6. Detectors & Visualisers
This section covers various optical detectors used on the LHC project, and visualisers that convert invisible wavelengths to visible for those detectors, and for general visual detection,
DETECTORS
1. Cameras
2. Lenses
3. LaserCam
4. Pyroelectric Sensors
5. Fast Photodiodes
6. Avalanche Photodiodes
7. Transimpedance Amplifier
8. Position Monitor
9. Segmented Photodiodes
10. PhotoMultiplier Tubes
11. Vacuum Phototubes
VISUALISERS
1. IR to VIS Converters
2. UV to VIS Converters
3. Diffusers
4. Laser Interferometer
5. Shear Plate Interferometer
6. UV/IR Electro-Optic Imager
MRD500 fast photodiode
1. DETECTORS
1. CAMERAS
Cohu 4815 2/3" monochrome CCD camera
Chugai Boyeki YC-22 1/2" 24V 60Hz colour camera + lens
Sony XC-75 1/2" monochrome CCD camera
These cameras measure beam profile, target ablation and target ablation crater respectively.
Two were chosen for their large 1/2" sensors, useful for measuring laser beam characteristics.
Of all of the cameras recommended by Ophir's laser profiler camera selection guide, the Cohu 4812 is the least expensive and occasionally comes up on eBay. The 4815 is the same model, but comes with an ac adaptor providing its 12V (ac or dc) supply. In particular, Ophir advises against using Pulnix TM6, TM7 cameras because they exhibit ghosting. It also advises against the Sony XC-77 and it is likely the
XC-75 has similar issues so it will not be used for profiling.
The XC-75 has an external trigger input that can work up to 1/10,000 second exposure and will be used to capture plasma generation, as well as measurement of crater quality and diameter, assisted by a precision ruler.
The YC-22 is for experimental use and will also be used to capture oscilloscope traces, accompanied by the excellent customisable Screen Calipers app which will also be used for crater measurement:
http://www.iconico.com/caliper
2. LENSES
a. CCD CAMERA LENS
The Cohu 4815 will be used to measure laser beam profile without a lens. The YC-22 comes with an integrated lens, but the XC-75 will need a C-mount lens, commonly found on 16mm movie cameras, closed-circuit television cameras, and trinocular microscope phototubes. C-mount lenses provide a male thread which mates with a female thread on the camera. The thread is nominally 1.000" / 25.4mm in diameter, with 32 threads per inch, designated as '1-32 UN 2A' in the ANSI B1.1 standard for unified screw threads. The C-mount flange focal distance is 17.526mm / 0.6900". The C-mount specification has several dimensions associated with it:
http://nightvisionforumuk.com/viewtopic.php?t=5790&start=60
C-mount = 1"-32-UN-2A
http://en.wikipedia.org/wiki/C_mount
UN-2A = 60°
http://en.wikipedia.org/wiki/Unified_Thread_Standard
Lens Flange Focal Distance 17.52mm
Camera Depth (C-Mount Face to Image) 17.52mm
Length of Lens Thread 3.80mm
Mounting Thread 1" x 32 tpi UN 2A
The XC-75 C-mount lens will be used to examine the target ablation pit, and documentation for the Horiba ISA Jobin Yvon Sofie IC wafer interferometric system suggests the (cheap) Computar F1.8 50mm macro lens it uses may be suitable, but with a planned 50µm diameter beam focus this lens may not be long enough.
b. BEAM PROFILER LENS
I bought a Startech Instruments 'BIP-5100-Z beam profile lens' for just $50 after I read its datasheet and discovered it is supposed to be a UV laser beam profiler lens that also converts UV to visible, but I was unsurprised to find its expensive UV to VIS converter was missing. I should be able to use it as an ablation pit inspection lens. Datasheet and manual at link below.
