Lec 08 Flashcards

Question

What is the energy density of radiation at frequency ν denoted by?

Answer 1

u(ν) ## Footnote This term is used in calculating the number of photons absorbed or emitted.

Answer 2

It determines the energy of photons that can be absorbed or emitted ## Footnote For example, GaP has a gap of 2.2 eV corresponding to a green photon.

Answer 3

The atom may absorb the photon and jump to a higher energy state ## Footnote This process is called stimulated absorption.

Answer 4

It is promoted to a higher energy level and is described as being 'excited' ## Footnote This transition is quantized and requires specific energy amounts.

Answer 5

Stimulated absorption, spontaneous emission, stimulated emission ## Footnote These processes explain how atoms interact with photons.

Answer 6

An atom in a lower level absorbs a photon of frequency hν and moves to an upper level ## Footnote This process increases the energy of the atom.

Answer 7

An atom in an upper level decays spontaneously to the lower level and emits a photon of frequency hν ## Footnote The emitted photon has a random direction and phase.

Answer 8

An electron in an atom goes from a lower to a higher energy level ## Footnote This changes the internal momentum of the electron and its internal quantum numbers.

Answer 9

1.9 to 3.1 eV ## Footnote These energies correspond to visible light.

Answer 10

1.96 eV ## Footnote This energy gap corresponds with the energy of red photons of wavelength 632.8 nm.

Answer 11

The minimum energy required to move an electron from the valence band to the conduction band in a material ## Footnote In neon atoms, this gap is 1.96 eV.

Answer 12

Its energy increases and it goes to the excited state E_2 ## Footnote This process is called absorption.

Answer 13

The minimum energy state and the most stable state ## Footnote Atoms prefer to be in this state when not excited.

Answer 14

An incident photon causes an upper level atom to decay, emitting a stimulated photon whose properties are identical to those of the incident photon ## Footnote This process amplifies the radiation.

Answer 15

This kind of radiation only occurs if an incident photon is present ## Footnote The emitted photon shares similarities with the incident photon.

Answer 16

The transition probability of induced emission ## Footnote This indicates a relationship between two fundamental processes in quantum mechanics.

Answer 17

The ratio of Einstein’s A coefficient of spontaneous emission and Einstein’s B coefficient of induced emission is proportional to ν³ ## Footnote ν represents frequency.

Answer 18

When the initial source of energy for spontaneous emission is supplied optically ## Footnote This is one of several types of luminescence.

Answer 19

The process where the initial form of energy is supplied by a chemical reaction ## Footnote Commonly seen in glow sticks.

Answer 20

The process where the initial form of energy is supplied by a voltage ## Footnote Used in devices like LEDs.

Answer 21

The process where the initial form of energy is caused by sound waves ## Footnote This phenomenon involves the emission of short bursts of light from imploding bubbles in a liquid.

Answer 22

The process where the initial form of energy is due to accelerated electrons hitting a target ## Footnote Often observed in cathode ray tubes.

Answer 23

Spontaneous emission that occurs in a living organism ## Footnote Examples include fireflies and certain types of jellyfish.

Answer 24

Some electrons in atoms are thermally excited to energy levels above the ground state ## Footnote This leads to spontaneous emission as they decay.

Answer 25

The process by which any object at a temperature above absolute zero naturally emits photons by spontaneous emission ## Footnote This is a fundamental concept in thermal physics.

Answer 26

Max Planck ## Footnote His work laid the foundation for quantum mechanics.

Answer 27

u in units J⋅s/m³ ## Footnote This quantity is crucial for understanding blackbody radiation.

Answer 28

The second term in the formula for spectral energy density ## Footnote It is related to the energy distribution of photons.

Answer 29

The bandwidth depends on temperature ## Footnote Higher temperatures lead to a broader range of emitted wavelengths.

Answer 30

An energy conversion process in which an excited electron or molecule decays to a lower energy level and emits a photon ## Footnote This process occurs naturally without external influence.

Answer 31

The average time for decay by spontaneous emission ## Footnote This can vary from nanoseconds to seconds depending on the material.

Answer 32

The photon may be absorbed, exciting an electron of a neon atom to a higher energy level ## Footnote Photons of smaller energy would not be absorbed.

Answer 33

When an electron in an excited state emits a second photon of the same frequency, phase, and direction upon interaction with an incident photon ## Footnote This process is essential for laser operation.

Answer 34

The number of atoms in different energy states at thermal equilibrium ## Footnote This distribution helps predict the behavior of particles in thermally active systems.

Answer 35

More excited-state atoms than ground-state atoms ## Footnote This condition is crucial for achieving laser action.

Answer 36

* Stimulated absorption * Spontaneous emission * Stimulated emission ## Footnote These processes must be balanced to produce effective laser light.

Answer 37

The total number of photons absorbed per second equals the total number of photons emitted per second ## Footnote This condition is vital for maintaining steady-state conditions in lasers.

Answer 38

The probability of spontaneous emission per unit time ## Footnote It quantifies how often spontaneous emission occurs.

Answer 39

The probability of absorption of energy per unit time ## Footnote It is crucial for understanding how materials interact with light.

Answer 40