Measure Phase velocity/group velocity of EM-wave


by spookyfw
Tags: emwave, measure, phase, velocity, velocity or group
spookyfw
spookyfw is offline
#1
Jul23-12, 03:19 AM
P: 24
Hey folks,

some weeks ago we had an trial-exam and one of the questions there was: "How do you measure phase and group velocity."

That question really got me. Having a fastly oscillating wave as carrier and then the envelope. Can someone help me? Is it impossible for the phase, as it is usually a harmonic one?

Would be really great if someone would know the answer,
take care,
spookyfw
Phys.Org News Partner Physics news on Phys.org
Physicists design quantum switches which can be activated by single photons
'Dressed' laser aimed at clouds may be key to inducing rain, lightning
Higher-order nonlinear optical processes observed using the SACLA X-ray free-electron laser
f95toli
f95toli is online now
#2
Jul23-12, 06:47 AM
Sci Advisor
PF Gold
f95toli's Avatar
P: 2,197
I am assuming you are talking about EM signals.
How you do it depends on the frequency range. For RF/Microwave you can use a phase detector, these are either dedicated components that you can buy; or you use a saturated mixer.
spookyfw
spookyfw is offline
#3
Aug22-12, 01:27 AM
P: 24
Sorry for this very late reply. First of all: thank you very much for your answer. Yes, I was talking about EM-waves. More about a pulse in the visible region though. I wondered how one would then discriminate and measure phase and group velocity. Using a phase detector sounds reasonable, but how does it work?

Would be really grateful if someone would know :).

PhilDSP
PhilDSP is offline
#4
Aug22-12, 03:22 AM
P: 561

Measure Phase velocity/group velocity of EM-wave


Hi spookyfw,

Except in very special circumstances, measurement of phase velocity is not feasible for a number of reasons:

1. The surface that represents the constant phase of the entire wave packet may not necessarily be a plane.

2. That surface may not necessarily travel in the same direction as the wave.

3. The amplitude of the wave on that surface may be extremely small.

4. That surface may lie outside of the causal influence of the wave.


Register to reply

Related Discussions
EM Group velocity & phase velocity in dispersive medium Classical Physics 5
wave phase velocity vs. group velocity? General Physics 0
What's the truth about phase velocity vs. group velocity? Classical Physics 3
Group and Phase velocity of wave packet Introductory Physics Homework 4
Need some help regarding phase and group velocity of a wave General Physics 2