3. COHERENT LASERCAM II 1/2" LASER BEAM PROFILE CAMERA
I never expected to find one of these on eBay usa for $50 and I never expected to win it at that price. I bought the other cameras because they seemed the closest I'd get. The LaserCam was designed for use with Coherent's BeamView software, hardware and associative frame store of yesteryear. Long ago I found the hardware cropped up, usually at high prices, and although you could download the software, it wouldn't work unless you bought a licence and that ran into $1000 or more. Understandably I abandoned that idea. Given all of the above and having already acquired alternative cameras, you may wonder why I bought it. The answer is this early version of the Lasercam is just a camera with a standard video output, and these days a USB video frame grabber costs pennies. The LaserCam comes with a 1300:1 OD VIS-IR filter which when removed allows it to be used down to 190nm. The Cohu 4812 matches this, but is a general purpose camera compared to the LaserCam dedicated profile camera. I'll use the Cohu first and once I'm certain I won't blow it up, I'll use the LaserCam (although another in Coherent's range looks uncannily similar - perhaps the LaserCam is actually just a Cohu in a rectangular box?).
4. PYROELECTRIC SENSORS (PE)
Molectron Q20 5W/cm² avg 0.1J/cm²/1µs max 20x20mm pyroelectric quadrant sensor 100µm central gap
This was sold as a separate assembly, missing its PQD-220 probe housing (see photos below).
It will be used to produce an initial focus of 100µm.
The Eltec 420-1-1J pyroelectric sensor includes a filter that blocks wavelengths below 2µm. Its datasheet says rise time is typically 2ns, and app note 109 indicates it can withstand a 20MW pulse.
It will be used for verification of experimental lasers with wavelengths above 2µm (e.g. CTH:YAG, CO2).
Molectron Q20 sensor & how it's normally mounted in its PQD-220 probe: Eltec 420-1-1J:
5. FAST RISE TIME PHOTODIODES (PDs)
The Newport Optics 818-BB-20/21 series of non-amplified fast PDs are probably what first comes to mind when considering a self-contained PD module that can drive a 50Ω load such as the 7A29 vertical plugin on a Tek 7104 oscilloscope. It consists of a PD powered by a lithium coin cell battery keeping noise to an absolute minimum. Rise time varies from 1.5ns to 175ps depending on the model but the faster they are the more expensive, with the 300ps 818-BB-21 coming in at $450 new https://www.newport.com/p/818-BB-21 and at least $150 used on eBay USA. Inside they are quite simple, see datasheet below.
The modules are very compact, but still intrusive (the idea of using a PD started out as an alternative to the restrictive bulk of a PT). This and the high price pushed me to the DIY route, and an eBay USA $10 Motorola MRD500 1ns typ 300nm-1100nm PIN PD seemed a good start. I also explored faster options.
DIY fast PD detector based on MR500 PIN:
6. AVALANCHE PHOTODIODES (APDs)
PTs are bulky and require EHT; APDs offer high speed and sensitivity down to single photons when operated in Geiger-mode beyond their breakdown voltage. Those on eBay are often relatively slow, usually intended for rangefinders. It would be desirable to obtain a 1064nm sub-ns rise time APD to determine the absolute start of the optical pulse but I found none affordable. I also explored the possibility of reducing rise time by cooling the PD with a TEC and came across a rather amateurish paper [E60] that revealed I'd probably need LN2 to get any significant effect. I still wanted to experiment with Geiger mode and in 2016 some $10 1983 RCA C30956E 2ns APDs appeared on eBay USA in unknown condition:
Moving on to 2022 and eBay now has GHz FO communication InGaAs PDs at affordable prices:
LSIPD-A75 2.5GHz 140ps InGaAs PD 800nm-1700nm PIN $12 from Beijing Lightsensing Technologies, or
Perkin Elmer C30617 3.5GHz 70ps typ InGaAs 800nm-1700nm PIN dated 2001, $24, Which is a better specified modern version of the
RCA C30617 3.5GHz 100ps typ InGaAs 1000-1700nm from the late 80s:
7. TRANSIMPEDANCE AMPLIFIER (XZamp)
The Newport BB PD series has a simple 50Ω output drive circuit with no amplification and if the optical signal is low level, there will be insufficient drive for external circuitry. A transimpedance amplifier
converts the current output of a PD to a voltage. It is relatively easy to build and cheap modules are available on eBay China but they are far too slow. A better route is an instrument designed for the purpose, and the obsolete 350MHz Melles Griot 13AMP007 is a reasonable choice. Its datasheet indicates a typical rise time of <1ns when combined with a Melles Griot 13DAH001 350ps Trise PD, and it includes bias offset drive to ±20V. It accepts currents up to 160µA and voltages up to 8mV. These values correspond to amplifier fixed gain in current mode: 6250 x 160µA = 1A, and voltage mode: 125 x 8mV = 1V.
