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1. WinCamD Series TaperCamD Series WinCamD Baseline Setting DataRay Confidential Applies to All current WinCamD series products Software version 7 1H10 amp higher for the current iteration Camera 1 eha 771 4 om Poel l aor Jbz T Clip a 13 5 r Clip b 50 0 Maj4ISO 2745 7 um Min 30O 1302 6 um ELP 179 5 deg _Ellip Orient rosshair 79 5 deg _Xc 63 3 um Ye 266 0 um E Relative Power E0 Full Range 2 D Trigger eff delay 0000 me imager Gain 10 7 4 i Espasure time 19 73 ma Auty i _ADC Peak Image zoom 1364 3 um 837 8 um 2Wua 13 5 Scale T000 mmfdie Peak 774X 0 19 Scale F000 umpdiw Pesk bii A 11 Summary This Technical Note describes the four baseline setting modes of DataRay WinCamD series software Note Competitor assertions that theirs is the only beam profiler algorithm that sets the baseline in the center of the noise and does not truncate electronic noise below zero are simply incorrect e Auto baseline This default real time mode present in various iterations since the 90 s handles most beams On the laser pointer in the example above the un averaged diameter readings in a typical lab environment are stable to 0 05 rms 0 25 pk to pk a direct consequence of the auto baseline algorithm stability e Baseline Lock Use with beams which overfill th2. e sensor Locks auto baseline at its current value e Background Subtraction Use if there is substantial optical background to deal with e HyperCal Real time subtraction of electronic shading Important in Use equivalent slit mode amp with comet tailing Real time frame by frame baseline setting amp the background subtraction option have been features of DataRay software since the nineties what we simply call doing it properly Auto baseline has recently been further refined HyperCal is a new feature Technical Background For a perfect Gaussian the 1 e beam diameter error is nearly twice the baseline setting error e g a 0 1 error in the baseline setting results in a 0 18 error in the measured beam diameter There are no perfect sensors and no perfect electronics Real world cameras must set a baseline for analysis that corresponds to zero irradiance Negative irradiance does not exist but electronic noise and offsets at the input to the ADC Analog to Digital Converter can drive signal above and below the zero irradiance equivalent input voltage ADC s are unipolar so zero irradiance is always a non zero voltage at the ADC input servoed to around 2 of the ADC range in DataRay systems with ADC s external to the sensor Because background amp noise can vary over time real time baseline setting is important Historically noise offsets and offset drifts were higher than with current generation sensors and electro
3. m is smoothed by a 32 level wide equal weight smoothing function 0 05 of the total ADC range Without this smoothing such a histogram is too peaky to be useful The software analyzes the histogram to determine the first peak above zero in the histogram lbaseline typically around the 1300 level the 2 level of the ADC range an Level Create the array to be processed as an image limage X Y Iraw X Y Ibaseline Level Is the default mode of operation and works really well for the vast majority of beams those roughly centered in the Capture Block but which do not overflow the Capture Block Sy a 2Wub i 50 0 2202 1 um 3 ARA e a ee 3 Real time No accuracy versus ease of use tradeoff required Requires no warm up time and no user intervention Works with Auto exposure amp Auto gain as well as at fixed Exposure amp or Imager Gain n Sesa M00 mfd Is simply confirmed by observing the profile baseline in log 40dB mode Residual noise is typically below 0 1 May be further improved by simply using the Average function Baseline Lock for large beams which overfill the camera Set once User Manual Sec 3 4 p 56 Bl a b Philosophically the aim is to establish and subtract the ADC level corresponding to zero irradiance for beams which overfill the camera negating histogram peak finding in the default auto baseline function The padlock style Lock and Unlock but
4. nics and processing power was lower One approach was to spend time at the start of a measurement session allowing everything to stabilize taking and processing a reference frame in the dark and performing a live image correction based on subtraction of this processed reference data This was then applied to all subsequent beam images in the session until a recalibration was deemed appropriate DataRay considers now this approach no longer necessary or appropriate WinCamD Baseline Setting Ver 1202a Page 1 of 3 DataRay Inc Bella Vista CA 203 210 5065 www dataray com Implementation Descriptions Real time auto baseline No user intervention required a b c d e This approach waa ie Philosophically the aim is to establish and subtract the ADC level corresponding to zero irradiance This requires us to find the peak in the levels near zero irradiance outside the beam area y If the Capture Block is H x V pixels the software inscribes a circle of diameter H or V N D whichever is smaller Pixels outside this circle but within the Capture Block constitute the data to be processed for baseline setting E g For a square capture region this selects the corners of the image the hatched areas above The software creates an internal histogram of ADC level versus number of pixels at this level It also performs a 32 frame rolling average of the histogram Because a 16 bit ADC word has 65 536 levels the histogra
5. on the difference image e Press the bracket button to turn it off WinCamD Baseline Setting Ver 1202a Page 2 of 3 DataRay Inc Bella Vista CA 203 210 5065 www dataray com HyperCal for occasions where shading in the electrical offset need to be rejected Set once EA User Manual Sec 3 4 p 57 a Philosophically the aim is to subtract any unwanted electronic offset which is non uniform across the sensor Tends to matter most when Use Equivalent Slit is engaged when baseline tilt always present but normally negligible for practical purposes can become significant in the integrated line profile Can be engaged at any time for any reason at exposures gt 0 4 ms b HyperCal alternately takes exposures at the lowest possible exposure and at the auto or set exposure and differences the frames Auto baseline operates on the difference image HyperCal therefore completely removes electronic offsets at the ADC that do not result from the presence of an image c Press the button again to turn it off Log profile displays no averaging n a et a a aad ia SS ST E Without HyperCal With HyperCal 0 3 noise baseline tilt Noise lt 0 1 amp flat baseline WinCamD Baseline Setting Ver 1202a Page 3 of 3 DataRay Inc Bella Vista CA 203 210 5065 www dataray com
6. tons allow you to Lock the baseline at the current level set by the auto baseline function above This allows the measurement of beams which overfill the sensor and are therefore too large to allow the determination of a good zero level while the beam is on the camera With the beam on the camera uncheck auto exposure Then block the beam and click on the Lock padlock style button Then unblock the beam The zero level from which clip levels are determined will be now be based upon the level determined while the beam was blocked Obviously if beam wings are absent second moment 40 widths calculated for such a beam are invalid To disable this feature click on the Unlock padlock button Background Subtraction for beams on top of an optical background which needs to be rejected Set once H User Manual Sec 3 4 p 57 a Philosophically the aim is to subtract an unwanted optical background Prompt x b Right click on the Exposure time box amp disable auto exposure Click OK If appropriate set Average 20 especially if the background to be subtracted Block beam and press OK IS noisy c Click the button to initiate background subtraction The box shown right will appear Block the beam allow any selected averaging to complete and then Cancel click OK The captured background optical and electrical is subtracted i me from subsequent images If Average is still engaged subtraction will be gradual d Auto baseline operates
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