ iS the ~,.ef~1~d meaDs for ~h ~
~eir ~ ~cilinn~ as well as ck7~ ics s7lch as tu~ n1~ , radi~l velocity
and mq~n~tic field strellgth. The precision wi~ w~ioh these ll,ea~ ~e~l~ are
made ~epP~ c~ to a large extent7 on ~e spectr~l re~olv~inn ~e;hieved by the
n~h.
Im~ine speclluscol~y is also used to obtain spectr~ om r~l n~l~d
objects, such as eY1.~ .~1 plumes, expanding fireballs, clouds and gpl~riP5 By
no~ng c~n~es in 1he ~ecll~scûpic features a~ross an obje~t one can 1ean~ not
only the overall ch~--,t~ s of the object, but also the way in which ~ese
pJupel(ies change across it S~ecl~uscopes id~ the ç-ri-ct~n~e and/or the
locatinnc of individu~l feal~s and a cQII~ct~nn oft-hese f~ . A large field
of view is often needed to image l~rge ~ 9, while a smaller field of view is
".~f~l~d to ma~fy de~ils. ~t would be desirable to provide a spccllu~ayll ~at
allows the field of view to change without c~pn, .icin~ the resrlll1ion of the
~t
F~istin~ sl~e~,ll.J~lls typic~lly consist of a slit, which ~et~ r-s lhe
amount of light ~at enters the spectro~raph; a collnn~t~ r lens or mirror, wh~chfocuses the lightrays into parallel be s; a prism or grating, which .l;.~ c and
~e ligb~; ~nd a tclescope or objec~ve lens, which ~lu.luc~s a ~cc~
for visual observation Oc;~ nn~ one or more of the op~c~l cu ~ e.l~ of a
21 97052
~o~ph are c~...h..-P~l into one multi-purpose co.~ po~e ~1 A photographic
cameIa or o~er device may be in~ ld~d to record the ou~t of ~e s~e~lro~r~ph.
When irnaging ~ d sources, the ~hrou~hput of a s~c~v~h
sigrifican~ c on Ihe si~ of the slit used in ~e spec~ograph Wavelengll~
5 ~overa~e depends on a given slit's res.nllltion and s~ ilivily. Typically,
~roughput is illc~eased by ~ wider slits. Spe~tral resollltion ~ ., is
culll~o~ised by ~e wider slits. Acco,~.gl~, there i-s a need for a system tll~t
increases Ihluu~ l while re~ini~ hi~l re~olu~on.
Some s~echug~aphs use echelle ~ gs to ~ G and svyn~ al~ the light.
10 For example, T,P~t~ LabS PS se~ies sp~hull~ete~s use an echelle grating,
co...hil-r~ with a pnsm, to d~sper~e ~nd s~ "t; light over two ~1;m~nc;~ns
PYicti~ echelle ~ typically have a n 1~ ly coarse line sp~cing (e.g, 3~
150 l/mm) and are blazed atlarge angles (e.g., 60 - 7~~). These ~;,~s are often
used at large in~dent angles and ill hig~ diffiaction orders to achieve high
15 dispersion. At a given angle of dil~acLon many wav~ thc will be present
c~ h-~lku~cl~ due to order overlap. For a given r~nge of ~ !inn an~es it is
possible to have almost all the v~a~le~ om 3sooA to lOOOOA present
simultaneously. Fig. I is a plot of dif~action order 100 versus wav- le~ 110.
Notice ~at for v~a~ h~ less than 450û A, ~ere is some overlap 120 (i.e.,
20 ~o~e ..a~ ~C ~re ~ ed twice wi~in the dif~action angle). At longer
Wtl~ h~ (e.~, greater than 6000 A) gaps 130 in wavc1~,lh CO~ appea~.
As will ~e l1iccuc~ed next, ~ese gaps can be filled in by ~ the ~ngle of
ce (e.g.,.vt~ti..g~eg~ 1~.