Combined with one of the above InGaAs PDs it should give <<1ns rise time.
8. PD XY POSITION MONITOR
In 2022 I found a United Detector Technologies UDT-30A Position Monitor on eBay USA for $8.50 albeit with $40 shipping to the UK but either way a bargain as it provides a means of readily checking out segmented PDs, although I could find no data for it on the web (probably why it was only $8.50). This instrument is a differential transimpedance amplifier designed for quad PDs, and provides XY position analogue meters and output voltages, and works with normal common-cathode (CC) quad PD sensors.
The nearest UDT part I could find to match the naked hexagonal 5-way socket on the front panel was a UDT-1233 cable assembly with a very deep socket on one end and a 7-way hex plug on the other and at $90 I wasn't going near it, see photos. The deep socket accommodates long pin detectors like the UDT SC/10D quad PD, see below right. Page 7 of the datasheet below for the UDT-301DIV signal conditioner lists other 12xx cable assemblies, and its spec on page 6 hints at likely output voltages on the UDT-30A.
UDT calls the SC/10 quad PD a Tetra-Lateral Position Sensing Detector (PSD), see brief spec on Page 57 of their sensors catalogue below (in those days the sensible description 'quad pd' hadn't been coined so they overcomplicated it with TechSpeak 'tetra' 4 sides & 'lateral' adjoining). A detailed PSD description is on page 13, and page 14 Fig.13 depicts a PSD XY detector schematic, probably what is inside the 30A. However the SC/10 is a common anode (CA) quad PD, therefore incompatible with the 30A.
I assume the 30A mates with the equally expensive ($36, eBay) Wire-Pro 126-217 plug (photo below), unheard of in the UK. Given the high prices, I'll replace the connector with a cheap audio round DIN.
I found the 30A is wired sensibly with the common cathode on the centre pin and the remaining pins aligned with corresponding PD positions.
I made a little test jig with four **unknown but identical PDs in sockets wired with a common cathode to individual wire wrap socket pins aligned to the 5-way connector on the front of the UDT 30A, see below.
I shone a 1mw HeNe laser [Personal LIBS: Project Lasers, #14] into each PD in turn and noted the meter deflections and output voltages on the X,Y back panel BNC connectors. Test results from my lab book (photo on right) were with RANGE=Low, LIGHT LEVEL=Medium, SENSITIVITY=Min (at Max I got 12V instead of 1V). **PD spec unknown; from one of my random parts boxes.
Test jig fits into 5-way connector 1mW HeNe laser lights PDs Laser between PDs X= +0.01V Y= 0.00V
Top LH PD X= -1.02V Y= 0.00V
Bot LH PD X= 0.00V Y= +1.15V
X Y X Y
TL PD= -1, 0 TR PD=+1, 0
BL RD= 0,+1 BR PD= 0,-1
Top RH PD X= +1.15V Y= -0.01V
Bot RH PD X= +0.01V Y= -1.14V
9. SEGMENTED PHOTODIODES FOR FOCUS & POSITIONING
Optek OPR2100 quadrant sensor 6 x 6mm 400-1100nm 6-PDA with 46µm x 57µm central gap.
Pacific Silicon Sensor QP50-6 quad PDA 400-1100nm, 18µm sum and difference amplifier module.
