EN_OPUS 6.0 STEP.book
Contents
1. 8 4 1 General Information ta a taa awk 8 4 2 Setting up the internal ADC e id pi AA ao 8 4 3 Setting up Measurement Parameters 0 0 cece eee 10 4 4 Starting the Measurement praia an 12 4 5 3D Corelation AAA ay ee ae Seen ee 13 5 Time Resolved Step Scan with a Transient Recorder 13 5 1 General Information 4 3 5 Anew ey aa oe e a eee oe A BAS 13 5 2 Setting up the Transient Recorder nariicaion Dinan tei et eee an a 14 5 3 Setting up Measurement Parameters n n nunnana cece cee eee ee 15 5 4 Starting the Measurement dr a a a ds 19 1 Introduction The OPUS STEP software package allows a wide range of kinetic and modula tion demodulation experiments based on the step scan technique In contrast to the normal Rapid Scan mode of data acquisition with an uniform interferometer mirror speed in the Step Scan mode the interferometer mirror is moved from one optical retardation position to the next in a stepwise manner and data is acquired at each position Typical applications of the Step Scan technology are e Photoacoustic spectroscopy PAS measurements with variable mod ulation frequencies depth profiling and photothermal beam deflec tion e Modulation demodulation experiments where the dynamic spectral response of the sample to a perturbation is determined e Time resolved spectroscopy TRS to pursue rapid dynamic phenom ena into the nanosecond domain Time resolved step scan measurem2. dows refer to the OPUS Reference Manual Bruker Optik GmbH OPUS STEP 15 Time Resolved Step Scan with a Transient Recorder Step Scan Time Resolved Measurement E x H Basic Advanced Optic H Acquisition FT Check Signal Device PAD82B z m Sampling Time Resolution Number of Timeslices fico Timebase Compress to Log Timescale Input Range 0 400mv Repetition Coadd Count E Trigger Mode intemal y Experiment Pre Post Trigger fo points Experiment recovery time fro ms Stabilization delay after stepping ao ms Second Channel Use for Weighting discard if lt Threshold d Threshold 06 Second Channel Input Range 500 d Exit Cancel Help Figure 7 Step Scan Time Resolved Measurement Dialog Box Recorder Setup Device Select the transient recorder that is actually connected to your spectrometer from the Device drop down list This list contains all devices that are listed and checked in the Devices Option dialog window figure 6 Time Resolution In case of internal triggering the Time Resolution is the time interval between detector output digitizations and consequently also the time interval between subsequent timeslices or spectra The maximum time resolution is 5us Do not enter a larger time resolution value also in case of external triggering Number of Timeslices This value represents the total number o
3. 3D Correlation The raw data are calculated using the defined FT parameter and then stored automatically in the desired data block type containing the single time slices of the time resolved measurement in chronological order and the FT parameters of measurement 4 5 3D Correlation To perform a 3D correlation the 3D software package is required This software allows you to correlate dynamic spectra that describe the spectral changes of a sample exposed to external perturbations that in contrast to the modula tion demodulation technology need not necessarily have the shape of a sine function The result of a 3D correlation is a new 3D file The correlation relation is illustrated in a 3D plot with two wave number axes This type of plot allows you to determine the synchronous and asynchronous correlation spectra directly from the run time of the changes in the spectra without using a lock in amplifier and a sine modulation frequency For detailed information refer to the 3D software manual 5 Time Resolved Step Scan with a Transient Recorder 5 1 General Information This option allows the study of extremely fast physical phenomena in the nano second domain using a transient recorder It requires special hardware and the OPUS STEP software package We also recommend the OPUS 3D software package to display the results in stacked plot and contour plot views During this fast type of time resolved measurement the interferogram i
4. OPUS Spectroscopy Software User Manual STEP gt lt BRUKER LK 2006 BRUKER OPTIK GmbH Rudolf Plank Str 27 D 76275 Ettlingen www brukeroptics com All rights reserved No part of this publication may be reproduced or transmitted in any form or by any means including printing photocopying microfilm electronic systems etc without our prior written permission Brand names registered trade marks etc used in this manual even if not explicitly marked as such are not to be considered unprotected by trademarks law They are the property of their respec tive owner The following publication has been worked out with utmost care However Bruker Optik GmbH does not accept any liability for the correctness of the information Bruker Optik GmbH reserves the right to make changes to the products described in this manual without notice This manual is the original documentation for the OPUS spectroscopic software Table of Contents 1 Introd cti m si eee w eed E ciwe R 1 2 Hardware Requirements ccc cece cee cere cee eee eee 1 3 Step Scan Modulation 5 gs 5 4 0 s0 9205 a os Nw ew ES 2 3 1 General Information lv ace ein tae WANG a aad Ge RE Bea aS 2 3 2 Setting up Measurement Parameters 00 unauna 2 3 3 Starting the Measurement 4 5 acd enk oes beA iS da 7 3 4 Overflow Detection during the Measurement 0 00005 7 4 Time Resolved Step Scan with the internal ADC