Figs. 2 (a) and (b) display many specl~l lines of geoph~sical ~ ee
25 indlen~ elo~and~uronL TSel...;,~ 1 axis ofbotll~isthepixelsspace
~10, whe~e light having 10~ o~ h~s been i~aged o~to a 1024 x 1024 array.
Fig. 2(a) is ~e plot of ~a~. l ..UIh~ present an ~e deLe.,lol for the angle of int~ tt
DCOI 12to4~2
2 1 91052
i~ Fi~ 1. In Fig 2~b)~ ~e angle of ~c~ ~ ia 1~ less t~ ~at of Fig. 2(a). The
vertical lines ~ v~ e ~ ;;a~ e of ~ wavele~ at a p~colar pixel of ~he
...) ~e f~rstnumber 220 ~ e~ is ....~ h in ~ngs~oms (A), ~nd tlle
number in paren~h~s~s 230 inrli~ the difflac~on order.
S ~ rrine to Figs. 2(a) and (b), note that th~e is no discern~Y.e coITelation
L.c;L~een wavelength ~o and the pixel 210 where the ~.a~vle~ h is present.
F~er ~te ~t seve~l wavel~h~ (e.g., 7320 A (24) and 7990 A (22)) ~hat fall
into ffle ~s in ~ ~le~,ll, c~e 130 m ~i~. 1 are now ~le~ct~d following the
1 D rota~on ofthe gra~ing, as ev~len~ in Fi~. 2(b). A~ nn~lly~ note that some
f~,alulba (e.g., 3371 A in Fig. 2(b)) are present twice but at di~ orders,
inllic~ e lhe order overlap ~1;s~ sed earlier.
The spectral lines ~re sv~ c, locat;ed closely tQ~e~er, causmg
.r~ an~e~ ,lorastowhichwa~ isbeingdct~ Thisis shown
in ~ig. 2~D), where, at app,u,.i~atehy pixel 505, two ~ill~nt wav~ hc of light
15 arepresent Tobrulgthis~ hconfi~ nto~ lelevels,someorde}
sorting technlq~e is ordinalily elnploye~ unu~ typically use a cross
disp~b~g rl....rl~ to sep~ PIP ~e vaIiolls orders. Oft~ ~e cross Jisl~e.billg
rI~...F.I~t is anoth~ grating. This works ~ell for poin~ sources because ~e input
slit is ve~y sho~t, usually ~e sizc of the image of a star (e.g., less th~ S nlm). The
20 rf~nlltunt spec~ogram, ~r cross dispersing, has ml-lt pl~ spec1ra st~cked
vertically like n~s ~ a ladder. Similar ~ne~ ~e .~ are used in a~ n--lnir~l
rlir ~-inn!c Tbis tPrhniq~e howe~er, does not wo~ he case of an imaei~
s~l.. gr~l~ w~h a long slit where ~e ~mage of the slit fills ~e vert~cl ext~nt of
the ~l~it~,clor. Since Gon~ n~l echelle ~ ~uOJ..pbs employ a ~hort slit and
25 have a long focal len~ cnllin~ tl~r, the s1it h~s a s~ll anglllar height. I he ~e
of ~e sl~ therefore, occ ~ri~s only a small portion of the ~tP~tor ~ P ~ ir~
to ~e di~l~c.~lo" direction, causing mul~ple images of the slit to be stacked
DCn~
~1 ~7052
v~call~. ~e is a need, &er~fcr~, for an i~ that uses the en~e angular
field of the ~ r.
