outreachspeedoflight-tspspi 0.0.1a2

Simple frontend to illustrate our speed of light measurements for Wiener Forschungsfest

Outreach project utility: Speed of light

Work in progress

This is the frontend to the speed of light outreach project. This project has been developed to measure the speed of light similar to the idea that Hippolyte Fizeau developed in 1848. In contrast to his experiment in this case a little cheat is used - a bicycle works as chopper to produce a sharp difference in light intensity of a laser source. The light travels through two arms of the experiment - one being only a few meters away from the chopper, the other being about hundred meters away. The signal of both pulses is recorded on photodiodes and sampled by a fast oscilloscope (this is where the cheating comes in - we have a definition of time and fast direct sampling).

Since this project has been developed to increase the interest in science and let people participate actively during exhibitions it's by no way a precision measurement - it's more of a (working) experiment that people can look at, play with and grasp the idea of light traveling at finite speeds.

This application:

• Gathers data from the oscilloscope
• Visualizes the samples
• Calculates a cross correlation of the symmetrized periodicalized recorded function
• Estimates the speed of light from this correlation function by doing a simple peak search
• Does averaging over the estimated speed of light and visualized this.

Experimental setup

The experimental setup consists of two basic parts:

• A chopper assembly - where a bicycle is used (or any other kind of chopper)
• A beamsplitter and photodiode assembly as well as a long beamline

Example screenshots

Running the embedded DAQ simulation

Configuration files

daq.conf

{
	"osci" : {
		"ip" : "10.0.0.196",
		"port" : 5555,
		"sperdiv" : 1e-6,
		"trigch" : 1,
		"triglvl" : 0.5,
		"ch1" : {
			"offset" : 0,
			"scale" : 0.5
		},
		"ch2" : {
			"offset" : 0,
			"scale" : 0.1
		}
	},
	"chopper" : {
		"diameter" : 68e-2
	},
	"path" : {
		"length" : 100,
		"n" : 1.4
	},
	"loglevel" : "debug",
	"mode" : "continuous"
}

• Mode can be triggered or continuous
• IP of oscilloscope has to be present
• Seconds per division, trigger channel, trigger level as well as scale and offset per channel are optional

gui.conf

{
	"loglevel" : "debug",
	"lastsamples" : 32,
	"averagecount" : 16,
	"plotsize" : {
		"x" : 460,
		"y" : 260
	},
	"mainwindowsize" : {
		"x" : 1300,
		"y" : 800
	}
}