The OPR2100 6-section PDA detector provides the means to measure focus to below 46µm.
Later I found the Pacific Silicon Sensor QP50-6 quad PDA sum and difference amplifier module with an 18µm gap at a great price and bought it. This takes all the work out of driving and detecting a quad PDA and has a finer resolution.
The combination of PDA/PE sensors are to assist ablation laser focus to 100µm, 50µm, 20µm.
Focus will be determined separately by comparing the voltages on each PD segment. The closer they all are to zero, the finer the focus.
Beam position is determined using a difference amplifier. Beam position is still needed to ensure it is actually within the bounds of the quad PD.
The UDT 30A will facilitate manual experimentation of beam position with the unbuffered sensors.
However they are all quite slow and it remains to be seen if this idea will work with a Q-switched laser, although a CW diode laser, see [Personal LIBS: Project Lasers] would also work; focus varies with wavelength, and a future experiment is to determine if a CW NIR LD can emulate a 1064nm Nd:YAG passing through HG NLOs, see [Personal LIBS: Non-Linear Optics]
Manf Device Elements Type Spacing Bandwidth
Molectron Q20 4 pyroelectric 100µm 200Hz
Optek OPR2100 6 PDA 46µm 55kHz
Pacific Silicon Sensor QP50-6 4 PDA 18µm 250kHz
If not, there is one more device I can try, in two versions:
EG&G SGD444-4 4 PDA Tr 10ns 125µm 45MHz
EG&G YAG444-4 4 PDA Tr 8ns 125µm 60MHz
I suspect the UDT 30A will be too slow for these and I will need to build my own high speed circuitry.
A small portion of the beam will be split off, attenuated and centred on the chosen quadrant sensor. When charge is equal across all PDs, the focus will be finely tuned using a beam expander until the beam focus point falls just within the central gap on the sensor.
This plan will need more thought to ensure the target is focused: a beam profiling camera may be a better way to do it - a beam expander before it would make it easier to measure the width of a tightly focused beam. Alternatively, an ablation pit camera confirming focus indirectly from the pit diameter.
I expect in reality it will be very difficult to focus down to 100µm, let alone 18µm.
POPR2100 6-element PDA PSS QP50-6-18U-SD2 quad PDA EG&G YAG444-4 quad PDA
THE GOOD, THE BAD AND THE UGLY
Below, the expensive looking gold-plated EG&G YAG444-4 pinout deserves a little section all by itself.
Look at the photo of its reverse on the right. EG&G added what they considered useful labels to the pins: C,A,A,A,A,R.
Any normal engineer seeing this would immediately thank them for identifying four anodes and a common cathode as wiring it the wrong way round would be certain death.
Now look at the photo of its datasheet to the far right.
That's right, EG&G is alone in the world in thinking
C should mean common ANODE and A must be active CATHODE.
Much to my disgust and embarrassment I forgot the seller had provided a pinout diagram. Instead I took the pin marking as gospel and fell for the gotcha.
I was lucky to get the YAG444-4 as they rarely come up but I found BMI Surplus had the inferior SGD444-4 for $30, mounted on what I assumed was a passive metal box as it only had a small connector like the one on the 30A, and I bought it. Of course I still faced the same incompatibility issue with the 30A, but it was the only affordable fast quad PD available, albeit as-is. I did discover the UDT-431 XY monitor has a switch selecting either format, but these are twice the size, and far more expensive than the $8.50
I paid for the 30A, so I went back to my original plan of building a bespoke high speed interface.
The SGD444-4 duly arrived and I found another, larger connector on it that wasn't in BMI's photo. There was also an Azimuth / Elevation label I hadn't seen before. Peeking inside I discovered what looked like a mil-spec PCB with onboard electronics, potentially solving the 30A CC dilemma and compensating for my earlier loss. No data of course. Teardown to follow, let's hope it still works.