One attanpt to address ~is problem has been to limit tlle WaVC~ bl~lldS
the slit. This _ay be done by placing an ~ f~ ce filter wit~ m~lltiple
S tr~ncrni~cion ban~c in front of the slit or by havin~ ;yl~ slits, ea;ch with a di~erent filter. The latt~r ~ ;v~ provides ml.ltip~ .es of in~r.r
thereb~y providin~ fl~xibility in ~Ju~ g ~e des~ed wave1r~h~ Under ei~er
alt~n~tive~ ~the filters must have fa~rly broad (e.g., so-looA) ~ndp3cc
, r~ rs becallse of ~e angles encountered The effect of ~ese filters at ~e
10 ima~e plane is to block the u~ d orders and ~llow ~rpically only four or fiveorde~s to be ~ .05e~d Each line, however, has i~s c~u.~ ... plus &e
c.~ surr~n~ 11oftheotherlines. In~,u~.~ledpartsofthe
l~is is confilsin~ and, in the least, reduces the signal to noise ratio.
Another shul~;v~ of convention~l spect~ogr~phs is that the ~t~ctecl
15 ima{~es are 1~picslly noisy because of the small ~b~ of l~h~ q.~lled. The
detected unages may be illL~ d over a long period of ~me to reduce or
elimin~te the noise. Yet, for ~pplic~lions that reql~ire high l~ o.~l resolu~on
(i.e., high ~$~ inn m a short ~mount of t r le) ~ere is a need for a system that~llows the mtegr~lion ~ be L..v r". ~ed quickly. To have good ~ ~r~ ~snl~ltinh
20 (i.e., ~ tillteg ~iantime)the ~u~hD~sthave high Ih~u~ to be able
to record a large llu~b~ of ~holu~ dmillg the ~~ o~ period. ~.Yict1n~
devices fail to provide such ffinr.tif~nolity
Addition~lhy, culrent SIJ~G~aphS IJsed f~ a~u..~ -;e~l applications ~ave
not been able to achieve a h~h R~-cnl~ r ~ninCSity (~L) product, lC '~31tine
2s instead iII ei~r a ~,~u~aph ~Ivith high l~ hsiL~r, or a s~Lc1~ograph with hi~olv~ power, but not both. For a given ~ng, resolution and h..~.;..r.R:~y are
inversely plupo~1ional to ea~ er and are ffinctions of dle slit width and length,
D~OI .I~IOU~
2 1 97052
as well as ~e charaot~i~i~s of the collimator used. C~ al ~e~usc~pes
~pically ~ade l~l~ninosity for r~cn~ inn or vice versa by c~ pi~ the slit w~d~
andlor bi~ning pL~els on the ~et~ctnr. There is a need for a system that provides
both high luminosi~ and high ~solving power, i.e., an ~ t w~th a higb RL
5 product.
Furth~ re, c~ .e.,llu~a~,hs, due to their monotonic
wavelength cu~e and limited n~ber of a~ilable pixels, fi~r~ n ei~her as
survey in~ ls that cover a large por~on of the wavcl~l~glll (e.g., the en~e
visible range) at low resul~t;vn or as i~strumeIIts ~IF~ to a single srec?~l
10 feahlre (e.g., a few A wide) at high cpectrPl resoltltinn (e.g, less li~n 1 A).
However, many applications reql~ire the ~ lr~lus .lleasulclll~t o~ several
spec~l ~eab~es ~ ~l wa~l&l~g1L regions at moderate to high resolution.
Su-.. -.y ofthe Inven~on
It is therefore an object of the present invention to o~r~o~ ~ese and
o~er ~awl~dC]CS of the prior a~t and to provide a s~,e~".apl~ that provides hi~hspectral resolll~ir.n and la~e ~pec~l cove~e ~im~ sl~4!~1y.
lt is another object of the i~;o~ to i~ hlU!~ of a spec~ograph
while ~ ~Q~ n
It is allother object of the invell~ùn to permit a suffici~t amount of li~ht
to enter a s~)e~ osco~ sys~ thereb~ p~oviding fa~t i~ l;on t~me ~nd high
signal-to-noise ra~o.
It ~s a fur~er object of the mven~on to simplifi,r ~e co~huction of a
spec~ograph.
Tt is a fi~er object of ~e invention to allow the user to easily change ~e
field of v~ew of t~e spectrograph.
