“Just like any complicated problem, we leave it as an exercise to the viewer”! Funnier (though very encouraging) words have rarely been spoken! Professor Ezekiel left an absolutely amazing legacy with these lectures! Thanks to the staff at MIT for making it available to us all!
When he's adjusting the mirror mount, is he increasing or decreasing the distance between the output coupler and highly reflective mirror? is he changing the the angle between the two?
I have coupled the HeNe beam to an external cavity with two mirrors, my output transverse modes continuously oscillates from lower order to higher orders, kindly explain why it is oscillating (The laser is not collimated using a lens, it is diffraction limited and is directly fed to the external cavity mirrors)
Because the power which can be amplified in higher order modes are being attenuated by the pinhole and are lost, so the power of TEM00 is low at the cost of getting the beam clean.
No, but the Free Spectral Range gets smaller (FSR = c/2L , L: mirror distance), meaning you dont have to move one mirror as much along the beam axis to see the next resonator mode.
“Just like any complicated problem, we leave it as an exercise to the viewer”! Funnier (though very encouraging) words have rarely been spoken!
Professor Ezekiel left an absolutely amazing legacy with these lectures! Thanks to the staff at MIT for making it available to us all!
Beautifully explained
I think it would be much more interesting if the physical concept of the appearance of different modes would be explaned.
When he's adjusting the mirror mount, is he increasing or decreasing the distance between the output coupler and highly reflective mirror? is he changing the the angle between the two?
I have coupled the HeNe beam to an external cavity with two mirrors, my output transverse modes continuously oscillates from lower order to higher orders, kindly explain why it is oscillating (The laser is not collimated using a lens, it is diffraction limited and is directly fed to the external cavity mirrors)
Why do the higher order modes have higher power? When I measure the 11 transverse mode, it has over double the power of the 00 mode.
Because the power which can be amplified in higher order modes are being attenuated by the pinhole and are lost, so the power of TEM00 is low at the cost of getting the beam clean.
Are the number of modes being increased, by increasing the length of the resonator?
No, but the Free Spectral Range gets smaller (FSR = c/2L , L: mirror distance), meaning you dont have to move one mirror as much along the beam axis to see the next resonator mode.
This is why i hate college.
Ryan Why? No idea.