5. A ADC 8 Amplitude demodulation angle 5 Amplitude modulation 2 4 5 Amplitude modulation frequency 5 B Bessel function 4 C Compress to log time scale 17 D Discard experiment if 19 DSP 2 3 4 DSP demodulation 5 E Experiments recovery time 8 12 13 18 External LIA 3 External timebase 11 17 External trigger mode 12 17 H Hardware requirements 1 I In phase 5 6 Input range 11 17 Interferometer mirror 3 4 8 13 Internal ADC 8 9 10 Internal trigger mode 12 17 ISA slot 1 L Linear timescale 11 Lock in amplifier 2 3 5 6 13 M Modulation amplitude 4 Modulation frequency 4 13 Multiple channels 6 N Number of coadditions 3 Number of timeslices 8 11 13 16 O Overflow detection 7 P Phase demodulation angle 5 Phase modulation 2 4 5 Pre Post trigger 18 Q Quadrature 5 6 R Repetition coadd count 8 11 13 17 S Second channel 18 Signal to noise ratio 11 12 17 18 Single channel 6 Stabilization delay 3 4 8 Stabilization delay after stepping 12 13 18 Step scan modulation 2 T Time resolution 8 11 14 16 18 Time resolved step scan 8 13 Timebase 11 17 Timescale 17 Transient recorder 14 13 17 Trigger mode 12 17 U Unused 18 Use for phase correction 18 Use for weighting discard if 19 Use second channel for weighting 19
6. selection of the modulation frequency depends on the experiment PAS measurements allow the analysis of various sample layers by variations in the modulation frequency high frequencies are used to analyze sample layers near the surface while low frequencies are suitable for analyzing deeper sample regions The drop down list Modulation Frequency contains all possible modulation fre quencies as integer values Note that only discrete modulation frequencies are available So if you enter a value instead of selecting an option the entered value is corrected automatically by the TC 20 controller The actual applied modulation frequency is stored with the instrument parameters in the created file The generated modulation frequency is available as a TTL signal at the Ref out BNC plug of the I O cable Modulation Amplitude Performing a phase modulation changes the shape of the resulting spectrum The shape depends on the amplitude of the applied phase modulation In fact the normal single channel spectrum appears to be multiplied by a first order Bessel function J 2mve of which the argument contains the product of the modulation amplitude and the wave number v This function is zero if ve 0 The first and largest maximum is reached at ve 0 29 and the first zero crossing occurs at ve 0 61 At higher wave numbers this function oscillates with decreasing amplitude around zero To ensure that the entire spectrum of interest is above the f
7. a string like 0 Jnternal ADC figure 3 The number at the beginning of the string 0 in the given example must be entered it indicates that the device in the list is unique The string on the right hand side of the equals sign must contain the substring ADC other additional substrings are optional After entering the correct string click on the OK button On the Optic Setup and Service dialog fig 2 click on the Save Settings button Devices Options E x Transient Recorder 3 PAD82 M 4 PAD1232a 5 PAD1232b M 6 P4D1232c W O Intermnal ADC Item UP Item DOWN Edit Item Add New ltem Delete Item Restore Factory Defaults Figure 3 Devices Options Dialog Box Setting up the internal ADC Bruker Optik GmbH OPUS STEP Time Resolved Step Scan with the internal ADC 4 3 Setting up Measurement Parameters Select in the OPUS Measure menu the Time Resolved Step Scan function The Step Scan Time Resolved Measurement dialog box opens Basically this dialog box is identical to the Measurement dialog box described in the OPUS Refer ence Manual except for the Recorder Setup page Click on the Recorder Setup tab The dialog window shown in figure 4 opens It allows you to define the necessary parameters to perform a time resolved step scan measurement Note Before starting a measurement ensure that all parameters are set correctly For detailed information on the measurement paramete
8. ash of light does not ignite 5 4 Starting the Measurement To start the measurement click on the Basic tab and then on the Start Step Scan Time Resolved Measurement button If the parameters Resolution Phase Resolution Wanted Low High Frequency Limit and Acquisition Mode have not been changed and the spectrometer is still in the step scan mode when the measurement is started the mirror is moved to the start position and the measurement starts Otherwise the spectrometer may switched to the rapid scan mode in order to set all relevant parameter and after wards it is switched back to the step scan mode Bruker Optik GmbH OPUS STEP 19 Time Resolved Step Scan with a Transient Recorder The status bar displays the actual operation mode of the spectrometer and the current mirror position You can interrupt or terminate a measurement by right clicking on the status bar and selecting either Stop task or Abort task If a mea surement is terminated prematurely the missing data points are added with the intensity value of the last data point After the measurement the spectrometer remains in the step scan mode The raw data are calculated using the defined FT parameter and then stored automatically in the desired data block type containing the single time slices of the time resolved measurement in chronological order and the FT parameters of measurement 20 OPUS STEP Bruker Optik GmbH Index Numerics 3D correlation 13