10. PHOTOMULTIPLIER TUBES (PMTs)
The PCM spectrograph has an integral PDA enhanced by a MCP image intensifier, necessary to amplify low level atomic spectra. Initial attempts to find a way to gate the MCP to stop it being damaged by the laser and probably also Bremsstrahlung radiation, have been unsuccessful. Worse, I damaged the MCP control circuitry during my investigation, resulting in the MCP being stuck full-on, another sure-fire way of shortening its life but I hope I can repair it see [Personal LIBS: Prototype Integration].
Without an electrical means of shuttering the MCP I am left with the less desirable approach of gating the light into the MCP using an industrial quality stabilised optical chopper, see
[Personal LIBS: Spectral Gating].
Mechanical fluctuation and reduced repeatability of a motor can be limited to a degree by triggering the laser from the same shutter, preferably within 1 rotation. For the latter I propose a low power LD coupled through the shutter to an MR500 PD.
Later, I considered using the same shutter to Q-switch the laser, see [Personal LIBS: Q-Switches].
Shutter feasibility and indeed this entire plan must be qualified before I will risk it on the irreplaceable MCP/PDA, and an affordable alternative is to use a PMT in their place. To achieve this I acquired a set of four new Hamamatsu R6356HA 185nm-900nm sensitive PMTs with associated PSUs, drivers and amplifier circuitry at a knock down price, and some mu-metal sheet to block out unwanted radiation.
https://www.hamamatsu.com/eu/en/product/type/R6356-06/index.html
11. VACUUM PHOTOTUBES (PTs)
General Atomics IR 370nm-1350nm Tr 100ps, Tf 100ps, 1350V max
Hamamatsu R1193U-02 185nm-650nm Tr 270ps, Tf 100ps, 2500V max
Hamamatsu C3463 1.5kV / 2.0kV / 2.5kV EHT PSU for PTs
Vacuum PTs are typically used for laser detection where the light level is relatively high. By the use of a very high bias voltage they offer very fast rise and fall times. I bought two PTs covering the range of wavelengths used in the LHC. Amazingly I got the Hamamatsu PT and EHT PSU and cable on eBay USA for only $30. PTs will be used to initiate timing from detection of laser optical pulses.
The GA PT has an enhanced IR spectral response and is similar to the ITT F4014 listed on page 8 of the
[306p07], 1974/1975 ITT Electro-Optic Devices data summary, below:
Below left, Hamamatsu R1193U-02 & PSU Below right, GA enhanced IR PT
2. VISUALISERS
These convert invisible wavelengths to visible.
1. IR TO VIS CONVERTER
Chinese IR card
2. UV TO VIS CONVERTER
Even though generation of 193nm is probably beyond my means, I wanted to be sure to convert it to visible light if I could. I sought an image converter able to go down to the limits of the Stellarnet spectrometer: 190nm.
Metrolux K7 20x20x3mm, absorption 110nm-350nm, emission 612nm peak
This optic fluoresces in the visible spectrum when exposed to UV light. After attenuation I will use this to visualise the final output UV beam on a CCD camera to ensure the beam profile meets its needs (Cohu 4815 CCD camera est. 0.75 sensitivity at 612nm).
Other manufacturers offer similar products but they too are very expensive.
Ophir: 'Our UV image converters consist of fluorescent discs that convert the UV radiation that is difficult to detect by CCD cameras into visible light, which in turn is directed to the camera. These fluorescent discs are specially designed for UV conversion and have high light output, a large linear dynamic range and a **high destruction threshold. 1X UV image converter: Screw on. For beam intensities from 50µJcm² to 15mJcm². Fits 4.5mm recess and CS mount cameras, part SPZ17023'[306p26], from their 2022 catalogue, [O40]. [**I don't call that high!]
Gentec has a similar line of converters, see downloadable catalogue page: [O39].