L~ 7
21 q1052
A ~ d . .ho~ of ~e inven~on is a hi~h-resolulio~, bigh-
~oughput i...aei~lg echelle ~yc~u~layll having a long slit. This embo-lim~t
yields high spec~al reso!~l~ion and large spectral c..~_...ge s~mult~o~ y. The
user is able to ma~e quick adj~ fn~C of the desired field of view. The
5 overlapping of di~erellt spec~al orders are sepal~led using a mosaic of
int~f. .~,..ce filters which ~n~ JAi~ 50 A ~rolmd the ~lf cl~ spectr~
lines. The spec~ corded by ~is ~nho~ e not lilce any other
~ec.L~oglaph where wa~elength increases or decreases mnnotQnieally along a
given di.~c1io~ ng d~ t~ ctul. lnstEad, only .~. lPCt. .~1 w~ndows about user
10 SPl~rtY~ pec~l re~ions a~e recorded ~ ml~ ~usly on ~e det~ctnr.
~ n another embodiment of tbe in~ention, ~e width of tbe slit is increased,~ereby ~lcl. as,.lg the i~ wll'S lhlv~l~ by ~u~l~dtely a factor of th~ee.
In another Pml-oAi".~,l of me in~ention, a mosaic filter ~it~ a limited
number of panels is provided. In ~is Pmho~;...e..l the ~ er of wavP1~.n~hc
15 observed ~ ously is limited, theleby achieving a larger wa~le~
coverage. ~ . .. ; v~ly, a mosaic f;lter havi~g a checkerboard pa~tem of ~tJcrs
is used, ~he~eby dividing the ve~tical dim~o.n~inn~ of the sli:t In ano~er
embo~ ..f-nl, a comb filter is used to p~ss nl~re l~an one ba~d of ligh~
rn another embo~lim~nt of the inven~on, filters are ...~ ..,t. A on a f~r
20 wheel or slide, enabling user~lefined modes of s~d~.
In another c~ o~iln~ ~-1 of the ~~ ul., a c~plPY ~lescope n~lo~. 5 the
field of view, ~us i~ ,&sing the spatial resnlnti. n without d~e-~h~g the
u~l~lyu~
In ano~er e -~l~o~ . e ~ of ~e invelltion, a plu~lity of det~ c~ are used
25 for in~n~ine ~e spcctral output
Another f .. I.o l;.. ~1 of ~e invention allows the u~ ;lv. e~iccinn
fe~..les from any part of ~e visible and near~ d sl,c~ cim~ o~.~ly.
DC01:1210U ~
~1 97052
In an ~lh ~ ;v~ e.lll o~ , the user can m-~nitor ~iccion features from ~y
part of the ultraviolet b~ cimlll~n~ollcly. All.,.~ ,ly, ~e user can
~nic~i~m feab res ~om any part of ~he i~an~d spe~ n~o11c1y~
O~er o~ject, adva~tages ~nd embo~ Pntc of the invention are set fort~
S ~n part in the desG~ ;on which follows, and in part will be a~pare~t ~om ~is
~sc~lion o~ ~om pl~lice of the ~nvcn~on.
Brief Des lion of the Dln~s
Fig. 1 ill~tes fhe order overlap result~ ~om a pnor alt echelle gra~ng,
Fig. 2(a) illu~ ,s lines of geo~hysical ~ n~e in the nieht~ w and
10 aurora ~letect~l bry a prior ut ~cc~ ph prior to order sorting.
Fig. 2(b) illu~l~ ~e lines of geophysical signi~cance in Fig. 2(a) af~er
dle incid~nt angle is ch~nE~I1 by 1~.
Fig. 3 is the layout of a pl~f~ d Mnbod; - e,ll of ~e invention.
Fi~. 4(a) illus~tes the S~ WU of Fig. 2(b) as ~l~t~ ry a ~lcL~
15 embo~limpnt of ~e inven~on.