9. cantly because step scan mea surements are sensitive to vibrations So a longer measurement time may have a negative effect on the spectrum due to external vibrations Therefore repeat the measurement several times instead of using a high coadd count value Bruker Optik GmbH OPUS STEP 11 Time Resolved Step Scan with the internal ADC Trigger Mode Possible settings are Internal External Positive Edge and External Negative Edge The experiment can be triggered either internally or externally If you select the internal trigger mode the excitation of the sample is started synchronously with the first digitization pulse If you select an external trigger mode the digitization is performed after the specified edge of the experiment trigger is detected Trig gering can be set to occur either on the positive or negative going edge of the pulse Experiment Recovery Time If the experiment is repeated several times specify an Experiment Recovery Time to allow the sample the source or the electronics to recover between the single measurements The purpose of repeating the experiment is to improve the signal to noise ratio The recovery time depends on the sample It should be large enough to achieve identical repetitions Stabilization Delay after Stepping The Stabilization Delay after Stepping is a wait time of the system allowing the mirror to stabilize after it has moved to a new position Note Do not confuse the Stabilizatio
10. d Unused If the transient recorder is operated at its highest possible time resolution this option may be the only one accepted by the dialog In case of the PAD82B tran sient recorder board for example you set the max time resolution to 4ns and then select another option than Unused from the Second Channel drop down list the Second Channel and the Time Resolution field get a red background If you move the cursor over these fields the following error message appears This time resolution is only supported in single channel mode The reason therefore is that this board achieves its maximum speed only in the interleaved mode uti lizing both ADCs for the same channel Use for Phase Correction Normally phase correction algorithms function properly only if the resulting spectrum has exclusively positive intensities If this is not the case the DC sig nal from the detector preamplifier can be digitized in the second channel of the 18 OPUS STEP Bruker Optik GmbH Starting the Measurement PAD board As the DC signal yields a positive spectrum it can be used for cal culating the correct phase which is then used to correct the phase of the signal from the first channel Use second channel for weighting If the intensity of the excitation signal is not constant the response of the sam ple to the excitation will also vary proportionally Therefore it becomes desir able to compensate the variations This can be done by digi
11. e FT parameter defined in the standard Measurement dialog box and then stored automatically in the desired data block type Note If you have activated the Use previous option button s do not switch between the rapid scan mode and the step scan mode when performing the refer ence and the sample measurement Otherwise the absolute start position of the mirror can slightly be different 3 4 Overflow Detection during the Measurement If the signal exceeds the ADC input voltage range the following error message appears Signal too large for ADC overflow This means that the measurement signal is larger than the dynamic range of the analog to digital converter ADC This can lead to large artifacts in the spectra In this case abort the measurement Before you repeat the measurement reduce the amplification factor To do this click on the Optic tab and select a lower Sample Signal Gain value Bruker Optik GmbH OPUS STEP 7 Time Resolved Step Scan with the internal ADC 4 Time Resolved Step Scan with the internal ADC 4 1 General Information This option allows the study of fast physical processes with a time resolution up to 5usec using the standard internal analog to digital converter ADC It requires special hardware and the OPUS STEP software package We also rec ommend the OPUS 3D software package to display the results in stacked plot and contour plot views During this fast type of time resolved measurement t
12. ents can be performed either with the inter nal analog to digital converter or a transient recorder The results of a time resolved Step Scan experiment are stored in a 3D file To display or process these files the OPUS 3D software package is required Hardware Requirements Computer System The following requirements must be met to ensure an optimum operation the of OPUS STEP Software e one ISA slot for the Acquisition Processor AQP e depending on the application e g for time resolved measurements in the nanosecond domain a second ISA slot is required Note PC data stations that fulfill the above listed requirements are available directly from Bruker Spectrometer The Step Scan option is available on the following Bruker FT IR spectrometers EQUINOX 55 IFS 66 S e IFS 66v S Bruker Optik GmbH OPUS STEP Step Scan Modulation To perform step scan measurements hardware and firmware upgrades i e step scan option part number S 510 of the base configuration of the above listed spectrometers are required Note The OPUS STEP software package is included in the step scan option part number S 510 For particular applications additional options and or accessories might be nec essary For further information contact your local Bruker representative Step Scan Modulation 3 1 General Information This measurement mode is designed for photoacoustic spectroscopy PAS and other modulation demodulation experi
