Measuring femto-level differntial capactiance changes - Page 1
Forum section: electronics / general

author: charliehorse55
author_rank: Contributor
timestamp: June 04, 2024, 05:52:37 am
content: My dad is a semi-retired physicist and he's interested in building a gravitational wave detector. The idea is to measure the differential change in capacitance of 2 capacitors oriented at 90 degrees. Gravity waves push the plates of the capacitor back and forth, causing the voltage on the capacitor to change:The 0.1 ohm resistor is to filter the low frequency components (mainly drift due to internal leakage).We're aware that we won't be able to observe anything with an experiment that fits into our cost/complexity budget, but the idea is to develop the technology to understand what would be required for a full-scale system. By creating smaller and smaller test inputs (for ex. mechanically vibrating the capacitor), we can validate how sensitive the instrument is, and how much it would have to improve in order to observe gravitational waves.Ultimately, the signal will be buried in a lot of noise and require signal processing techniques to extract, so the amplifier needs enough gain to amplify the inherent noise to cover the entire range of the ADC (with room to prevent clipping). So, the lower the system noise, the higher the gain.Frequency: 50-4kHzGain: noise floor (100nV?) -> 1V for a 3V ADC = ~10 million V/V = 140dB?Should we use discrete transistors for some sort of input stage, or directly go into a low noise op amp such as LT1128?Is there a practical limit to how much gain you can put onto a single op-amp stage? The LT1128 has >75MHz GBW, which would imply for 4kHz a single stage could already have a gain >10,000. Such high value resistors add noise of their own?How many stages of amplifier should we use?The source impedance here should be the ESR of the supercapacitor, which is extremely low. Could a small signal transformer be used? Do they have any non-linear effects that might destroy a femto-level signal?How to implement the 50Hz filter on the input? The required value of R for Fc=50Hz would be something in the ~10 uOhm range, which would get dwarfed by the internal resistance of the caps. A simple RC pole would introduce too much noise through the resistor, right?I have little-to-no experience with analog design, so I'm kinda jumping into the deep end with this!

author: jonpaul
author_rank: Super Contributor
timestamp: June 04, 2024, 06:55:53 am
content: see the many articles and papers on capacitive sensors, and the basic equations for a 2 plate parallel capacitor.The best G wave sensors today use special lasers and not Capacitive, and use masses of about 1000..10000 kG.Jon

author: iMo
author_rank: Super Contributor
timestamp: June 04, 2024, 07:14:42 am
content: The first step would be to estimate a capacitance change when your capacitor's based system will be hit by a typical wave the LIGO/VIRGO/etc detect today.

author: Kleinstein
author_rank: Super Contributor
timestamp: June 04, 2024, 07:15:08 am
content: Capacitive sensor read out is a common thing. It is sensitive, but by far not good enough to detect gravitational waves. It could still be something to experiment with and look at things like therma expansion, vibrations and seismic signals.For best sensitivity discrete transistors (JFETs or maybe MOSFETs) have an advantage. The LT1128 and other BJT based parts are not really suitable because of there current noise, that is an issue, unless one operates at rather high frequencies.

author: iMo
author_rank: Super Contributor
timestamp: June 04, 2024, 07:18:03 am
content: Quote from: iMo on June 04, 2024, 07:14:42 amWiki:QuotePS: my estimation - a 10m*10m large plate capacitor, with 1mm plate distance, X7R dielectric, would change its aprox 3600uF capacitance by 0.0000000036fF..

author: charliehorse55
author_rank: Contributor
timestamp: June 04, 2024, 07:47:23 am
content: Quote from: Kleinstein on June 04, 2024, 07:15:08 amI thought current noise won't be a problem because the source impedance is so low? A 3000F supercapacitor probably has a source impedance in the tens of milliohms, so the <1nA current noise becomes some pV of voltage noise, which would be orders of magnitude less than the 10-100nV voltage noise?

