Questions tagged [laser]

Light Amplification by Stimulated Emission of Radiation. A means of creating coherent light by either driving an atomic or molecular transition in an optical cavity or firing a beam of electrons through an undulator.

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What is a 'delta function optical pulse'?

What is a 'delta function optical pulse'? I suspect this means that the optical pulse can be modelled as having the properties of the Dirac delta function, but then what does it mean to say that an ...
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Do ionization energies of atoms change when they are in a moving reference frame

I understand that special relativity says if I hold a ruler in my own inertial-reference frame, then if a ruler moving relative to me passes me, that I will see the moving ruler as shorter than the ...
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Will any orange-tinted window offer protection against 450nm laser? [closed]

Violet diode lasers in the wavelength of about 450nm have gained widespread usage among enthusiasts of DIY; one potential risk of lasers is eye damage; goggles and enclosures with special tinted glass ...
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Why do artificial transmissions of coherent EM waves tend to be isotropic at radio frequencies but directional at visible frequencies?

This is a somewhat soft question, and I'm far from an expert on the subject, so it's possible that my premise is factually incorrect. The practical generation mechanisms for useful real-world coherent ...
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Is lasing possible in a 2 level atom if the energy levels are degenerate?

When introduced to laser physics we use Einstein Coefficients: $A_{21}$ = rate of spontaneous emission $B_{21}$ = rate of stimulated emission $B_{12}$ = rate of stimulated absorption A standard ...
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Setting up Twyman-Green interferometer

I am trying to reproduce some experiments for multiple degree of freedom homodyne interferometry, but I am struggling to understand the basics of the hardware I need. The literature I am referring to ...
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What is the relation between FWHM and bandwidth of laser? [closed]

Is bandwidth and FWHM of a laser source the same? For a laser of 5GHz, 1550.92 nm, and 43ps FWHM what is the bandwidth?
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What is the Laser linewidth and why do we measure it? [closed]

What is the Laser diode line-width and why do we measure it? what important information about the LD does it provide or allow us to infer from it?
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How does the ladder excitation of electrons lead to transparency (EIT)?

I'm trying to understand the ladder transition in the Electronically Induced Transparency (EIT) process. I know that to eliminate the effect of a medium on a propagating beam, the electrons must be ...
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Modeling Gaussian Beam Focusing

I am trying to model beam focusing using machine learning algorithms in Python with the goal of building a model that learns to focus the beam to the smallest point possible. However, I am lost as to ...
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Could someone contrast a “Single-pulse” laser to a CW and Pulsed laser (8 times in a second)

I'm hoping someone could provide the difference between a single-ulsed laser to a CW laser or a pulsed laser (>.25s for a pulse length).
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Spectrum of laser light absorbed and re-emitted by a white object

If I shine a red laser onto a white surface, I assume that: some of the red light will be nearly instantly reflected, some will be absorbed and converted into phonons and some will be absorbed and re-...
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What is the highest repetition rate achieved for Terawatt and Petawatt-order lasers?

What is the highest repetition rate achieved for Terawatt and Petawatt-order lasers? respectively. Source would be appreciated.
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Obtain clear fringes from interferometer

I have just begun setting up an interferometer to take some measurements. I am trying to reproduce one paper I found in literature for 3 DoF homodyne interferometry. The detector is merly a CMOS ...
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Is there any equation to determine the waste heat produced in a pulsed laser system?

By waste heat I mean how much the laser system would heat itself (and therefore it would be necessary to cool it down). Simple equations are appreciated.
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Laser Physics: Question Concerning SPAD

In a Laser Physics lecture, we had had the following Figure for a SPAD (a single photon APD): The reasons for which the detection efficiency, which is plotted on the y-axis, goes down as a function of ...
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Are 'Terahertz-pulse lasers', like, 'Terahertz time-domain spectroscopy' and such, of Terahertz-frequency or trillion-pulses-per-second?

From Phys.org: Light-controlled Higgs modes found in superconductors; potential sensor, computing uses. The mode can be accessed and controlled by laser light flashing on the superconductor at ...
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Definition of far field for gaussian laser beam

I've been looking for the definition of far field for a gaussian laser beam. However, most sources that I've seen just say something on the lines of "where the distance from the focus is much ...
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How to make a line with a laser pointer

So I was going through a meandering "thought journey" and was thinking about human's persistence of vision. This can be demonstrated by rapidly moving a laser pointer back and forth, which ...
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How does stimulated emission occur in 3 level lasers?

My understanding is that in 3-level lasers, we pump up a collection of atoms from the ground state of energy $E_1$ to some excited state $E_3$ with the help of monochromatic radiation of Energy $E_3-...
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Effect of saturated beam laser on transmission in solid materials

The transmission measurement setup commonly features a source (e.g. laser), steering mirrors, an integrating sphere, coupled to a power meter (or spectrometer). For a solid sample placed between the ...
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Why are there no solid-state blue lasers?

Why are there no viable solid state gain media that directly lase in the visible spectrum? With the exception of ruby used in the first laser (red), all of the bulk gain materials like Nd:YAG and ...
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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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Why can't lasers cut shiny surface and reflect?