13. etween the following options Compute If you select this option the program automatically calculates the phase angle between the modulation signal and the detector signal Since the modulation signal is not digitized during the measurement the phase angle cannot be computed by a direct comparison of detec tor signal and modulation signal Instead it is computed from the Bruker Optik GmbH OPUS STEP 5 Step Scan Modulation assumption that the in phase component is much larger than the quadrature contribution Thus the program finds a phase rotation by an angle that maximizes the in phase component This angle q maximizing the in phase component is the demodulation angle The in phase component and the quadrature component found in this way can still be subject to further manual phase rotations by the angle 5 To do this select in the OPUS Manipulate menu the func tion Spectrum Calculator and apply the following formulae R 5 R x cos d I x sin and I o 6 R x sin d x cos 6 Note If you perform this transformation often we recommend working with a macro The macro editor allows the use of R and data blocks Use previous This option allows you to use the stored phase angle of the previous measurement Select this option when you measure a reference sam ple e g carbon black with a defined phase angle first and then use the phase angle of this reference sample for the follo
14. f interferograms measured with the specified time resolution It also determines the total time the detector will detect the signal at a given interferometer mirror position For example if you set the time resolution to 10us and define 20 timeslices a total measurement time of 200us is covered yielding 20 interferograms at 10us intervals For each timeslice a separate interferogram or spectrum is saved depending on the data blocks you have selected in the Data blocks to be saved group field on the Advanced page 16 OPUS STEP Bruker Optik GmbH Setting up Measurement Parameters Timebase Possible settings are External Linear Timescale and Compress to Log Time scale External This option allows you to apply an external signal which needs not be equidis tant in time Linear Timescale The linear timescale uses the internal clock of the transient recorder that pro duces an equidistant time raster Each resulting interferogram belongs to a time t that is multiple of the constant time resolution At t n x At with n being the running number of the interferogram Compress to Log Timescale This option also uses the internal clock of the transient recorder to produce a set of equidistant sampling points linear in time Then the sampling points are averaged along the time axis so that an equidistant time axis results Input Range Depending on the selected transient recorder the following options are possible 200
15. he entry of a positive value N gt 0 causes the initiation of the data acquisition after N timeslices have elapsed after triggering The entry of a negative value N lt 0 allows data acquisition of N timeslices before the trigger output only in case of internal triggering Experiment Recovery Time If the experiment is repeated several times specify an Experiment Recovery Time to allow the sample the source or the electronics to recover between the single measurements The purpose of repeating the experiment is to improve the signal to noise ratio The recovery time depends on the sample It should be large enough to achieve identical repetitions Stabilization Delay after Stepping This stabilization delay is the wait time after the mirror has moved to the next position and has stabilized Note Do not confuse the Stabilization Delay after Stepping with the Experiment Recovery Time Stabilization Delay after Stepping means that the experiment is delayed after a mirror step while the Experiment Recovery Time occurs before an stabilization delay begins The Stabilization Delay after Stepping must be longer than the settling time of the detector and the amplifier Using an AC coupled amplifier set this value to at least 100ms Second Channel The Second Channel drop down list contains the following options Unused Use for Phase Correction Use for Weighting Use for Weighting discard if lt Threshold Discard Experiment if lt Threshol
16. he interferogram is acquired in step scan mode by repeating the following procedure at every mirror position As soon as the interferometer mirror has reached a new position the mirror settles for a certain time specified by the parameter Stabilization delay after stepping Then x experiments are initiated and averaged with x being the Repetition Coadd Count Between the experiments the sample is allowed to recover for an Experiments recovery time specified in milliseconds During the experiment the sample is excited e g flash of light or a quick field change and the detector response to the perturbation is scanned in N timeslices with N being the Number of timeslices i e the changing ADC signal is digitized N times at equidistant time intervals specified by the Time resolution At the end of the measurement the data are sorted in N interferograms Depending on the data blocks you have selected in the group field Data blocks to be saved on the Advanced page either the interferograms or the spectra or both will be saved in the resulting 3D file During the measurement the sample will be excited repeatedly NPT x Repeti tion Coadd Count times with NPT being the number of data points of the inter ferogram Thus it is necessary that the sample reacts reversibly to the excitation of the experiment and does not degrade 4 2 Setting up the internal ADC Before performing a time resolved measurement with the internal ADC you must set up th