author: charliehorse55
author_rank: Contributor
timestamp: June 04, 2024, 07:54:03 am
content: Quote from: iMo on June 04, 2024, 07:14:42 amIt's somewhere around 10^-20 to 10^-24. LIGO measures somewhere around 10^-22

author: Dr. Frank
author_rank: Super Contributor
timestamp: June 04, 2024, 08:01:07 am
content: I'm as well an experimental physicist, so I suggest to find other applications for measurement of small displacements, than Gravitational Waves.Anyhow, you'd need extremely stable capacitors, so I guess the design of such a capacitor cell would be the most crucial problem in your experiment.It would as well be necessary to design a capacitance bridge configuration.. very delicate.. somehow reinventing the wheel.In the 1990ties, at Aachen University (RWTH), a colleague of mine made measurements on 'Magnetostriction and Thermal Expansion of High Temperature Superconductors', for his PhD thesis, using an absolute (direct) capacitive method to detect very small length changes. I don't remember the resolution any more, might have been on the order of nm.We have used a GENRAD 1620 Bridge first, which allowed to measure 10-5pF or 10aF changes.Later, we bought an automated and more stable electronic bridge, an Andeen-Hagerling AH 2500A, which allowed 0.5aF resolution, much faster and with comfortable GPIB readout. This brand is still available, I guess model 2700 is the most recent one. I propose to buy one of these, used. Maybe it's possible to measure capacitor differences as well.Frank.http://www.andeen-hagerling.com/ah2500a.htm

author: nimish
author_rank: Regular Contributor
timestamp: June 04, 2024, 08:37:47 pm
content: Quote from: charliehorse55 on June 04, 2024, 05:52:37 am10 min on google scholar:https://arxiv.org/abs/2306.08124money shot on page 12

author: shabaz
author_rank: Frequent Contributor
timestamp: June 04, 2024, 10:48:35 pm
content: Hi,I know nothing about the such a use-case, so I could be totally wrong, but perhaps it could be worth examining to rule in/out TI's FDC range (e.g. FDC2214), they can operate in a differential mode, and can sense tiny changes with 28 bit resolution, and very low noise, and supports measurements up to 4 ksps, although that rate is if only one channel is measured. There are low-cost evaluation boards for the FDC series.I played with one for a bit, you can do neat things with it such as create dust sensors and so on, detected by the minute change in capacitance.Technically it doesn't measure the capacitance directly, instead, it measures the frequency of oscillation of a tank circuit (LC circuit), to 28-bit granularity.

author: Doctorandus_P
author_rank: Super Contributor
timestamp: June 05, 2024, 12:32:43 pm
content: Capacitive measurements are quite common. I have a kitchen scale that has a spring (in about the same shape as a load cell) but also two metal plates (approx 60x80mm) and measures the capacitance (and thus distance, and thus spring tension) between the plates. It's a pretty old scale.Capacitive measurement is also common for calipers (especially the cheapest digital ones) and for rotary encoders. (Up to at least 20 bit)But for a gravity wave detector? My first guess is that you are at least 5 orders of magnitude off with your estimated femto Farad resolution, and the rest will get swamped by vibration and other noise sources. Or, at least when we're talking about the same sort of thing:https://en.wikipedia.org/wiki/Gravitational-wave_observatoryThese things are between several hundred meters and multiple kilometers long, just to get enough signal to have any hope of being to measure something. Working on this in your backyard is just as bonkers as on "Free energy".

author: Conrad Hoffman
author_rank: Super Contributor
timestamp: June 05, 2024, 02:19:42 pm
content: As Dr. Frank points out, the old GR transformer based capacitance bridges are the bomb for this. Download the manual for the 1615 and 1620 to see how they do it. If you have only a single value to measure/compare, you could wind your own transformer for the measurement, but used bridges are under $1k. I've never seen an affordable Andeen bridge for sale, unless $3k is in your budget. They studied the GR bridges for a long time before designing theirs.

author: RoGeorge
author_rank: Super Contributor
timestamp: June 05, 2024, 02:22:00 pm
content: I'm curious about the 3000 Farad capacitance, that is a huge value. How, or what of, are the capacitors made?