Metrolux has since deleted their converter webpage but fortuitously I had taken a copy of its text:
'To expand the wavelength range accessible for laser beam profiling, suitable cameras are being supplemented by converters. UV converters turn UV light into visible light while IR converters turn IR light into visible light. Depending on the specifications we offer a variety of phosphorus coatings and glass converters':
Product Type Wavelength Decay (10%) Emission Peak = Cohu 4815 Peak Val
- - - - 720nm 1.00
K2 Phosphor 1nm-400nm 1ms 545nm 0.67
K6 Fluorescence 110nm-350nm 4ms,5ms 542nm 0.66
K7 Fluorescence 110nm-350nm 3ms 612nm 0.75 <<<<<<<<<<<<<
K8 Fluorescence 110nm-350nm 2µs 405nm 0.40
NIR Phosphor 1495nm-1595nm - 800nm/1050nm 0.74/0.05
CIR Ceramic 1064nm/1550nm - -
Size/Name K2 K6 K7 K8 NIR CIR Prices [2017]
CCD £ - - - x - £947.30
Ø10 x 1mm - x x - - -
Ø25 x 1mm x £ * - - - £370.32
Ø25 x 3mm - £ £ x - - £327.26 £305.73
20 x 20 x 3mm: K6 K7 £180.85
'The damage threshold of the converters is in the range of 0.5J/cm². But to keep the linearity of the sensors the energy density should not exceed the 20mJ/cm² saturation level.'
As you can see, they are eye-wateringly expensive so first I looked for cheaper alternatives.
Manufacturers add a UV fluorescing compound to detergent to make whites appear whiter, and I tried dipping a frosted microscope glass slide into the solution but it didn't fluoresce at all.
Website [W6] describes a photographic DIY UV converter using inorganic phosphors in acetone, but only mentions peak absorption at 254nm minimum with peak emission at 525nm. Halfway down it says UV-enhanced image converter tubes down to 180nm are available for the UV 'Find-R-Scope', but these are very expensive. The RCA 6032 image converter tube is listed as an alternative for DIY use but its S1 phosphor only goes down to 300nm, see page 6 of [D44] 1974-1976 ITT Electro-Optic Devices Summary.
Unfortunately whenever papers show absorption, they always seem to stop at 200nm. Whether this is because they lack the equipment to go lower or they have no interest below 200nm is not apparent. The following paper is no exception, but the graph is so high at 200nm, Europium likely absorbs 193nm:
Fig.1 in [306p27] suggests Eu absorption rises downward around 450nm and extends well below 200nm:
'A high-efficient blue-light excitable red phosphor: intramolecular p-stacking interactions in one di-nuclear Europium (III) complex', Dalton Transactions', Z.Wang, H.Yang, P.He, Y.He, December 2015
https://www.researchgate.net/publication/286381369
I found an eBay USA seller offering Europium powder with the claim it fluoresces vividly under UV, but I could not find a liquid medium to apply it.
An ex-USSR eBay auction offered a blue X-ray scintillation screen using V5A400 / Ytterbium, and a green screen using ZU-1 / Yttrium. At $14 for a 4" x 4" piece, I saw no harm in buying it to experiment with but when it arrived I was surprised to find it seemed to consist of a thin piece of cardboard coated in coarse crystals. I wanted a fine transmissive screen, not a rough opaque target.
Another auction offered an 'X-ray scintillation fluorescent screen' for $6 including shipping to the UK, describing it as 'emitting light upon excitation by X-rays and charged particles generated during decay of atoms, using copper-activated ZnS on a crystal clear 1.5" diameter substrate', with a claim it glowed brighter than the more common silver-activated ZnS. This will likely work with DUV but it is papery thin and seems as delicate as the USSR cardboard type, with no indication of damage threshold.