~ ig. 4~b) illus~l~s 1~ ap~c~lu..l of Fig, ~(b) as d~tecte~ by a ~ler~ ,d
embo-lim~nt of ~he invention.
De~ tion of the I~,f~,l. d ~ b~
A ~l..f~ Ld embo~imerlt 400 of the present in~rention is ill~h~d in Fig.
3. This t'l~ O~ t 1~ iS generally ~ ""l" ;r A of f~w~tics 500, an op~cics and ~ilte~
mbly 600, a grating box 70n and a ~ clor 800.
I~e ~o~eo~ic~ 500 is eu...U. ;.~ of a ~ lens 510, a slit 520 ~nd a field
erLs 530, The optics and filter assembly 600 has a cotli~t~r 610, a f~rst i~ g
lens 6~0, a first follling mi~ror 630, a filter 640, a field lens 650, a second foldin~
mirror 660, a second ima~ng lens 670, and a canlera lens ~80. The ~ting box
700 inclu~es an echelle gra~g 710.
DCOI~1210~11 2
21 91~2
T~ ,..t lig~t e~te~s ~rou~h the primaIy le~s 510 l~he pnmary lens 510
focuses ~is light onto the slit 520. The field lens 530 l~di~ec~s the light Lo..d~ds
co~or 610. Collimator 610 causes the lightrays to become Fo~ d the
rays strike grating 710 wi~ ~n ~ngle of i~ n~e a and are dif3iacted at angle of
S dif~action ~. The di~.~ nce b~h ~ the angle of in~ nt a a~d t~e an~le of
dif~action ~ is a ~ le, ~. The light rays then travel to first
im~in~ lens 620, wbich is preferably placed close t~ t:he gra~g. The first
im~ne lens 620 focuses ~e r~ys on t~e fil~r 640.
Folding mirrors 630 ;~d 660 allow the size of ~e dence to be l~d~lced.
10 First foldin~ irror 630 reflects the light onto ~ r~no~rable or .I-t~h.. ~,Able
mosaic filter 640. Once the lightrays are filtered by filter 640, they travel Ihrou~
field lens ~50, ~e~ect off,0~second foldin~ mirror 660, and travel to ~cond
jm~~ lens 670. The second ;~n~ein~ lellS 670 and camera lens 680 refocus the
li~ht rays onto d~,t~,~,tur 8~0. The ~t~ tur 800 may be a CC~ detector or a s~r
15 d~te~ve device.
To get high ~ ugll~ul~ the ~rea~ le product (i.e., Inminocity) is
m~ i7r~1. A y~cr~lGd ell.bod; . e ~1 of the inven~on inr.hldes the longest slit
possible, 1~e widest sl~t that gives ac~ t~le resolu~on, and the fastest collimato~
d~ can be fillly i~ n~ted ~ the fo~oplics ~at a~e used to select l~e field of
20 view. Preferably, the lenses lhat change ~e field of view of the ~Ln~c,lt ~re al~l 35 mm c~leIa lenses. ~hese lenses can ill~inate ~n a~ u,~ t .ly 40
or ~0 mm long slit with liffle ~ttin~ Odler lenaes tha~ similarly ill.. il~ a
long slit with little Vi~ may be used.
1~ one embo~imeTIt, primaIy lens 510 is a 16 mm F/2.~ fisheye lens. The
25 i~ at~d circle is 40 ~ Pt~ with a 30% vi~ , at a field angle of
75~. CollimabDr 610 is ~ to match ~e F-number of the fi~;heye lens. Pecal~ce
CK'OI: -, 7
2 1 91052
a mirror collim~tnr with this small F-number would not have ~*~ll~te field
correction to image the 40 mm long (7.6~) slit, a ~efractiv~ et~,...~ .1 is used.