author: tggzzz
author_rank: Super Contributor
timestamp: June 05, 2024, 05:28:24 pm
content: Quote from: charliehorse55 on June 04, 2024, 05:52:37 amLIGO sensitivity: At its most sensitive state, LIGO will be able to detect a change in distance between its mirrors 1/10,000th the width of a proton! This is equivalent to measuring the distance to the nearest star (some 4.2 light years away) to an accuracy smaller than the width of a human hair.https://www.ligo.caltech.edu/page/factsCompare and contrast that with the changes in capacitance you have mentioned.Compare and contrast those capacitance changes with those due to Brownian motion and shock/vibration.

author: iMo
author_rank: Super Contributor
timestamp: June 06, 2024, 05:26:40 am
content: All that written above make me quite curious how the people at LIGI/VIRGO/etc. provide the measurements actually.I somehow doubt they just do measure a single pass through the tube with messing with X/Y interference afterwards, perhaps they do a "multiplication" of the path the photons travel through the pipes - like somehow none-planar mirrors where the photons pass the tube length many times actually (ie 1 billion times)..PS: Well, 1 billion times multiplied by 4km would be too far, so - say 10000x..PS1: the large supercapacitors have to be cooled down to near zero, imho, otherwise the chemical reactions and thermal vibration will mask any measurements. Perhaps SpaceX will be ready to provide a fleet of Starships soon, such you may create a 1000km x 1000km large plate capacitors with 0.1mm plate distance which might indicate ~100fF differences..

author: RoGeorge
author_rank: Super Contributor
timestamp: June 06, 2024, 05:56:41 am
content: Don't know the details, but the path is under vacuum, mirrors are cooled and sited on very elaborated active vibration cancelling platforms, plus a lot of measurements averaging and a lot of DSP postprocessing. It is so elaborated that the first time they detected something, everybody assumed the signal might have been a processing artifact, or maybe an inside joke from other coworkers.

author: rteodor
author_rank: Frequent Contributor
timestamp: June 06, 2024, 06:00:47 am
content: Mandatory Veritasium video on the subject:[The Absurdity of Detecting Gravitational Waves]https://youtube.com/watch?v=iphcyNWFD10I just can not see how this can be done even with supercooled capacitors. It is a nice thought experiment thou.

author: dietert1
author_rank: Super Contributor
timestamp: June 06, 2024, 06:31:02 am
content: Don't know much details either but i assume there is huge disturbance from the rotation of our planet in the gravitational field of the sun. Probably they need to suppress this by high pass filtering and only detect gravitational waves at time scales much below an hour or so.Another problem is that those neutron star/black hole events that generate strong enough gravitational waves are rare and the longer you wait, the more noise events.So if you detect "once per hour" and you have to wait 5 years, you need about 9 sigma discrimination, in other words a sensitivity much below the expected effect. It's difficult to understand how they excluded some kind of planetary recoil event. A space based confirmation would be interesting.Regards, Dieter

author: RoGeorge
author_rank: Super Contributor
timestamp: June 06, 2024, 06:40:44 am
content: The detected oscillations at LIGO are in the audio range.

author: iMo
author_rank: Super Contributor
timestamp: June 06, 2024, 07:24:59 am
content: Quote from: iMo on June 06, 2024, 05:26:40 amThe guy in the Veritasium video above said the laser pulse is at MWatt level. That may indicate they let the pulse bounce many times between the mirrors, thus doing the multiplication effect.. For a single pass they would not need MW pulses..PS: thus for example with 10000x bounces the pulses travel 80000km in X and Y, the X-Y difference could be roughly 80 fm, compared to the 1 um laser wavelength, for example.