17. irst zero crossing of J entering the correct modulation amplitude is of crucial importance Setting the modulation amplitude to 1 0 fringe corresponds to a zero crossing of J at 9638cm while a modulation amplitude value s 2 fringes causes a zero crossing at 4819cm etc The highest signal response however is observed at the largest possible amplitude Therefore the optimal modulation amplitude is a compromise choose the largest possible amplitude that will keep the spectral region of interest above the first zero crossing of Jj 4 OPUS STEP Bruker Optik GmbH Setting up Measurement Parameters Amplitude Modulation In addition to the phase modulation PM a modulation signal for the amplitude modulation AM can be created that is accessed as a TTL voltage at the Aux out BNC port of the I O cable The amplitude modulation frequency is selected in the same way as the phase modulation frequency as described above The drop down list Modulation Fre quency contains all possible modulation frequencies as integer values Note that only discrete modulation frequencies are available So if you enter a value instead of selecting an option the entered value is corrected automatically by the TC 20 controller Note The higher frequency value fp of the two frequencies must always be an integral multiple P fy f of the lower frequency f Since both frequencies derive from the same quartz oscillator the phase length of both sig
18. is device To do this select in the OPUS Measure menu the Optic Setup and Service function The Optic Setup and Service dialog box opens Click on the Devices Options tab Activate the Transient Recorder check box figure 2 and click on the Setup button OPUS STEP Bruker Optik GmbH Setting up the internal ADC Optic Setup and Service a xj Optical Bench Devices Options Interferometer AQP Export Options Service Optic Communication M Source IV Beamsplitter Optical Filter IV Aperture Iris Aperture J7 Polarizer M Channel I Sample Changer V Detector IV Preamplifier Gain IV Velocity IV High Pass Filter IV Low Pass Filter Setup Setup Setup Setup Setup Setup Setup Setup Setup Setup Pebble Setup IV Use Login Operator Name I Automatic Accessory Recognition I Gain Switch Gain I Multiplexed Data IV Wait for Devices Ready J PLL Laser Multiply User Signals 7 AQP with Digital Filters IV Ext Synchronisation Sonde Setup I Mapping Device Setup IV Transient Recorder Setup T Imaging Device Setup Setup Result Spectrum Save Settings Cancel Help Figure 2 Optic Setup and Service Dialog Box Setting up the internal ADC The Device Options dialog box figure 3 opens Make sure whether an entry containing the string ADC already exists in the list If so the internal ADC option is already set up Otherwise click on the Add New Item button and enter
19. k on the Multiple Channel option button and check the desired input channels 6 OPUS STEP Bruker Optik GmbH Starting the Measurement During the measurement the signals of these channels are collected subse quently For each channel a separate result file is generated If you click on the Single Channel option button only one signal is collected from the standard input jack of the associated detector 3 3 Starting the Measurement To start the measurement click on the Basic tab and then on the Start Step Scan Modulation Measurement button If the parameters Resolution Phase Resolution Wanted Low High Frequency Limit and Acquisition Mode have not been changed and the spectrometer is still in the step scan mode when the measurement is started the mirror is moved to the start position and the measurement starts Otherwise the spectrometer may switched to the rapid scan mode in order to set all relevant parameter and after wards it is switched back to the step scan mode The status bar displays the actual operation mode of the spectrometer and the current mirror position You can interrupt or terminate a measurement by right clicking on the status bar and selecting either Stop task or Abort task If a mea surement is terminated prematurely the missing data points are added with the intensity value of the last data point After the measurement the spectrometer remains in the step scan mode The raw data are calculated using th
20. mV 500 mV 1V 0 400mV 0 2V Upon specifying the Input Range bear into mind that the maximum signal fills the dynamic range of the ADC of the transient recorder in the best possible way Repetition Coadd Count This value represents the number of data acquisitions to be performed at each mirror position The purpose of coaddition is noise reduction By increasing this value the signal to noise ratio can be improved to a certain degree We recom mend a value between 10 and 50 A higher value e g more than 100 does not improve the signal to noise ratio significantly because step scan measurements are sensitive to vibrations So a longer measurement time may have a negative effect on the spectrum due to external vibrations Therefore repeat the measure ment several times instead of using a high coadd count value Trigger Mode Possible settings are Internal External Positive Edge and External Negative Edge The experiment can be triggered either internally or externally If you select the internal trigger mode the excitation of the sample is started synchronously with the first digitization pulse If you select an external trigger mode the digitization is performed after the specified edge of the experiment trigger is detected Trig gering can be set to occur either on the positive or negative going edge of the pulse Bruker Optik GmbH OPUS STEP 17 Time Resolved Step Scan with a Transient Recorder Pre Post Trigger T
