Questions tagged [laser-cavity]

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Does the beam image invert on each round-trip through a hemispherical laser cavity?

When one creates a hemispherical laser cavity, using one flat and one concave mirror, does the beam image invert each time it makes a round trip? I know when passing through the focus of a lens/mirror,...
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Compensation of polarization-dependend frequency offset of a passive optical cavity

I have a passive optical cavity used as an OPO for the generation of squeezed states in pulsed regime, schematized in the following figure. The crystal used to generate squeezing is a KDP (C1), which ...
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Why some laser diodes have angled window?

Why some laser diodes have angled window? Here is an example
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Why open cavity decrease the number of oscillating modes?

Number of modes inside a cavity for laser action is proportional to the volume now if I open the sides of the cavity then volume of the cavity becomes infinite so number of mode actually increase.......
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The Stark-Lo Surdo effect

What does the Stark-Lo Surdo effect consist of in the interaction of the electromagnetic field and the active medium in a laser? I thank those who want to give a clear and concise answer. In my ...
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Reflection spectrum of a triangular cavity

I am struggling to find the expected reflection spectrum of a triangular cavity, both with and without round-trip losses. This is a simple scheme: Laser light is being coupled in the cavity through ...
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What is the transverse mode separation in a laser cavity?

I'm currently researching the intermodal distance of transverse and axial modes in optical cavities. But the equation defining the longitudinal separation contains the +- sign, does this imply that ...
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Minimising losses in an optical resonant cavity

I am doing a question and I am asked to calculate the radius of curvature of two identical mirrors at either end of an optical cavity in order to minimise the losses in the cavity. Is the correct ...
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Laser Cavity Power vs. Output Power

I think I read recently that the power inside a semiconductor’s resonator cavity can reach the megawatt level, due to the buildup of standing waves in the gain material, even though the output power ...
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Is there a connection between the differential gain and the spontaneous emission factor $\beta$ in semiconductor lasers?

The section below is from the paper G. Bjork and Y. Yamamoto, "Analysis of semiconductor microcavity lasers using rate equations," in IEEE Journal of Quantum Electronics, vol. 27, no. 11, pp....
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How are frequency combs obeying the energy conservation?

The operational principle of frequency combs is that you generate very short pulses (in time domain), and that in the frequency domain (due to Fourier's transform) the spectrum of such pulses is a ...
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SRS is reduced by increasing the bandwidth of the OC in high power fiber lasers generally. What happens if the bandwidth is increased too much?

Several articles suggest, in a MOPA configuration high power fiber laser, the SRS can be mitigated by increasing the bandwidth of the OC FBG. How to determine the optimized bandwidth of such FBG? Does ...
Chat0924's user avatar
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How many cavity round trips typically occur inside laser resonators?

Is it possible to estimate the number of cavity round trips occurring inside typical laser resonators, e.g. in a laser diode or a He-Ne laser? Motivation: I've come across a short blog text, where the ...
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How does one integrate $E^2(r)$ on $r$ to conclude that the relative power contained within $w_0$ is $1 - 1/e^2 = 0.86$ of the total beam power?

In a chapter on the basics of laser physics, my textbook says the following: The $c/2L$ spacing of resonance is typical of the so-called longitudinal modes, or $\text{TEM}_{00}$ modes, characterised ...
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Transmission spectrum of optical cavities

Why is the transmission spectrum of a Fabry-Perot (FP) cavity looks different to that of a ring resonator? i.e. at resonances in FP we have transmission peaks at resonances whereas in rings there are ...
AB 17 's user avatar
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Difference between seed and pump in chirped pulse amplifier

What is the difference between to seed an optical amplifier (such as Chirped Pulse Amplifier) and to pump it with a laser source?
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Single photon Rabi frequency for Exciton Photon in 2D potential well with microcavity

I was just going through an article on Exciton-polariton Condensate in 2D and in the photon-exciton interaction strength (single photon Rabi frequency) inside a cavity seems to have a term of Bohr ...
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What happens when bending laser light in a liquid stream smaller than its wavelenght?

