What is Laser cavity: Definition and 13 Discussions

An optical cavity, resonating cavity or optical resonator is an arrangement of mirrors that forms a standing wave cavity resonator for light waves. Optical cavities are a major component of lasers, surrounding the gain medium and providing feedback of the laser light. They are also used in optical parametric oscillators and some interferometers. Light confined in the cavity reflects multiple times, producing standing waves for certain resonance frequencies. The standing wave patterns produced are called modes; longitudinal modes differ only in frequency while transverse modes differ for different frequencies and have different intensity patterns across the cross-section of the beam.

Different resonator types are distinguished by the focal lengths of the two mirrors and the distance between them. Flat mirrors are not often used because of the difficulty of aligning them to the needed precision. The geometry (resonator type) must be chosen so that the beam remains stable, i.e. the size of the beam does not continually grow with multiple reflections. Resonator types are also designed to meet other criteria such as minimum beam waist or having no focal point (and therefore intense light at that point) inside the cavity.
Optical cavities are designed to have a large Q factor; a beam will reflect a very large number of times with little attenuation. Therefore, the frequency line width of the beam is very small indeed compared to the frequency of the laser.

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  1. Daniel Petka

    I Does a Fabry Perot cavity charge in discrete steps?

    I'm trying to understand the Fabry Perot interferometer and came across this amazing video. Basically it all comes down to adding E-fields together with each of them being delayed by the cavity round trip time. In the extreme case, either they all interfere constructively at the second mirror...
  2. sol47739

    A Cause of spontaneous emission?

    I am reading this chapter 3 from the book called The Quantum Vacuum by P.Milonni.(Attached in the pdf, look at chapter 3.2 Spontaneous emission)There they say that spontaneous emission is due to both quantum fluctuations and radiation reaction. They say the transitions induced by the quantum...
  3. V

    How Can I Calculate the Number of Photons in a Laser Cavity?

    Homework Statement The laser cavity is formed by two mirrors separated by 15 cm. One of the mirrors has an ultra-high reflectivity and the output mirror has the much lower reflectivity of 99.5 %. How many photons are there in the cavity?[/B] The power of the laser is 1mW and the wavelength is...
  4. B

    Relation of laser pulse length and the Output Coupler trasmissivity

    Dear all, I'm within my Ph.D. studies in laser engineering and most of the details are rather new to me. Working on short pulse systems, my advisor told me some times about the relation of the output coupler transmissivity and the outcoupled pulse length, but more as a rule of thumb. According...
  5. H

    Number of Photons inside a Laser Cavity

    << Mentor Note -- thread moved from the technical forums, so no Homework Help Template is shown >> Let's say you have a laser cavity with two mirrors at either end, one is considered 100% reflective, the other 99.9%, so that a wave beam is emitted through this lower reflectivity mirror. I know...
  6. T

    Gain of active semiconductor gain medium

    Homework Statement Homework Equations γ=α+(1/2L)ln(1/Γ1Γ2) where gamma is gain, alpha is absorption constant, and Γ are reflection coefficients. The Attempt at a Solution I'm a little stuck on how to start. If there was no semiconductor gain medium in the cavity then I could just use the...
  7. Daniel Petka

    B Quantum Tunneling and Heat Distribution in Laser Cavities?

    What if I replaced the half transparent mirror in a laser cavity with a 100% reflective mirror? -would all photons escape due to the quantum tunneling effect? -would the mirrors melt? Thanks :biggrin:
  8. P

    What is the Q value for a krypton laser with given specifications?

    Homework Statement Calculate the Q value for a krypton laser with λ=0.569 microns, 0.568m cavity and mirror reflectance of 100% for the rear and 52% for the output window. Homework Equations For a laser cavity=> Q=(4πL)/(λ(1-R1*R2)) The Attempt at a Solution Q= (4*π*...
  9. A

    Solving Maxwell's Equations in Laser Cavity | Tips and Troubleshooting

    Hello guys, I've been trying to solve Maxwell's Equations in a laser cavity, with length L. However I cannot... I've searched over the net to find a proper solution but I couldn't. I started by taking a field E(x,y,x,t)=E0 e(x,y)e-jw te-jb z. I take the phasor E(x,y,z)=e(x,y)e-jb z and...
  10. A

    Fraction of stimulated photons that escape from a laser cavity

    How to calculate the fraction of stimulated photons that escape from a laser cavity with alpha=0.1 cm^-1 length of cavity=1mm refractive index of laser cavity=3.2 the photons are assumed to be escaping into air so approx refractive index is 1. Im assuming that alpha is some sort of...
  11. Phrak

    Understanding Energy Partition in Laser Cavity: Molecules vs. Radiation

    A laser cavity consists of a couple mirrors, a bunch of metastable molecules and some radiation. What's the partition of energy between molecules and radiation at equilibrium?
  12. B

    Is This Method for Laser Cavity Length Calculation Accurate?

    Hi, So I have a lab question for which I have to drive a formula to find the optical cavity length of a laser, L . I have results from testing the fringe patterns when I move one of the mirrors in a Michelson interferometer. It shows the typical \frac{\sin x}{x} pattern. To find the cavity...
  13. N

    Gain saturation in laser cavity

    Im studying gain saturation for homogeneous and inhomogeneously broaded transitions. Im a little confused bout the logistics of laser operation regarding the gain in the cavity. So from ground state, the atoms are optically pumped to produce population inversion(4 level system) where...