[O40], Phosphor Handbook, 2nd Ed., P.275 discusses ZnS:Cu and ZnS:Ag properties, mentioning they are used in CRTs and Tek commonly uses P31 green from the same compounds:
http://w140.com/tekwiki/wiki/Phosphor
Fig.2 in [306p28] suggests Zns:Cu absorption rises downward around 250nm and extends well below 200nm: 'Probing the local structure of dilute Cu dopants in fluorescent ZnS nanocrystals using EXAFS',
B.Car, S.Medling, C.Corrado F.Bridges J.Zhangb, 17 July 2011
https://www.researchgate.net/publication/51579595
I wondered if I could cut a small piece from an oscilloscope CRT phosphor screen, but a friend pointed out it would degrade once out of a vacuum. Perhaps a DUV-passing protective coating could be added to protect it, but I remember buying a commercial solar cell secured onto a metal plate with so-called
UV-proof lacquer that turned opaque after 10 years in the sun, and DUV is particularly aggressive.
Eventually I gave up and just bought the cheapest Metro k7 phosphor.
A few years later I came across UK company Phosphor Technology Ltd who kindly sent me a small sample of their QK63 phosphor powder, adding it could be dispersed in acetone or diluted PVA paste and would visibly fluoresce ~630nm whilst absorbing at 193nm [306p29], and I still have that experiment to run.
3. DIFFUSERS
Diffusers provide a means of both defocusing a beam and making a visible beam more visible and I will likely need one for the UV to VIS phosphor converter. The 1064nm diffuser will assist beam profiling.
Diffuser UVFS 1" Thor DGUV10-120 120 grit
Diffuser UVFS 1" Thor DGUV10-220 220 grit
Diffuser, opal, 1064nm
4. HORIBA/SOFIE LASER INTERFERMOETER
I bought this initially just for its Computar 50mm F1.8 lens, but also explored its functionality, see
[Repairs: Horiba / Sofie Teardown].
5. OPTICAL SHEAR PLATE INTERFEROMETER
In 2014 I found a Thorlabs Si254 10-25mm beam, optical shear plate on eBay for $75 ($266 new).
Curious, I found a bare assembly at a US Surplus shop BMI for $115 (missing a dowel, see
[Repairs: General Repairs]) and also bought the SI254 even though it was too big, to experiment with until I found a smaller one, total outlay $185 vs combo price $602 new. In 2019 I found a cracked Thorlabs SIVS shear plate magnifying viewer for $10 ($380 new) that I hoped would improve the chances of using the SI254. The crack is only on the frosted screen and I may be able to substitute the normal one which has to be removed to fit the magnifier in its place. In 2022 I found a 5-10mm Si100 for another $75 ($228 new) and bought that too. Maybe in another 8 years I'll find a SI050 2.5-5mm to complete the set! https://www.thorlabs.com/newgrouppage9.cfm?objectgroup_id=2970
Thorlabs' website provides scant information on the optical properties of their wedges.
Newport Optics reveals the details of their 20QS20 2" wedge here:
[O54], Newport Optical Shear Plate Collimation Tester AN 25, '9.4mm thick, wedge 4.4±0.88 arc sec'.
I believe plates for smaller beams have a larger wedge angle.
This excellent video explains how to use all of these parts: https://www.youtube.com/watch?v=iNgD4UKAuXg
Above far left: Thorlabs shear plate bare body; right: magnifying viewscreen with cracked frosted screen
Below left: Thorlabs SI254 shear plate for 10-25mm beams and far right, SI100 for 5-10mm beams
6. UV/IR ELECTRO-OPTIC IMAGER
Photon View 350nm-1550nm imager
I could not resist this at the bargain price of $75. Its label suggests it's designed for professional optical applications but externally it resembles an early commercial IR night sight, proven by a teardown photo at the Queensland University Physics Museum:
https://physicsmuseum.uq.edu.au/infrared-image-conversion-viewer
Coherent sold it an an elevated price so I suspect they bought the manufacturer. It contains a removable high pass IR filter (bottom left) that I found blocks out anything below 715nm. With the IR filter removed I illuminated it from a simple Bausch & Lomb UV monochromator fed by the PCM-401 UV Hg calibration lamp (below right) and confirmed it fluoresced down to the 253.65nm line (the Stellarnet shows this line at 251.7nm because I incorrectly aligned its green measuring marker left of the peak).
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