21. ments First the IR beam is modulated at one or more discrete frequencies Then the detector signal is demodulated at the same frequency so that the intensity at a given frequency and phase angle relative to the modulation signal can be measured and quickly determined for every interferometer mirror position There are two kinds of modulation amplitude modulation e g by chopping the IR beam or by manipulating the sample itself periodically such as stretching or photoelastic modulating and phase modulation i e periodic vibration of the interferogram mirror about each set position The demodulation is performed either by an external lock in amplifier LIA or if the DSP option is available by an internal digital signal processor DSP 3 2 Setting up Measurement Parameters Select in the OPUS Measure menu the Step Scan Modulation function The Step Scan Modulation dialog box opens Basically this dialog box is identical to the Measurement dialog box described in the OPUS Reference Manual except for the Step Scan Modulation page Click on the Step Scan Modulation tab The dialog window shown in figure 1 opens It allows you to define the necessary parameters to perform a step scan modulation measurement Note Before starting a measurement ensure that all parameters are set correctly For detailed information on the measurement parameters of the other dialog win dows refer to the OPUS Reference Manual 2 OPUS STEP Bruker Op
22. n Delay after Stepping and the Experiment Recovery Time The Stabilization Delay after Stepping runs only one time after each mirror step while the Experiment Recovery Time runs n times with n being the number of co additions Note that the Stabilization Delay after Stepping must be longer than the settling time of the detector and the amplifier Using an AC coupled amplifier set this value to at least 100ms 4 4 Starting the Measurement To start the measurement click on the Basic tab and then on the Start Step Scan Time Resolved Measurement button If the parameters Resolution Phase Resolution Wanted Low High Frequency Limit and Acquisition Mode have not been changed and the spectrometer is still in the step scan mode when the measurement is started the mirror is moved to the start position and the measurement starts Otherwise the spectrometer may switched to the rapid scan mode in order to set all relevant parameter and after wards it is switched back to the step scan mode The status bar displays the actual operation mode of the spectrometer and the current mirror position You can interrupt or terminate a measurement by right clicking on the status bar and selecting either Stop task or Abort task If a mea surement is terminated prematurely the missing data points are added with the intensity value of the last data point After the measurement the spectrometer remains in the step scan mode 12 OPUS STEP Bruker Optik GmbH
23. nals does not change during the measurement DSP Demodulation The option DSP Demodulation is only available if an internal phase modulation PM and amplitude modulation AM can be performed using an internal digi tal signal processor DSP this means that no lock in amplifier LIA is required This kind of demodulation allows the measurement signal demodula tion of the PM component as well as the AM component For each measurement channel two single channel data blocks are generated as the result of a PM demodulation These data blocks are marked with R and J R represents the component of the detector signal that is in phase with the mod ulation signal in phase while represents the component of the detector signal which is shifted 90 degrees from the modulation signal quadrature If both the the phase modulation and the amplitude modulation are performed during the measurement the amplitude demodulation also generates a R and data block representing the in phase and quadrature component of the AM signal Demodulating two frequencies the system acts like two lock in amplifiers con nected in series first the component with the higher frequency fp is demodu lated then the component with the lower frequency fio Phase Demodulation Angle Amplitude Demodulation Angle The OPUS STEP software package allows you to define the phase demodula tion angle as well as the amplitude demodulation angle To do this you can choose b
24. ns OPUS supports the following following transient recorders 14 OPUS STEP Bruker Optik GmbH Setting up Measurement Parameters 1 2 3 4 5 6 Note The transient recorders 1 to 3 are equipped with the fast 8 bit board and the transient recorders 4 to 6 have a dynamic range of 12 bits PAD82A PAD82B PAD82 PAD1232a PAD1232b PAD1232c If no transient recorder is connected to your spectrometer make sure that the Transient Recorder check box is not activated Devices Options E Transient Recorder Format Figure 6 Devices Options Dialog Box Selecting the Transient Recorder 5 3 He eae nnn M2 PADE2B M3 PAD82 M4 PAD1232a MS PAD1232b 6 PAD 1232c Setting up Measurement Parameters Item UP Item DOWN Edit Item Add New ltem Delete Item Restore Factory Defaults Select the Time Resolved Step Scan function in the Measure menu The Step Scan Time Resolved Measurement dialog box opens Basically this dialog box is identical to the Measurement dialog box described in the OPUS Reference Manual except for the Recorder Setup page Click on the Recorder Setup tab The dialog window shown in figure 7 opens It allows you to define the necessary parameters to perform a time resolved step scan measurement Note Before starting a measurement ensure that all parameters are set correctly For detailed information on the measurement parameters of the other dialog win