When you point a laser into a water stream it bends with the waterstream and exits at the end. It bounces constantly from the "virtual wall" till it reaches the end of the stream. Now if the ...
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Purcell effect for large cavities

The model of interest is a 2-level system (e.g. an atomic transition) inside a damped single-mode cavity. The purcell effect states that the atomic decay rate inside the cavity $\Gamma_{cav}$, on ...
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Use standing wave to understand mode locked laser

Recently when I was trying to explain the principle of kerr-lens mode-locked laser, however I find that I don't even understand it myself. People around me always say the longtitude modes of the ...
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Cavity decay rate dependence on frequency

Photons inside an imperfect cavity will decay outside with a rate proportional to the peak width $\delta \omega$. A spectrum of such a cavity (with different quality factors) is shown below My ...
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In fiber wave guide we only consider transverse (TM,TE,EH) modes of laser. Why not we consider londitudenal modes?

Laser beam guiding through fiber.
jazzi mao's user avatar
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Why is a cavity's free spectral range determined by the group refractive index?

Many sources including Wikipedia and others give the free spectral range of a resonator as a function of the group refractive index $n_g$ by $$ \Delta \nu_{FSR} = \frac{c}{2 n_g L}. $$ I have a hard ...
derklaus's user avatar
2 votes
2 answers
347 views

How does one get this steady-state solution?

I am studying the concept of a "gain medium" inside a laser cavity. The active atoms are taken to have the two levels $a$ and $b$, separated by energy $\hbar \omega$ and represented by a ...
The Pointer's user avatar
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Describing intensity of electric field in laser cavity as a dimensionless quantity

I am studying the concept of a "gain medium" inside a laser cavity. The active atoms are taken to have the two levels $a$ and $b$, separated by energy $\hbar \omega$ and represented by a ...
The Pointer's user avatar
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"Loss" around the transmitting window of a laser cavity due to diffraction?

Take a laser cavity consisting of a gain medium, a totally reflecting mirror, and a partially transmitting window: (https://www.researchgate.net/figure/Laser-cavity-composed-of-a-gain-medium-in-...
The Pointer's user avatar
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Why would this integral of the time derivative of the magnetic field equal zero?

I'm reading electrodynamics physics notes that describe a 1-dimensional cavity of length $L$. The cavity is said to lie along the $z$-axis from $-L$ to $0$. There is a reflective mirror at $z = 0$, ...
The Pointer's user avatar
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1 answer
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Expansion of the derivatives of the electric and magnetic fields

I'm reading electrodynamics physics notes that describe a cavity of length $L$. The cavity is said to lie along the $z$-axis from $-L$ to $0$. The electric field is polarized in the $x$ direction and ...
The Pointer's user avatar
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Frequency Shift of the Cavity Resonance Due to the Leakage of the Cavity

I have a question regarding planar cavity (or any other cavity) resonance. From my understanding it is true that if the cavity walls are almost perfectly reflective, then the resonance frequencies ...
Andris Erglis's user avatar
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1 answer
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What is the difference between this "spectral width" and the laser linewidth (FWHM)?

I am currently looking at the 1550nm fibre-coupled DFB laser diodes on Alibaba for use in interferometry experiments. These are commonly used in optical communications applications, but it seems to me ...
The Pointer's user avatar
2 votes
2 answers
599 views

Explanation of 'modal gain' (especially in the context of laser diodes)

I have seen the phrase 'modal gain' used in the context of photonics. Researching this phrase, I found this resource, which explains it as follows: Modal Gain: which is the material gain adjusted to ...
The Pointer's user avatar
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How does diffraction cause laser beam divergence, and why will a laser beam always diverge, due to diffraction?

I have seen it said that diffraction causes laser beam divergence, or that a laser beam will always diverge, due to diffraction, or some variation of these statements. I understand diffraction in ...
The Pointer's user avatar
1 vote
1 answer
184 views

Is it true that longer laser cavities generally produce more collimated beams?

I read that longer laser cavities generally produce more collimated beams. Is this true? And, if so, then why? The closest source of information that I could find is this Wikipedia article on ...
The Pointer's user avatar
2 votes
2 answers
119 views

Why does a laser cavity being finite imply that beam divergence occurs?

I recently read that one of the reasons laser beam divergence occurs is because the radius of the cylindrical cavity is finite, and so the stimulated emission with amplification also occurs for ...
The Pointer's user avatar
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1 answer
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How is it that having a laser cavity geometry with one flat mirror and one curved mirror produces a more divergent beam?

I recently asked this question about the non-axial photons of a laser cavity. While doing further research on the subject, I read that exploiting the paraxial photons by having one mirror of the laser ...
The Pointer's user avatar
14 votes
3 answers
843 views

What happens to the non-axial photons of a laser cavity?