author: rteodor
author_rank: Frequent Contributor
timestamp: June 06, 2024, 08:41:18 am
content: Quote from: iMo on June 06, 2024, 07:24:59 amQuoteThe way I understood it is thatinterferenceis the key. Big power is required because a lot of photons are needed to detect a minuscule interference (a trillionth of a laser wavelength). Put it another way: the amplitude of the signal resulted from the interference detector is very very tiny so the laser amplitude is boosted up to make that minuscule signal larger.It is an interesting question if multiple passes are used but I have a hunch that they are not. And that is because of the complications in the optics.Also another question is if there is a detection if the GW comes at 45 degree angle in the plane of the detectors. Would that be a "blind spot" ?

author: iMo
author_rank: Super Contributor
timestamp: June 06, 2024, 08:59:00 am
content: I've just asked ChatGPT4 what would be the maximum number of bounces between two mirrors and I've got, for example - see below. There will be a latency as you have to wait till the pulse arrives after the N-bounces, but you may timestamp them thus the latency cannot be a problem.PS:N.of Bounces = ln(SensThr/InitInt)/ln(MirrRefl)

author: iMo
author_rank: Super Contributor
timestamp: June 06, 2024, 09:51:39 am
content: But let us continue with the "thought experiment" - for example what is "almost practically doable within next 50 years" - an 1m x 1m x 1m large multilayer ceramic capacitor, eps_r=500 dielectric, 50nm dielectric and 50nm metal, 10 million layers, all around zero temperature, will give you aprox 1MegaFarad. That may generate 1femtoF X-Y difference (when the stack of layers changes by 1e-21)..PS: that will not probably work as the relative permittivity of most dielectrics drops with lower temperatures, almost to 1.

author: dietert1
author_rank: Super Contributor
timestamp: June 06, 2024, 10:26:24 am
content: Quote from: RoGeorge on June 06, 2024, 06:40:44 amOn their web page they write: "Consequently, the time they spend orbiting and emitting gravitational waves in LIGO’s detectable range is typically very brief, ranging from a fraction of a second to tens of seconds."I'd guess they can use signal processing to have something audible for the general public. They describe that procedure, too. Apparently the time between events is also shorter than 5 years, as they observed a dozen events since 2017.Regards, Dieter

author: iMo
author_rank: Super Contributor
timestamp: June 06, 2024, 10:33:49 am
content: The duration of the "orbiting" takes fraction of seconds to several seconds, but the "frequency of their orbiting" could be hundreds of Hertz easily, imho..

author: dietert1
author_rank: Super Contributor
timestamp: June 06, 2024, 11:41:46 am
content: They write: "LIGO can convert its space-time distortion signals into an audible sound called a chirp so we can all “hear” the final moments of the lives of two black holes and two neutron stars. While it’s likely that these objects had been orbiting each other for billions of years, LIGO captured the last fraction of a second or tens of seconds of those lifetimes together."Read here:https://www.ligo.caltech.edu/page/gw-sourcesRegards, Dieter

author: coppercone2
author_rank: Super Contributor
timestamp: June 06, 2024, 12:12:33 pm
content: 3.6 yoctofarad

author: KT88
author_rank: Frequent Contributor
timestamp: June 06, 2024, 12:44:24 pm
content: …and how would we get such a large capacitance in resonance at a high enough frequency?

author: iMo
author_rank: Super Contributor
timestamp: June 06, 2024, 02:25:05 pm
content: Quote from: dietert1 on June 06, 2024, 11:41:46 amIt is my understanding the two objects are orbiting each other slowly, and their angular velocity is low. Then, when they are much closer together, their angular velocity (of the orbiting around a central point of gravity) starts to increase dramatically, with maximum at the moment they join together. In this very moment, lasting that fraction of a second or tens of seconds, their angular velocity is at max (and could be quite high, ie. we have the milliseconds magnetars and quasars), and at this time they generate the max peak of space time distortion, imho. What LIGO can only detect is that very moment. Before that very moment of the joining (the moment==fraction of a second or tens of seconds) and afterwards the LIGO detects nothing..

