B oth in terfaces are received at a ll times... Nguyen The Binh, Pham Van Ben,[r]
Trang 1B U IL D IN G A H IG H RESO LU TIO N S P E C TR O M E TR Y SYSTEM
W IT H LO CK -IN D E TE C T IO N TE CH N IQ U E
N g u v e n T h e B in h , P h a m V a n B e n , N g u y e n A n h T u a n , N g u y e n T r o n g T h a n h
D epartm ent o f Physics, College o f Science, VN U
A b s tr a c t, h ig h -re s o lu tio n s p e ctro m e try syste m ha s b e en b u ilt a t th e d e pa rtm e nt
M o n o c h ro m a to r G D M 1 0 0 0 a n d a D S P L o ck-in A m p lifie r S R 8 30 Se veral w orks
a n d re so lve d W ith hig h reso lu tion o f th e spe ctro g ra p h G D M - 1000 a n d high
s e n s itiv ity o f th e Lo ck-in a m p lifie r SR 8 30 , th is in stru m e n t is v e ry he lpfu l fo r
a n a ly s is o f m o le cu la r s p e ctra an d rese arch in m a te ria l s c ie n c e field
1 I n t r o d u c t io n
S tu d ies o f F lu orescen ce and R am a n scattering Spectroscopy alw a ys re q uire a spectrom eter o f h igh se n s itiv ity and high resolution W h en im p ro v in g an o ld spectrograph
G D M -1000 o f C a rlZ eiss/Je n a we stu d ied to design a n d con stru ct a spectrom etry system coupled w ith com p u te r u sin g L ock-in detection technique T h e m ajor advantage offered by lock-in a m p lifie r is the a b ility to reduce noise an d recover w eak signal U s in g a com puter for control, sy n ch ro n iz in g and processing increases a u tom atic c ap ability
2 E x p e r im e n t a l r e s u lt s
W e used a d ouble g ra tin g m onochrom ator G D M -1 0 0 0 o f C arlZ eiss/Je n a w ith the fist order spectra re g ion o f 7500cm '1 - 16675cm'1 (6000Ả - 13300Á) and the second o rd er spectra region o f 16675 c m1 - 28700 c m1 (3600 Ả - 6000 Â )
A fte r re m ov in g the auto recorder, a stepper m otor wa s used to control gratings (F ig l) O u r m ea su re m e n ts showed th a t one step o f m otor corresp on d ing to 0.0832 cm'1 of wave num ber T h e c ir c u it c o n tro llin g stepper m otor thro ug h p a ra lle l port o f com puter is shown in F ig 1 A sequence o f d ig ita l sigrial is sent to L P T port: 0001; 0011; 0010; 0110; 0100; 1100; 1000; 1001 correspon ding to position steps l-»2-»3->4->5-»6-»7-»8 D e ta ils of
"C o n tro llin g ste p p er through P a r a lle l P o rt" can be seen in reference [1]
W e used a S R8 3 0 D S P L ock-in A m p lifie r o f S tan ford Research System s to detect spectrum s ig n a l from P M T T h e SR830 L ock-in A m p lifie r m ay be rem otely program m ed via
e ith er the R S2 3 2 o r G P I B (IE EE -4 8 8 ) interfaces A n y com p u te r sup p o rtin g one o f these interfaces m ay be used to program the SR830 B oth in terfaces are received at a ll times
H owever, th e S R8 3 0 w ill send responses to o n ly one interface W e could specify the output interface w ith the [Setup] key o r use the O U T X com m and a t the b egin n in g o f every program to d ire ct the responses to the correct interface
Trang 2Nguyen The Binh, Pham Van Ben,
F ig l Schematic diagram of stepper controller
In th is research, a G P I B c a rd is used to com m unicate between co m p u te r a n d SR830 Before a tte m ptin g to com m unicate w ith the SR830 over the G P I B inte rfa ce, the SR830's device address m ust be set T h e address is set w ith the [Setup] key a n d m ay be set between