When a laser cavity is pumped, the axial photons are reflected back and forth by the cavity mirrors and so contribute to stimulated emission, but the non-axial photons do not have this opportunity. ...
The Pointer's user avatar
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1 answer
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There may be phase variations $\ge \lambda/4$ across the diameter of each mirror in any laser cavity?

I am currently studying the textbook Laser Systems Engineering by Keith Kasunic. Chapter 1.2.2 Spatial coherence says the following: The concepts of spatial coherence and beam quality arise because ...
The Pointer's user avatar
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Which of those two is better way of avoiding mode hopping in laser?

I'm supposed to design a laser cavity that would avoid mode hopping. I have two projects in mind, and I did some simulations. The result for relative intensity of modes (no gain spectrum in account, ...
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1 vote
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Why can no commercial laser products achieve a frequency stability of $< 1 \ \text{Hz}$?

I am currently studying the textbook Laser Systems Engineering by Keith Kasunic. Chapter 1.2.1 Temporal coherence says the following: Even a frequency-stabilized SLM laser has a linewidth – an ...
The Pointer's user avatar
5 votes
1 answer
550 views

Homogeneous gain saturation and single-longitudinal-mode lasing

I am currently studying Laser Systems Engineering by Keith Kasunic. Chapter 1.2.1 Temporal Coherence says the following: Whether or not multiple axial modes will lase depends, in part, on the cavity-...
The Pointer's user avatar
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1 answer
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If most types of practical lasers produce a large number of half-wavelengths, then how are they practical for use at all?

I am currently studying Laser Systems Engineering by Keith Kasunic. Chapter 1.2.1 Temporal Coherence says the following: Axial (or longitudinal) modes are determined by the geometrical fit (or ...
The Pointer's user avatar
2 votes
1 answer
559 views

Half-wavelengths of the electric field fit in the cavity length $L$: $m \frac{\lambda}{2n} = L$

I am currently studying Laser Systems Engineering by Keith Kasunic. Chapter 1.2.1 Temporal Coherence says the following: Axial (or longitudinal) modes are determined by the geometrical fit (or ...
The Pointer's user avatar
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342 views

What is half width of gain profile? why is it used as delta lamda while calculating number of longitudinal modes? (Correct me if wrong on this)

How many longitudinal modes can be excited for an He-Ne laser in a cavity of length 30 cm and having half width of gain profile of laser material 2 ×〖10〗^(-3) nm? The emission wavelength is 6328 Å.
All Might's user avatar
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What is the physical meaning behind negative slope of laser characteristics?

Sometimes I measure LIV curves of many semiconductor lasers with the same material and width and different cavity length. There should be positive slope and intercept of Threshold current vs inverse ...
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Q-factor in a laser cavity and second derivative

I found the following text regarding laser cavities. But I do not understand why they use the second derivate instead of the first. Since the second can take any positive or negative value.
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Proof of the paraxial law for Gaussian beams in laser design [closed]

How does one proof that the complex beam parameter $q_1$ of a Gaussian beam is altered according to $$q_2=\frac{Aq_1+B}{Cq_1+D}$$ when passing through an arbitrary optical element with a known ABCD (...
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Is the higher $Q$-factor of a laser cavity the better?

A high $Q$ cavity means that the light will travel between the cavity mirrors many times before leaving the cavity. The more times the light reflects, the longer the gain medium effectively extends. ...
LearnerAL's user avatar
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2 answers
138 views

In the end, how do I make a semiconductor laser with specific wavelength?

I know that laser wavelength depends on four important properties: Bandgap of its material Gain spectrum Length of cavity Size of a quantum well, if we talk about the quantum well laser But it's a ...
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4 votes
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Physical meaning of Cavity Finesse

I was wondering what does the term cavity finesse mean, physically? I understand that it is defined by— $$F = \frac{ \text{Free Spectral Range (FSR)}}{\text{Linewidth}},$$ where FSR is the frequency ...
HoOh the legendary chicken's user avatar
2 votes
1 answer
463 views

Light confinement in homojunction laser diode

Why is light confined to the depletion region in a simple homojunction Fabry-Perot laser diode, like the one schematically illustrated below? Does this region for some reason have a higher refractive ...
Malcolm Regan's user avatar