Lasers

Содержание и основные понятия

The laser uses forced radiation: the photon triggers the appearance of a second photon of the same frequency, phase, polarization and direction.
GEF · 11 grade
PIF · Baseline
Interactive model
Compulsive radiation
Population inversion
Resonator
Coherence
01
The physical picture
What happens and what boundaries the model has.
Main message
The laser uses forced radiation: the photon triggers the appearance of a second photon of the same frequency, phase, polarization and direction.
Inverted population levels are needed for reinforcement.
The optical resonator has multiple light from the active environment.
The laser beam is monochromatic, coherent, and it's very small.
How to reason
First, name the system and the interaction, then select the values, and only then write down the law. The formula works within the model's assumptions.
02
Laws and values
Symbols should be read as a relationship of values, not as a recipe for substitution.
Δ
E
=
h
ν
\Delta E=h\nu
Δ
E
=
h
ν
transformation frequency
P
=
E
t
P=\frac{E}{t}
P
=
t
E
​
Power of beam
Review of the situation
Two resonator mirrors select directions in which the wave increases repeatedly in the active environment.
04
Links and application
In the real world
Two resonator mirrors select directions in which the wave increases repeatedly in the active environment.
Model verification
Compare the prediction with observation, evaluate the units, the order of magnitude and the influence of the factors not taken into account. Disparity does not always mean an error of law: often idealization is no longer sufficient.
C
What needs to be understood
Outcome 1
Explain the physical meaning of the theme "Lasers" through the model, not just the formula.
Outcome 2
Distinguish and correctly use terms: forced radiation, inversion of the population, resonator.
Outcome 3
Indicate the conditions for the applicability of the law, verify units and limit cases.
T
Terms of the topic
The definition should indicate the physical meaning, not a substitute for a domestic synonym.
Compulsive radiation
The release of photon by the system with the same frequency with the agreed characteristics.
Population inversion
The state of the environment where the upper energy level of the particles is larger than the lower level.
Resonator
A system that supports the fluctuations of certain own frequencies and reinforces them in response.
Coherence
The consistency of the fluctuations, where the differences in their phases remain constant or predictable.
F
Origin and conclusion of the formulas
The fundamental law cannot be "proven" by algebras: for each record, it is stated whether it is a definition, an experimental law, or a model effect.
Δ
E
=
h
ν
\Delta E=h\nu
Δ
E
=
h
ν
Postulate or Model
The frequency of transition.
The following is an indication of the definition, experience or law from which this entry arises and where it is applicable.
Δ
E
=
E
2
−
E
1
>
0
\Delta E=E_2-E_1>0
Δ
E
=
E
2
​
−
E
1
​
>
0
For the laser transition, the difference between the top and the lower energy levels is selected.
E
γ
=
h
ν
E_\gamma=h\nu
E
γ
​
=
h
ν
In the case of forced radiation, the resulting photon has the same frequency, phase and direction as the external photon.
E
γ
=
Δ
E
⇒
ν
=
Δ
E
h
E_\gamma=\Delta E\quad\Rightarrow\quad\nu=\frac{\Delta E}{h}
E
γ
​
=
Δ
E
⇒
ν
=
h
Δ
E
​
The energy retention triggers the frequency of laser radiation.
Conditions:
The transition between the two specified levels of the active environment; the increase in levels is small, ΔE is positive.
Monitoring:
The dimensions of both parts shall coincide; the result shall be checked for sign, order and limit case.
P
=
E
t
P=\frac{E}{t}
P
=
t
E
​
definition
The power of the beam.
The following is an indication of the definition, experience or law from which this entry arises and where it is applicable.
P
ср
:
=
Δ
E
Δ
t
P_{\text{ср}}:=\frac{\Delta E}{\Delta t}
P
cf
​
:=
Δ
t
Δ
E
​
The average power is defined as the energy transferred by a beam per unit of time.
E
=
N
h
ν
E=Nh\nu
E
=
N
h
ν
For N equal photons, total energy is equal to the sum of their quantum energy.
P
=
E
t
=
N
h
ν
t
P=\frac{E}{t}=\frac{Nh\nu}{t}
P
=
t
E
​
=
t
N
h
ν
​
Therefore, the power can also be linked to the number of photons passing through time t.
Conditions:
E is the energy transferred through the selected section over the interval t > 0; for the variable beam, this is the average power, not the instantaneous power.
Monitoring:
The dimensions of both parts shall coincide; the result shall be checked for sign, order and limit case.
!
Model boundaries and typical errors
Error: Forget model condition
You can't move the formula to any situation just because it's a coincidence of letters. The key condition of this topic is that you need inverse population levels to reinforce.
How to Check the Mind
The optical resonator produces multiple light on active media. Then check the units, vector direction and behaviour of the result at zero or very large parameter.
Σ
Conclusion on the topic
Lasers
The laser uses forced radiation: the photon triggers the appearance of a second photon of the same frequency, phase, polarization and direction.
Inverted population levels are needed for reinforcement.
The optical resonator has multiple light from the active environment.
Any numerical result shall be accompanied by a unit, a sign and an explanation of its physical meaning.
The content is consistent with the FRP on Physics of the OS/OSS 2025 and the subject matter of the current lines of the PNP: I. M. Peryškin and co-authors (7–9), G. J. Mäkishev and coauthors (10–11), and with the lines "Engineers of the Future" and V. A. Kasyanov. The original texts are not reproduced, the text of the textbooks is not reproduced.