7. Horiba / Sofie Laser Interferometer Teardown
All datasheets etc are at the bottom of this page.
A number of these interesting assemblies came up on eBay UK. Initially I planned on inspecting my LIBS target ablation pit (the LHC Project beam focus goal is 50µm or better) using a CCD camera. I bid on and won two of these these solely to get the lenses to experiment with. When they arrived I Googled and found out more about them:
http://www.horiba.com/cn/scientific/products/process-equipment/endpoint-detection/details/lem-502
'LEM - Imaging Interferometric Camera
The LEM consists of an interferometric camera with a simple analog output of signal intensity. The compact head design is ideal for easy and rapid installation on chamber top windows. It integrates either a 670nm or 905nm laser source, a signal detector and a CCD camera. The CCD camera produces a real-time digital image of the wafer surface allowing the laser beam to be positioned accurately using a manual stage. The LEM includes illumination intensity control to optimize the visibility of the laser spot on different samples depending on their reflectivity. This significantly enhances image quality.'
The link below has more info on this and similar systems:
http://www.horiba.com/semiconductor/products/measuring-object/etching-end-point/details/real-time-interferometric-process-monitor-lem-ct-670-g50-2887
The information sheet 'Sofie interferometric camera.pdf' (see bottom) includes a photo of an IC chip structure viewed by its CCD camera and suggests at 150mm distance from its target, its built in laser has a visible (670nm) 20µm diameter spot which would be a useful reference. At that distance it has a magnification of 120x which translates 50µm to 6mm which is tiny, but if the camera worked and resolution was high enough, I might be able to use the complete assembly to measure the pit.
Afterwards I found a paper [L6] with the following words on page 4: 'Laser crater profiles were measured with white light interferometer microscope', so this idea was pretty close.
Below, the Horiba ISA Jobin Yvon Sofie Instruments interferometric IC wafer inspection camera and its 50mm lens from an earlier auction:
Below, the two different laser interferometers I bought. The one on the left was made by Horiba and includes the manual X-Y stage described in Sofie interferometric camera.pdf. The one on the right was made by Sofie Instruments, and only includes the mounting base plate.
The first thing that puzzled me was the BNC connector inside the large round knurled knob on the side of the assy. Unscrewing it, I found an 8mm diameter photodiode mounted on a pcb with a BNC connector, looking remarkably similar to the 7.98mm dia 190-1100nm Hamamatsu S2281-04 (datasheet below).
Next step was to identify the pinout of the 7-way circular connector. I emailed Horiba but I'm not surprised they didn't bother to reply. No matter, I reverse engineered it and can reveal everything I found here, their loss. The connector has no part number but is marked 'L] Made in W.Germany'. This was enough for me to identify it as a Binder with mating part number 680 09 0326 00 07, on eBay Uk for $4:
Opening the Horiba, I found the big connector soldered to a pcb on which voltages had been conveniently marked, but it wasn't immediately obvious what all of the pins were for and the compact design looked difficult to disassemble, without which it was impossible to see any part numbers on the lamp or CCD. I was concerned I might disturb the optical layout, but soon realised it was of robust construction and once the lid was off, dust would get in regardless. The laser part is marked FP-67/4XF-GL35-GD11,5-SEL, but nothing came up on the web. I guessed '5' meant 5V.
Having the Sofie variant as well proved very fortunate as when I opened it I found it was a different design and much easier to disassemble. Again the CCD was inaccessible, but on the back it said VCM3250/00. Google revealed this is a Philips part and even brought up a datasheet, but at 75MB because remarkably it includes schematics, it's too big to include here, so instead here is a link to it:
I now had a spec for the CCD: 1/2" 400-1000nm 512Hx582V CCIR 625 lines UK PAL 50Hz. Once I had the pcb out, I was able to trace all of the connector pins, which also clearly matched the Horiba assembly, and in turn meant I had a spec for that too.
Below left, the Horiba inside Below right, the Sofie inside:
Not all of the 7-way connector signal names are marked on the pcbs so I dismantled the Sofie, see below. Apart from the Horiba having two lid safety cutout micro switches (one to disable the laser, the other to disable the lamp) and a few minor differences, the two assemblies are pretty much the same.
The first step was to remove the lens, the inside section of which differs for each unit. Both have extension tubes inside, but the Sofie also has another lens on the far end. Both extension tubes are secured by means of an allen screw accessible through a hole in the side of the box. The lens extension lifts out once the three screws holding a bezel to the case are removed:
Once the lenses are out it is possible to extract the remaining sub assemblies, which consist of the switch and connector block attached to a pcb, a corner block containing the fan and lamp assembly, and the main optical assembly which also has the CCD at its rear end. The Sofie must have been an older design because the CCD has three circuit boards (below right) laden with components on both sides and is so large the optical assembly is been sandwiched between them. They were crudely secured by hot melt glue to the thin black cardboard sheets that block light from entering the optics above and below. By contrast, the Horiba CCD is a single compact board mounted at the rear of the optical path. Once the cardboard is removed it is possible to see (below left) the outline of the optical assembly which ties
up perfectly with the centre top diagram in Sofie interferometric camera.pdf.
Below left and centre, the Sofie connector pcb & laser with heatsink: Below right, close up on pcb:
Once dismantled I was able to trace pcb tracking and use an ohmmeter to check where the connector wires went. Below are my logbook connector and wiring observations and notes for both assemblies.