25. ore performing a time resolved measurement with a transient recorder you must set up the transient recorder To do this select in the OPUS Measure menu the Optic Setup and Service function The Optic Setup and Service dialog box opens Click on the Devices Options tab Activate the Transient Recorder check box figure 5 and click on the Setup button Optic Setup and Service x Optical Bench Devices Options Interferometer AQP Export Options Service Optic Communication IV Source Setup M Use Login Operator Name IV Beamsplitter Setup I Automatic Accessory Recognition J Optical Filter Setup I Gain Switch Gain IV Aperture Setup J Multiplexed Data Iris Aperture IV Wait for Devices Ready J Polarizer P PLL Laser Multiply IV Channel I User Signals T Sample Changer Setup 7 AGP with Digital Filters IV Detector Setup IV Ext Synchronisation Sonde Setup IV Preamplifier Gain Setup I Mapping Device setup IV Velocity Setup IV Transient Recorder Setup IV High Pass Filter Setup J Imaging Device Setup IV Low Pass Filter Setup Setup Result Spectrum Save Settings Cancel Help Figure 5 Optic Setup and Service Dialog Box Setting up the Transient Recorder The Device Options dialog box figure 6 opens The available transient record ers that are displayed in the list depend on your spectrometer Select the tran sient recorder that is connected to your spectrometer and uncheck all other optio
26. rs of the other dialog win dows refer to the OPUS Reference Manual Step Scan Time Resolved Measurement x BH Basic Recorder Setup Advanced IBN Optic Acquisition FT Check Signal Device MEME RA r Sampling Time Resolution 5 us Number of Timeslices fro Timebase Linear Timescale Input Range ao Repetition Coadd Count fi Experiment Trigger Mode Internal Experiment recovery time fo ms Stabilization delay after stepping fao ms Exit Cancel Help Figure 4 Step Scan Time Resolved Measurement Dialog Box Recorder Setup Device Select the option Internal ADC from the Device drop down list Note that once you have selected this option the dialog window only displays those parameters being relevant for the internal ADC option Note This list contains all devices that are listed and checked in the Devices Option dialog window figure 3 10 OPUS STEP Bruker Optik GmbH Setting up Measurement Parameters Time Resolution In case of internal triggering the Time Resolution is the time interval between detector output digitizations and consequently also the time interval between subsequent timeslices or spectra The maximum time resolution is 5us Do not enter a larger time resolution value also in case of external triggering Number of Timeslices This value represents the total number of interferograms measured with the specified time resolu
27. s acquired in step scan mode by repeating the following procedure at every mirror position As soon as the interferometer mirror has reached a new position the mirror settles for a certain time specified by the parameter Stabilization delay after stepping Then x experiments are initiated and averaged with x being the Repetition Coadd Count Between the experiments the sample is allowed to recover for an Experiments recovery time specified in milliseconds During the experiment the sample is excited e g flash of light or a quick field change and the detector response to the perturbation is scanned in N time slices with N being the Number of timeslices i e the changing ADC signal is digitized N Bruker Optik GmbH OPUS STEP 13 Time Resolved Step Scan with a Transient Recorder times at equidistant time intervals specified by the Time resolution At the end of the measurement the data are sorted in N interferograms Depending on the data blocks you have selected in the group field Data blocks to be saved on the Advanced page either the interferograms or the spectra or both will be saved in the resulting 3D file During the measurement the sample will be excited repeatedly NPT x Repeti tion Coadd Count times with NPT being the number of data points of the inter ferogram Thus it is necessary that the sample reacts reversibly to the excitation of the experiment and does not degrade 5 2 Setting up the Transient Recorder Bef
28. the time constant of the AC coupling link typically gt 100 milliseconds are sufficient Number of Coadditions This parameter has different meanings depending on whether you use an exter nal lock in amplifier LIA or an internal digital signal processor DSP External LIA After the stabilization delay has elapsed the output signal of the lock in amplifier is digitized at 10 microseconds inter vals according to the value entered in the field Number of Coaddi tions Afterward the values are summed and averaged For example 2000 coadditions correspond to a digitization time of 20 millisec onds Bruker Optik GmbH OPUS STEP 3 Step Scan Modulation Internal DSP After the stabilization delay has elapsed measure ments are performed periodically according to the lowest modulation frequency and the value entered in the field Number of Coadditions If for example the phase modulation frequency is 414 Hz and the amplitude modulation frequency 17 Hz the measurement intervals are N multiples of the period length of the 17 Hz signal 1 17 s with N being the Number of Coadditions The period of the lowest modulation frequency is used as a minimum value Phase Modulation If you activate this check box the internal phase modulation is performed auto matically The interferometer mirror oscillates about the step position with the specified modulation frequency and the specified modulation amplitude Modulation Frequency The