The u~lla~ of ~Lfr~c,ll spec~l orders are s~ 1 using a mosaic
of ~ r~lcnce filt~rs 640. ~ a ~l~rel~ed embo~ nt a mosaic of i~ .r~ ce
S filt~s is placed at~e image plane of detector 800. The filter i~ made up of strips
of individual filters made for specific wavel~n~hc In Figs. 4 (a) and (b), the
result of two mosaic filters are shown in relation to ~e lines that were
d~...n~ dted in Fig. 2 (b). The verlic~l dasSed lirles ~ '~l ~e bolm~ s of
the filters. The width of each b~J~a~s (e.g ylv~ ~ ly soA Full Wid~h at
10 Half Pow~ WHP)) is wide enough to admit preferably all of the ~
f3~t~ by~e physical width ofthe le~on on ~e ~ tcl~.f ~nd na~ow enough
to ~isrrimin~e y~ainst a~jace[lt orders. Pref~ably, the il~Le~l~ce ~ilters Ll~iLonly appro~;..,~t~ly soA around the seleet~d spectral lines.
~f a straight input slit is employed by ~e presellt inventia~ the ability to
15 co-add pLlcels of the CCD plior to readout in t~e vertical direc~on to select t~e
spati~l rrsnl hn nlay be co~lolllised. This iS bec~use the image of a straight
inpllt slit is curved on th~ CCD due to ~t;em~tism. The amount of c~atu~e is
a filn~tinn of the in~j~lPnt ~nd dif~action ~gles ~s well as the angular height ôf
~e slit ~ om the collimat~. To cu y~ .- t~, for this ~ m the im~ge
~0 of ~he slit is cuIved such that a chord u~nn~e!ine the ends of a creeh~l line would
be appr~ -c'~ly 1.5 nlm from a l~ne t~mgent to the center of ~e line, This
amount of curva~re would m~ke it difficult to use he mosaic filters d~~
above. Acco~J~ly, a preferred e~ af the invcntion uses a curved input
slit to null the curva~e of the image. A curved input slit mean~ that thc image
2s projected onto ~e scene by the foreoptics will also be cuIved. The m~
departure is ~ ;,Iably app1o~ ly 5~ for a l 80~ field of ~iew. Such a low
IZ1048,2
2 ~ 9~05~
c.u~,al~uG can be used ad~ ageo~y, such as when vie~ away from zeni~ in
nosrhf~rir studies.
Wavele~ does not increase or decrease ~ t~!~ically along a g~ven
direc~on on ~he ~g detect~r oft~e inven~on. Instead, on~y selectc(l windows
S ~bout u~r select~ble spec~al regions are ~corded .~ ;""~ o.~sly on dle det~ct~r.
The loca~on of each ~ he ~lPt~ct~nr has no di~-c~ tle patteln due to
the use of .L~e~ ec~1 orde~s for ~ t wav~1~n~th~
~ on ~e number of spec1ral lines and band passes around ~e liIIes
selected~ a p..,f~ ,d ~A.,bod~c.lt of ~he invention can record about 10-lS lineswith a~ uA;-~ ly 15-20~ ~reG~l region a~o~nd each at app.~ h l~ 0.4A
recnlnt;nn
Peak efficiencies can be as high as 0.8 for some gJ ~ s with a ~WHP of
~ ,ln,~ 10~ cel~tel.,d about ~e blaze direction when ~~aa.u~d in
Lit~ow mode. Groove shadowing may occur when the grating is u~ t large
15 incid~nt and dif~n ~les a~ well as when ~ere is a~plO~ ly a 20~ angle
beh.-ee~ ~he in~ nt and dif~acted beams. Such shadow~ng may cause about a
15% loss of ~ y when compared to Littrow mode. This loss can be
rd by .~Ju~g ~e 20~ angle bct~ ~e input and the ~f~act~,d beams.