A laser can cut hard material but why it reflects and don't cut the shiny surface for e.g. a mirror. Shouldn't it cut a mirror also as it is powerful and cuts hard substances.
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What does the L-rating on laser goggles stand for?

I know how the LB-rating works, but I recently found some older goggles which are rated like this: 500-600 DIR L2. For all other goggles I have seen so far they would write LB2, not just L2.
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Are Field Beams Possible?

I was recently wondering why the field force between two objects is proportional to the square root of the distance (sometime you just take things for granted). This comes from the inverse-square law, ...
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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 ...
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Why is laser light described by a coherent state?

This is a follow-up to this recent answer by Wouter to this related question from 2015, and a comment by Emilio Pisanty underneath. I have read the papers by Mølmer, Bartlett et al., Wiseman, and ...
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How to compare operational condition of solar cells investigated with pulsed and CW lasers?

my question is related to the fact that many measurements require CW laser to excite a solar cell material and others need a pulsed laser to investigate their properties in time. Usually for solar ...
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Reflection, Transmission and Absorption Behaviour of 3C-SiC over Temperature

When plotting the percentage of transmitted, reflected and absorbed laser power over the incident laser power on a 3C-SiC (200nm thick) sample, I measured that transmission stays almost constant, ...
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Self-focusing of laser beam

I have exam of „Nonlinear Optics“ tomorrow and I don't understand one thing. In the book it is said, that self-focusing occurs when power of beam reaches so called critical focusing power $P_{cr}≈\...
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What is the waist radius of a gaussian beam after passing through lenses with different numerical apertures?

I have a question regarding gaussian beams and lenses. If a collimated gaussian beam hits a lens with a certain numerical aperture ($\mathrm{NA}$), we can calculate the beam waist in the focus by $\...
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What parameters limit the speed of LASER operation

What parameters limit the speed of LASER operation and how can we overcome them to obtain ultrafast laser sources.
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How to increase recombination lifetime in LASER?

In a semiconductor laser, the light emission happens due to recombination in a pn junction. But the recombination lifetime in a pn junction is very small as a result of which the charge carriers do ...
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How to increase laser output?

In a semiconductor laser, light is emitted from the pn junction and guided across the laser length to come out from the mirrors. During this travel across the length of laser, the photons enter the p-...
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Apart from mirrors, what other feedback mechanisms can you think of in a semiconductor laser

Today, I was asked by my professor this question. I was unable to answer it but I am curious to know about this. Apart from mirrors, what other feedback mechanisms can you think of in a semiconductor ...
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How does the Kerr focusing effect leads modelocking?

I read about the Kerr effect in a medium like a Ti:sapphire focuses the Gaussian beam by acting like a virtual lens. That is fine. But here is my confusion. Inside the cavity when the laser beam is ...
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How to increase laser efficiency and decrease photon loss into the P and N layers?

So, I reading about lasers. We use mirrors to use the same photons to initiate the stimulated recombination. For this, we use mirrors. Mirror (Very Highly reflective) | - Diode - | Mirror (Highly ...
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Theoretical efficiency of a laser

A laser produces a coherent, collimated light beam. This is like a less-disordered version of the light from say a light bulb. When I learned about heat pumps in thermodynamics class, I found that we ...
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Area of detectable optical transmission as a function of distance in the context of SETI

The relevant page on SETI's official website states: The SETI Institute, along with scientists from the University of California's Lick Observatory, UC Santa Cruz, and UC Berkeley has coupled the ...
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Confused about Rabi oscillations method

I am a bit confused about how the Rabi oscillations method is applied in practice. The probability of producing a transition (assuming the atoms start in the ground state and we ignore the lifetime of ...
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Laser beam visibility in atmosphere

I'm working on a science fiction story and would like to introduce lasers as a weapon. I've read a bit about the effect of very high energy breams in air and it is hard to get a definitive story. With ...
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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-...
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The frequency spread of a wavepacket from a femtosecond laser pulse

I want to ask a question about the frequency spread of a wavepacket from a femtosecond laser pulse. I was presented with the following question today: Compute the frequency spread of a wavepacket ...
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Laser beam segmentation

I want to point out that I have almost no knowledge in light and similar topics in physics, so this may sound like a weird question. I was wondering if it's possible to make a laser beam appear ...
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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 ...
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Creating Different Colours From A Pulsed Monochromatic Light Source

I am currently learning about fibre optic communications, which I understand use pulsed laser sources to generate a "bitstream" to send through the fibre using some form of pulse width ...
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Practical books about lasers

Can someone point me towards some good books about laser from a practical/experimental perspective (maybe even a review paper). Most books I found spend a lot of time going through derivations and ...
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Excitation of $n$ inhomogenous two-level atom with different detunings? Bloch sphere

I am learning about the bloch sphere and how it is used to to in two level systems. I have done some research already but I am slightly confused. Suppose you have an $n$ number of inhomogenous atoms ...
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Relationship between Intensity of a beam, energy, FWHM in time domain and FWHM of the transverse intensity distribution

Suppose I have a laser pulse whose intensity, energy and FWHM in the time domain I know is there a way to use this information to calculate its FWHM beam waist using this information. Thanks.

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