author: dietert1
author_rank: Super Contributor
timestamp: June 06, 2024, 04:09:22 pm
content: On the page i linked they explicitly demonstrate how they use time-lapse to convert the detected signal into audible sound. But yes, there may be events where the last second or fraction of a second is audible without time-lapse.They use the chirp as a signature, but i didn't find their detection bandwidth. As far as i remember, a table tennis ball coming to rest on the table can also produce kind of a chirp..Regards, Dieter

author: charliehorse55
author_rank: Contributor
timestamp: June 07, 2024, 08:13:59 pm
content: Re: Being able to measure gravity waves:We aren't expecting to be able to measure them with this setup. 10^-20 to 10^-24 is a high bar to reach. We're aiming for something much more realistic with the first iteration of this experiment, say 10^-8 or better (10ppb). The idea is to verify the sensitivity of the instrument in stages, making improvements with each iteration. Eventually, the budget would start getting large and you'd need bigger and bigger grants. LIGO's total budget by the time it first detected gravity waves was probably over a billion dollars.Re: Measuring capacitance change using resonant frequency:Hadn't considered this approach, certainly seems to be worth investigating. After all, measuring time is something we can do extremely accurately. The best clocks in the world are 10^-18. That ANDEEN-HAGERLING capacitance bridge mentioned claims a resolution of 0.07ppm, about 10^-7.Alternatively, we have been looking at directly measuring the differential change in voltage that will appear at the capacitor terminals. Given that the total amount of charge stays the same, the change in voltage should be proportional to the DC voltage across the capacitor times the change in capacitance. For the first prototype, if you could build an analog system with a 1uV noise floor, and a 10V DC bias, you'd already be at 0.1ppm. Add in some DSP techniques, which can improve SNR for a known signal by roughly sqrt(n cycles) and you're approaching 10ppb for the type of signals LIGO sees.

author: dietert1
author_rank: Super Contributor
timestamp: June 07, 2024, 11:18:26 pm
content: Electromagnetic force is much stronger than the gravitational force and it's a disadvantage to use electrically charged bodies for sensing gravitational fields. If you read about LIGO, they made a strong effort to isolate their test bodies (=laser mirrors) from terrestrial forces along the sense direction. I'd guess the electrostatic force of the charged capacitor plates onto each other can already ruin the measurement and a solid body like a MLCC won't even be able to sense earth gravitation. There are many steps to take before even mentioning gravitational waves.Regards, Dieter

author: m98
author_rank: Frequent Contributor
timestamp: June 08, 2024, 01:07:54 am
content: Obviously, you can't really DIY a gravitational wave detector, especially not (entirely) with capacitive sensing, as the whole principle is based on measuring miniscule distance differences between orthogonal paths over large distances. So km-scale UHV vacuum chambers, multi-ton test masses suspended with advanced vibration isolation, ...Having worked on/with some interferometers derived from LISA Pathfinder, you definitely could build a heterodyne interferometer with sub-nm resolution for < 10k in material cost, provided you are not after the long-term stability needed for something like gravitational wave detection.

author: RoGeorge
author_rank: Super Contributor
timestamp: June 08, 2024, 06:24:12 am
content: The physics formulas we know, and use in electrical engineering (i.e. the ones related with the measuring capacitors), were all deduced by assuming timespace don't wobble. I'm not a physicist, but I remember some of the laws of electrostatics, and later electromagnetism, explicitly assume the symmetry and homogeneity of space, for example (sorry for the video, it's an explanation following the ideas in the Feynman's lectures):Maxwell's equations are intuitive! (Ep: 1 - Power of Gauss's Law)FloatHeadPhysicshttps://www.eevblog.com/forum/chat/fun-for-nerds/msg5130876/#msg5130876Maxwell's equation explained logically! (Ep 2: Faraday's law powers the world)FloatHeadPhysicshttps://www.eevblog.com/forum/chat/fun-for-nerds/msg5162484/#msg5162484The really funny question when it comes to detecting gravitational waves is which of the EE formulas will still stand true while stretching the timespace. I guess not many of them, if any.