1 and 30 C om m u n ica tio n s w ith the S R8 3 0 use A S C I I chara cters C om m a n d s m ay be in eith er U P P E R o r lo w e r case a n d m ay co n ta in an y n um b e r o f embed space chara cters A com m and to the S R8 3 0 consists o f a fo ur chara cters com m and m nem onic, arg u m en ts if necessary, a n d a com m and term in ator T h e re isn't need to w a it betw een com m ands Th e SR830 h a s a 256 ch a ra cte r in p u t b uffer a n d processes com m ands in the o rd e r received
S im ila r ly , the S R8 3 0 has a 256-character o u tp u t b uffer to store o u tp u ts u n t il th e host com puter is ready to receive D eta iled com m and lis t can be seen in reference [2] A com puter program h as been made coding in V is u a l B asic to control a n d to process A sub for data a cq u isitio n and au to s en sitive in th is program is p resented bellow
Private Sub DalaAO ‘data acquisition A auto sensitive
Dim Malus As Integer
Dim I As Integer
Dim r As String
Dim s An Long
Call send (8 "OUTP73" status) • lest
Call entcr(r 255.1,8 status) ■maxlen=255
If Val(r) = 0 Then
Cali send (8 "SENS?", status)
Call cnler(r 255, ], 8 stains)
If Val(r) >= 14 Then
s = Val(r)- 14
Call send (8 "SENS" & Sir(s) siaius) ■set new sensiii\'e=oldSens-l4
Call send (8, "OUTP73 status) ■read R(Voh)
Call enter(r 255.1.8 -status) * enter r
End If
End If
For s = I To 27 ‘ Auto Sensitive
End If End If For s = I To 27 • Auto Sensitive
If (Val(r) >= aScns(s - 1 )) And (V;il(r) < aSenx(s)) Then Call send (8 "SENS" & Slrts -
I ) status) End If Next s Call scnd(8 "OUTP73" status) Call enter(r 255.1 8, sliiui.s) RcDim Preserve aR(nmcs + I ) nmcs = UBound(aR) aR(nmcs) = Val(r) ixt Watch.Texi = n2wn(nmcs) & " 1
" & r ' —>indicalor
End Sub
Trang 3In o u r laboratory, a n A rg o n Ion L a s e r (C W , w a velength o f 488nm a n d 514.5nm, pow er o f 2W), a N itro g e n Lasei- (repetition rate o f 10Hz, p ulse w id th o f 9ns) a n d m ercury lam ps w ere used as e xcitation sources fo r fluorescence o r R a m a n sca tte rin g studies A n
o ptical system o f o p tim a l con d itio ns fo r sam ple illu m in a tio n w a s also studied To exam ine the function o f th e achieved spectrom etry system w e recorded photolum inescence spectrum
o f n a tu ra l ru b y excited by an Ư V L E D (Fig.2a) T h is spectrum shows two peaks, w hich agree w e ll to d ocu m en tation s about the n a tu ra l ruby F ig,2b show s the r a d ia tio n spectrum
o f the u v led
F ig 2 a- Photoluniinescence spectrum of natural ruby sample,
b - Radiation spectrum of the u v led
3 C o n c lu s io n s
T h e spectrom etry system coupled w ith com p u ter u sin g L ock-in detection technique
wa s b u ilt at o u r laboratory S evera l w orks con cern in g w ith cou p ling , processing d a ta and spectrum c a lib r a tio n w e re stu d ied and resolved The achieved spectrom etry system w ith
h igh s en sitivity a n d re so lu tio n is very h e lp fu l in stru m e n t for us to stu dy la ser spectroscopy such as laser R a m a n scattering, la ser induced fluorescence to research m ole cula r stru ctu re and o ptical p ro pe rties o f sem iconductor m aterials
Acknow ledgment. T h is w o rk w a s supported by the special project Q G -04 o f the scien tific research program o f V N U
R e fe r e n c e s
1 Bhaskar G upta, Understanding various types o f Stepper Motors A nd Controlling it through Parallel Port, Homepage: http://collection.sharewith.us (2004)
2 Stanford Research Systems, Model SR830 DSP Lock-in Amplifier, (1993), 5.1 - 5.34