Below left, the Horiba wiring Below right, the Sofie wiring
I found the cameras and fan run off +12V, the Sofie laser runs off -12V (but the Horiba laser runs off +5V), and the lamps run off +5V.
The only thing left to identify was the lamp wattage. I was reluctant to unscrew it as it had been sealed in place, but there was no alternative and once I had gained confidence from stripping it out of the Sofie, I did the same on the Horiba:
They both have similar OSRAM 6V 10W lamps running off 5V, taking ~1.3A:
Horiba = Osram 644105: 6V 10W 110 Lumens 4000 hour G4 9.50 [RS Denmark]
Sofie = Osram 64225 6V 10W, datasheet here:
http://pdf1.alldatasheet.com/datasheet-pdf/view/124658/OSRAM/64225.html
Later when I discovered the CCDs were both very dim, I replaced the 10W lamp with 20W one, but it made little difference. Yes, I did first measure the luminous intensity of both lamps.
When the lamp lit again it was a simple matter to realign the screws for best image.
Below centre, top lamp is original identifiable OSRAM 10W part, bottom one is unmarked Chinese 20W:
Both lasers are very diminished, but given they are red, this means they had to be the 670nm variant specified in the Sofie brochure, and I confirmed this on the Stellarnet spectrometer.
Now I had the connector pinout, I made a cable with the mating 7-way connector to connect power to the units. The video output is just a conventional 75 Ohm BNC, for which I already had a cable. I hooked it up to my analogue video capture dongle and used its Multiviewer software to display the camera signals.
The inner ring of the lens is the iris, fully CW = fully open. The outer ring of the lens is the focus, fully CCW = finest focus. With a target at a distance of about 13", the external lens iris fully open and focus set to finest, its field of view is 6mm. With its 512Hx582W CCD, 6mm/512 = 0.0117mm/pixel. and 0.0117mm/25.4=0.236"/512=0.46µm resolution, confirming I should easily be able to view a 20µm ablation pit.
I found everything worked on both units except the Sofie CCD which powered up with a static image that responded to light levels and no more. The Horiba CCD actually worked, but was so insensitive I could only display a target if I illuminated it with a very bright light. The internal 10W lamps don't seem powerful enough.
I decided to replace the dead Sofie CCD with a modern equivalent and bought a supposedly high sensitivity Sony HAD pcb camera '0.03lux 700TVL PAL 0.3in CCD' from eBay China for a mere $10.
It proved to be quite easy to tease it into the assembly, but was just as dim as the Horiba CCD.
Above, the 3 pcb Sofie CCD.
Below left and centre, the replacement Chinese eBay CCD: Below right the new CCD vs old:
The lens wasn't needed so I sliced off its metal retaining barrel to fit in the CCD recess. A brass leg from a UK mains plug acts as a crude spacer to raise the CCD off the floor of the box to the correct height for the optical path.
Above left new CCD barrel too long Above right barrel chopped, fits
Whilst dismantling the old CCD, I found a 0.5" diameter 600nm centre, 40nm wide bandpass filter recessed within the optical assembly in the path immediately before the CCD.
Below inset the filter, and checking its function using the Stellarnet Black Comet SR spectrometer.
Right:
(click for bigger view)
Top spectrograph shows side of filter facing target reflects the 670nm laser peak (and the lamp) to the target.
Bottom spectrograph shows the side of the filter next to the CCD only passes 580-620nm to the CCD.
Whilst aligning the new CCD I tried it both with and without this filter, but leaving it out didn't improve CCD brightness, so I left it in as before.
Once the new CCD was in place, I ran the same tests as before, using 1/16" spaced lines running along the centre of a ruler as a target, see below. The 10W internal lamp appears as a disc of light on the target with the laser spot in the middle. The magnification is there, but the focus is dreadful.
Above, target ruler lines are 1/16" (1.5875mm) apart
Below, a xenon torch provides a little more light
The image was brighter, but still not bright enough for practical use, and focus is atrocious.
The final mystery was the small adjustment pot between the video and supply connectors on the front of the assembly. Here the CCD datasheet came in handy as its schematic suggested it was for gamma adjustment. I marked its position and rotated it - sure enough, the brightness contrast changed.
Having gone as far as I can to utilise the assemblies that seemed so promising from their sales brochures but upon investigation fall far short of being practical, I am still puzzled whether they started out with such poor intensity in the first place, or if they really have degraded so much after time. I would like to think it is the latter.
If they had worked as I hoped I would have put up with the impractical size of the assemblies. As it is, I may return to my original plan, which was to simply use their lenses, but I can also take advantage of their extension tubes to achieve the high magnification I require. The exercise was not a loss - I now know how much distance is involved in achieving this.
A future experiment still awaits, should I acquire a high power macro light or microscope illuminator. Watch this space...
Note - If you can't see the pdfs below:
Sofie interferometric camera.pdf is brochure located here:
https://www.horiba.com/fileadmin/uploads/Scientific/Documents/TFilm/lem_camera_series-lr.pdf
Hamamatsu S2281-04 PD datasheet is located here:
https://www.hamamatsu.com/resources/pdf/ssd/s2281_series_kspd1044e.pdf
P4 bottom below came from the following paper, located here:
https://arxiv.org/ftp/arxiv/papers/1308/1308.3051.pdf
Laser Beam Profile Influence on LIBS Analytical Capabilities: Single vs. Multimode Beam,
V.Ledneva, S.Pershina, A.Bunkina
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