Posts tagged ‘TOF’

Direct Measurement of the Speed of Light using a Cheap Laser Diode – II

In my previous blog post, I discussed the basic TOF method for direct measurement of the speed of the light. In order to measure the time of flight accurately, we need to be able to both generate and detect very fast rising signals. One way to generate a fast rising, short duration laser beam is via an avalanche pulse generator as we discussed previously. In this blog post, we will take a look at the receiver end and conduct some experiments. A video of the experiment is included towards the end. Continue reading ‘Direct Measurement of the Speed of Light using a Cheap Laser Diode – II’ »

Direct Measurement of the Speed of Light using a Cheap Laser Diode – I

Speed of light c in air can be measured either directly or indirectly. There are many ways to infer c with indirect measurements. For instance, we can measure the propagation delay of a signal through a coaxial cable (or an optical fiber) using the TDR analysis. With the length of the coax or optical fiber known, the speed of light can be calculated using the known velocity factor (or the refractive index of the fiber) and the measured propagation delay. Another example of indirect measurement is to measure the wavelength of a known frequency standing wave (e.g. a microwave signal) and derive the phase velocity of the electromagnetic wave in air. Continue reading ‘Direct Measurement of the Speed of Light using a Cheap Laser Diode – I’ »