author: rteodor
author_rank: Frequent Contributor
timestamp: June 08, 2024, 06:35:01 am
content: Quote from: charliehorse55 on June 07, 2024, 08:13:59 pmI guess there would be additional gain from the amplitude of the resonant circuit (assuming this method would be used). If that can be increased to 1 kV for example instead of 10 V there are two orders of magnitude gain right there. Same principle as in LIGO's detector.Later edit: ... and after seeing RoGeorge's post, assuming that there is capacity change. I do not understand what G waves are changing in terms of 1/sqrt (e_0 * u_0).

author: RoGeorge
author_rank: Super Contributor
timestamp: June 08, 2024, 07:16:44 am
content: Quote from: dietert1 on June 06, 2024, 10:26:24 amIf you mean they added a frequency shift to make it audible, they probably didn't. Saying this because of a YT comment I've just read this morning (the comment seems to be coming from somebody who works at LIGO):QuoteQuoted text is from the comments in this YouTube video:How does LIGO detect gravitational waves?Craig Cahillanehttps://youtu.be/X7RJHxeCulYMy understanding is the signal produced by LIGO detector goes up to 100Hz or so, and that signal is in sync with the space wobbling, so no frequency shift, but I don't really know any details about how they post-process the detected signal.

author: rteodor
author_rank: Frequent Contributor
timestamp: June 08, 2024, 07:36:23 am
content: Meanwhile, in a completely unrelated thread:Quote from: AlienRelicshttps://www.eevblog.com/forum/metrology/millimeter-range-water-level-sensor/msg5533791/#msg5533791

author: dietert1
author_rank: Super Contributor
timestamp: June 08, 2024, 07:44:30 am
content: Quote from: RoGeorge on June 08, 2024, 07:16:44 amYou shouldn't insist on your mistake. Why don't you just read at the LIGO website (link above)? They explicitly demonstrate that they apply signal processing to make the signal audible. They have a video that contains the original signal and the transposed signal. What you remember as audible is the treated signal. They don't say though whether they always have to do that or not..Regards, Dieter

author: RoGeorge
author_rank: Super Contributor
timestamp: June 08, 2024, 07:54:08 am
content: Quote from: rteodor on June 08, 2024, 07:36:23 amAnother topic with a very sensitive capacitors-bridge was this onehttps://www.eevblog.com/forum/projects/suggestions-for-high-resolution-tiltmeter-(inclinometer)-sensor/msg1565554/#msg1565554

author: iMo
author_rank: Super Contributor
timestamp: June 08, 2024, 08:07:57 am
content: We have to to place beacons on several bodies in our Solar system (ie. Mars, asteroids, moons of Jupiter/Saturn). Beacons with high stability, sending signals we can then evaluate and based on the phase differences we may get better info on the space-time wobbling..

author: babysitter
author_rank: Frequent Contributor
timestamp: June 08, 2024, 08:40:35 am
content: The planned LISA is a array of 3satellites, intending exactly to realize a extremley-long-baseline interferometer.The TO setup might, howver, be interesting for seismic research.BRHendi

author: iMo
author_rank: Super Contributor
timestamp: June 08, 2024, 08:45:55 am
content: Quote from: RoGeorge on June 08, 2024, 07:16:44 amSo they indeed use the multiplicative effect of the "roundtrips between the mirrors" - not in form I thought above ("the bouncing N-times between the mirrors") but in form of the Q of the cavity where the Q depends on the mirrors reflectivity (13:21)..