Anodler embod~ment of the inver~on resol~es ~is problem by using a gnsm,
20 which is a b~Ctni~c~nn gra~ng on the sur~e of a la~e prism. This allows the
grating to bc used in Lit~ow mode and makes it easier to get ~he light from the
ends of ~e slitto ill~,...;l.4,~ ~e camera lens with ~ vi~
The m~~ y of the inve~on ~llows for parts to be quiclcly rep~ced or
"1~,..1r -.~;. d The ~u,c~tics camera lens may be affllched to tbe device using a
~5 standard 35mm camera ~:u~ ccliu4 thereby p~ ,.,uing the use of a vane~ of
lenses, ;...~ ; hl~u~es. The gra~ng box m~y be 1., .u~,d and replaced wi~h
a di~erent gra~ng box having ~ cl~ h~ ti~s The filter bo~ may be
2 1 97052
exch~nged for a ~ l type of fil~r. Finally, the detc tor n-o~lntin~ flange can
mm~ tçA one or several det~c~ devices.
The .1il~Pl-cio~c of ~e slit are adjustable. This allows the invention to be
operated in at least two modes. When ~he slit is narrow~ ~he de~nce oper~t~
5 high re~ollltinn mode, pro~idi~ a spectral resolu~on on the order of
~ fl~ 0.4 A and a spectral co~elage ranging froTn a~.u~ tely 4,000
to 10,000 A. When the slit width is mcreased, the device ~1)~ s in degl~ded
specl:ral rP~ m mode and the throu~hput is pl~r~l~ly increased by
appro~L;..,~tely a factor of three ~O~al~d ~vith the i~ment ~e~Li.lg in high
10 resolu~on mode.
Several types of filters ~4~ may be used. In one ~nbo~i~ent of the
invention, a mosaic filter with a chec~w~oard pattem is used. This di~ides ~e
c~ e of the sli~ and is usefi~l in cases where ~e scene has lit~le or
no spatial structure and ~ large number of spectral f~a~ s are being mnnitnred.
In another embodiment of the invention, a non-mosaic Slter having one
broad bo~ 7cs is u e~ This emho~;...P I allows a use~ to look at one order.
~ n ~nother em~o~ of the ilIven~on, a comb filter is used. The comb
filter is an il~t~r~l~ce filter wi~ m~ ip1e p~s b~nds. I'his ~llows a user to look
~t more ~an one band of li~h~
Other filters directed to a user's ~.. ,f~ cs or needs may also be used.
Moreover, a col~;,.~ion of the above ~Iters may b~e used.
In ano~her ~Tnho~ e ~t of the in~ention, a larger ~ covelage is
achieved by ~ ~ the ~u~r of ~. a~ C ob.~ d s~mlll~neously. The
fil~s ~re ~ .. t. -l on a filter wbeel or slide, therehy ~Iqhl in~ usels to choose the
25 c~hin~lion of spectral lines for a specific shldy. Since it is physically ~iffi~ t
to change fro~ one mosa~c filter to another if ~e filters were actually in closeuxi~ y to the det~ct )r, ~e spec~n is first ima~ed at a conve~ient size (e.g.,
2l0~a~
2~ 9~1052
50mm x 50rmn). The fi~ter w~eel is placed at ~e l~ inn w~ere the 5~C~ u iS
jma~d The filtered im~ge is then re imaged down to apJ)l~in~ately 15mm x
l~mm square CCD. T~is reduces dle r~nge of aD~es seen by the filter and keeps
the cross-over regions ~eh.~,.,n filters as naIrow as p~il,lc.
ThE invention may be used in ~i~glow and auror~l les~h ~om ~e
l~ation~l Science Foundation sponsored Polar Cap Obser~ato~y, and ma~ be ~sed
for low ~ ~e~ u5copic studies. The invention also ~r be used in a
num~erofmedical,en~ PntA1~and in~ applications.
Although the present invention ha~ be~n .1..~.i. ;l.ert in det~il, it should be
10 understood that v~nous r~ gpe~ s~lb~ ul;~ne~ d ~ItP~tione call be made
without d~ om the inbended scope as defined by ~e following claims.
210~.2