29. tik GmbH Setting up Measurement Parameters Step Scan Modulation j i x H Basic Step Scan Modulation Advanced EY Optic Acquistion FT Check Signal Stabilization Delay 10 msec Number of Coadditions 10 Y Amplitude Modulation J Phase Modulation Modulation Frequency 418 y Hz Modulation Frequency 203 y Hz Modulation Amplitude 1 Fringes v DSP Demodulation Phase Demodulation Angle r Amplitude Demodulation Angle C Compute Compute C Use Previous C Use Previous Angle OR C Angle g C Single Channel Multiple Channels v do gt mg gt gt 1 Exit Cancel Help Figure 1 Step Scan Modulation Dialog Box Setting up the Measurement Parameters Stabilization Delay In the Step Scan mode the interferometer mirror moves in a stepwise manner to each position After the interferometer mirror has reached a position it requires a settling time to stabilize at that position Then the system waits for a user defined period the Stabilization Delay before it starts the data acquisition The Stabilization Delay is an additional time in milliseconds for the mirror to fur ther stabilize after a step Note Using an external lock in amplifier LIA the stabilization delay should be set to at least six times of the lock in time constant When working with AC cou pled detectors the stabilization delay should be larger than
30. tion It also determines the total time the detector will detect the signal at a given interferometer mirror position For example if you set the time resolution to 10us and define 20 timeslices a total measurement time of 200us is covered yielding 20 interferograms at 10us intervals For each timeslice a separate interferogram or spectrum is saved depending on the data blocks you have selected in the Data blocks to be saved group field on the Advanced page Timebase Possible settings are Linear Timescale and External Linear Timescale The linear timescale uses an internal clock that produces an equidistant time raster Each resulting interferogram belongs to a time that is multiple of the constant time resolution At t n x At with n being the running number of the interferogram External This option allows you to apply an external signal which needs not be equidis tant in time Input Range In case of measurements with the internal ADC the only possible setting is 10 Volt A signal having this voltage will fill the dynamic range of the ADC Repetition Coadd Count This value represents the number of data acquisitions to be performed at each mirror position The purpose of coaddition is noise reduction By increasing this value the signal to noise ratio can be improved to a certain degree We recom mend a value between 10 and 50 Note that a higher value e g more than 100 does not improve the signal to noise ratio signifi
31. tizing the excitation signal in the second channel of the transient recorder and computing a correc tion factor using this digitized signal more precisely using only those parts of the excitation signal which are larger than 80 of its average signal Then the correction factor is used to correct the signal of the first channel Use for weighting discard if lt Threshold This option is identical to the option Use second channel for weighting with one exception in addition to the Use second channel for weighting option it is checked whether the excitation signal is smaller than the threshold If this is the case the data of the current experiment is discarded This is signaled by a beep of 1000Hz The threshold value range is between 0 0 no threshold and 1 0 maximum threshold The value 1 0 corresponds to full positive scale i e if the Second Channel Input Range is set to 500 mV for example it corre sponds to 500mV which in case of a 8 bit boards is in accordance with 128 ADC counts Useful threshold values must be smaller than 1 0 Discard Experiment if lt Threshold This option does not normalize the signal of the first channel but discards the data of the current experiment if the signal of the second channel is smaller than the threshold and repeats the measurement This option is useful for cases in which the intensity of the excitation signal is quite reproducible but may some times fail completely e g if a fl
32. wing measure ments e g phase resolved DSP experiment The phase angle remains stored in the acquisition processor until it is overwritten by a new one that is calculated with the Compute option Note Since this program can only recognize one phase angle this option cannot be used for measurements performed simultaneously with multiple channels because all channels use the same phase angle Angle This option allows you to enter the desired phase angle manually as a numerical value in degrees Select this option if a phase angle has been determined from the instrument parameters of previous mea surements Note Since this program can only recognize one phase angle this option cannot be used for measurements performed simultaneously with multiple channels because all channels use the same phase angle Single Channel Multiple Channels The OPUS STEP software package allows you to choose between the options Single Channel and Multiple Channels If you perform measurements with a lock in amplifier the IR beam is coupled to that detector which is defined in the standard measurement dialog box With out changing the mirror position of the detector up to seven electrical input channels for the detector multiplexer board can be selected i e up to seven sig nals can be collected at the same time This option is useful for collecting the in phase and quadrature output signals of one or more external lock in amplifiers To do this clic
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