author: RoGeorge
author_rank: Super Contributor
timestamp: June 08, 2024, 11:22:18 am
content: Quote from: dietert1 on June 08, 2024, 07:44:30 amIndeed, I was wrong about that one, sorry. Sometimes they do shift the frequency to make it more audible, even if the detected signal of LIGO is still in the audio range. Found such an evidence starting from the Caltech link, and searching for other signals on the same YT channel, there is this half minute video where the detected signal vs the audio-enhanced signal are shown side by side:https://youtube.com/watch?v=JKBBVgR991sMeanwhile they improved on the lower detectable frequency, too, from 40Hz minimum to only 10Hz now.QuoteQuote from:https://advancedligo.mit.edu/summary.htmlI was curious about the exact frequency range of the signal produced by LIGO, but could find any clear specification, only indirect hints.Quote from: iMo on June 08, 2024, 08:45:55 amYou assumed correctly.Maybe the Fabry-Perot cavity is not stressed enough in most popular videos about LIGO. I didn't register an optical cavity was inserted in the LIGO arms, until watching that video.This is funny, you can drag the mirrors and observe the effect live:https://ccahilla.github.io/fabryperot.html

author: iMo
author_rank: Super Contributor
timestamp: June 10, 2024, 06:38:23 am
content: Yep, the "megawatt pulses" mentioned in the above YT video was for me the first indication they have been using a strong multiplicative effect of some kind, otherwise there will no need for such power in a 4km long arm. I have to refresh my math - as what could be the transformation between the Fabry-Perot equations and the simple N*arm_length path multiplicative effect..That reminds me on the "superregenerative" receivers (I built several in my teen age for my RC models) where in the single transistor stage you may get X million amplification. Similar with "audion" (the "regenerative" receivers)..PS: having a supercapacitor in X and a superinductor in Y, both creating LC in a superregenerative receiver as a g-wave detector

author: RoGeorge
author_rank: Super Contributor
timestamp: June 10, 2024, 08:22:26 am
content: Quote from: iMo on June 10, 2024, 06:38:23 amMy understanding is that the MW of power do not enter into the interferometer. The guy in the Veritasium's video (iphcyNWFD10) is the manager/PR, note how he rants childish and laughs at his own joke. Instead of answering, he is saying something like "if all contracts [including the space and the wavelength] then we can't detect anything, so it can not work, let's all go home now".Anyway, from the other video (X7RJHxeCulY), the one with some math in it, the mentioned power is kW, not MW, and somebody in the comments asked about the power discrepancy, MW vs kW. IIRC the explanation was that the LASER did shoot a MW power pulse, but the light enters first in the triangular-shaped formation of mirrors on the left, which is supposed to clean the frequency and the amplitude variations in the light coming from the LASER (input cleaner), and after this operation, only a fraction of the power is left to enter into the interferometer. Note that there is an output beam cleaner, too, not only an input cleaner.Another aspect is the "MW" might seem huge, but that is not continuous power. The number is that big because it's a very short pulse. IIRC the continuous power would be something like 200W for the LASER, not kW, not MW, but there were many upgrades over decades, both in power, in mirrors and in the detected frequency range, so the specs were quite fluid over time.The LIGO is more elaborated that it appears in either of those YT videos, pretty sure there are a lot of crucial details that are inside knowledge only, and not even mentioned. I know nothing about optics or physics (I'm an electronist who loves physics as an amateur only), only talking about the detail after searching and browsing a few PDFs last week, might have got it all wrong, so don't take as correct what I was writing. My impressions are after browsing (brief preview only, I didn't read them in full) files like these:DC readout experiment in Enhanced LIGO, Fricke et al., arXiv:1110.2815v2https://arxiv.org/pdf/1110.2815<--- has a more detailed diagram of the optical path in the LIGO detectorCommissioning the Advanced LIGO L1 Input Mode Cleanerhttps://dcc-llo.ligo.org/public/0058/T1100201/004/L1_InputModeCleanerIntegration.pdf<--- has some numbers and specs in it, to make an idea about the orders of magnitudeThese and a few more were some random PDFs that popped in the first page when searching about LIGO, no idea if they were relevant, or still valid today after so many upgrades over the years.

author: Doctorandus_P
author_rank: Super Contributor
timestamp: June 11, 2024, 12:37:18 pm
content: Quote from: charliehorse55 on June 07, 2024, 08:13:59 pmYou want to bridge 12 orders of magnitude through "iterative improvements"?That is like building a tesla coil when you need a micro volt power supply. And then you already start at the "sensitive" part of the bar and have to extend it.