30.5 Applications of Atomic Excitations and De-Excitations
The double-helix structure of DNA was discovered in 1953 by an international team of scientists working at the Cavendish Laboratory.
They were the first to discern the structure of DNA using x-ray data.
The 1962 Nobel Prize in Physiology or Medicine was awarded to Crick, Wilkins, and Watson.
There is a lot of debate over whether or not Rosalind Franklin was included in the prize.
The figure shows a pattern of x rays in a crystal.
x-ray crystallography is a process that gives information about crystal structure, and it was the type of data that Rosalind Franklin supplied to Crick for DNA.
x rays give information on the atomic arrangements in materials and confirm the size and shape of atoms.
Current research in high-temperature superconductors involves complex materials whose lattice arrangements are crucial to obtaining a superconducting material.
x-ray crystallography can be used to study these.
The interference pattern was created by the X-ray diffraction from the hen egg lysozyme.
The German Max von Laue convinced two of his colleagues to scatter x rays from crystals after he discovered x rays in 1895.
If a pattern of waves is obtained, the x rays could be determined.
Von Laue was awarded the 1914 Nobel Prize in physics for suggesting that x rays are waves.
The father and son team of Sir William Henry Bragg and his son Sir William Lawrence Bragg were awarded a joint Nobel Prize in 1915 for inventing the x-ray analyzer.
After graduating from mathematics, the elder Bragg moved to Australia.
He studied physics and chemistry at the University of Adelaide.
The younger Bragg was born in Australia but went back to England to work in x-ray and neutron crystallography, and he supported the work of James Crick and Max Perutz for their work on unraveling the mysteries of DNA.
This time, we see the enabling nature of physics--establishing instruments and designing experiments as well as solving mysteries in the biomedical sciences.
Other uses for x rays will be studied later in the chapter.
X rays have an effect on cell reproduction and are useful in the treatment of cancer.
X rays from outer space can be used to determine the nature of their sources, such as black holes.
x rays can be used to detect atmospheric tests of nuclear weapons.
X rays can cause the fluoresce of atoms, which makes them a valuable analytical tool in a range of fields from art to archaeology.
The properties of matter and phenomena in nature are related to atomic energy levels.
The transparency of air, the color of a rose, and the output of a laser are a few examples.
It may not seem like they have much in common, but glow-in-the-dark pajamas and lasers are different applications of atomic de-excitations.
Light from a laser is based on atomic de-excitation.
The color of a material is determined by the ability of its atoms to absorb certain wavelengths.
The levels of the lycopene's atoms are separated by a variety of energies, which correspond to all visible photon energies except red.
Another example is air.
It is transparent because there are few energy levels visible to the naked eye.
The light cannot be absorbed.
The visible light is scattered weakly by the air because the visible wavelength is larger than the air atoms.
To cause red sunsets and blue skies, light must pass through kilometers of air.
The atomic energy levels of a material are related to its ability to emit light.
Some rocks glow in black light because of their mineral composition.
Posters with black lights make them glow.
When illuminated by a black light, objects glow in the visible spectrum.
Emissions are related to the mineral's energy levels.
In the case of scorpions, the blue glow is due to the presence of proteins near the surface of their skin.
This is a colorful example of fluorescent activity in which de-excitation occurs in the form of visible light.
An atom is excited to a level several steps above its ground state by the absorption of a relatively high-energy UV photon.
One way the atom can de-excite is to re-emit a photon of the same energy as excited it, a single step back to the ground state.
Smaller steps in which lower-energy (longer wavelength) photons are emitted are all other paths of de-excitation.
There are many types of energy input.
The use of fluorescent paint, dyes, and soap in clothes makes the colors look brighter in the sun.
X rays can be used to make visible images.
Neon lights and gasdischarge tubes that produce atomic and molecular spectrum can be caused by electric discharges.
Atomic emissions from mercury atoms are caused by an electric discharge in mercury vapor.
The inside of a fluorescent light is coated with a fluorescent material that emits visible light over a broad spectrum of wavelength.
The fluorescent lights are four times more efficient in converting electrical energy into visible light than the incandescent lights are.
The atom is excited by the UV photon.
It can de-excite in a single step, re-emitting a photon of the same energy, or in several steps.
If the atom de-excites in smaller steps, it will emit different energy than if it excited it.
UV, x-rays, and electrical discharge are some of the energy inputs that can causeescence.
glow-worms can be found in the Waitomo caves on New Zealand's North Island.
The glow-worms hang up to 70 silk threads each to catch prey that fly towards them in the dark.
The process of turning energy into light is very efficient.
There are many uses for florescence.
It is used to follow a molecule in a cell.
One can study the structure of genes.
The emission of visible light is observed when the molecule is illuminated with UV light and tagged with fluorescent dyes.
Identification of elements within a sample can be done this way.
The fluorescent dye shown in Figure 30.32 is called fluorescein.
Figure 30.33 shows the dispersion of a fluorescent dye in water.
The dye is used in the laboratory.
A beaker of water has fluorescent powder added to it.
Under ultraviolet light, the mixture gives off a bright glow.
These are small single-crystal molecules.
The indicators are small and provide improved brightness.
All colors can be excited with the same wavelength.
Conventional phosphors have a longer lifetime than organic dyes.
They are an excellent tool for long-term studies of cells.
Chicken cells are being imaged using a fluorescent dye.
Cell nuclei are blue while neurofilaments are green.
Spontaneous de-excitation has a very short lifetime.
Some levels have lifetimes of up to minutes or even hours.
The energy levels are slow in de-exciting because their quantum numbers are different from the lower levels.
phosphorescent substances are used to make glow-in-the-dark materials, such as Luminous dial on some watches and clocks and on children's toys and pajamas.
The stored energy is released partially as visible light when the atoms or molecules decay slowly.
After the ceramic has cooled from its firing, atomic energy can be frozen in.
Since the release is slow, thermoluminescence can be used to date antiquities.
The older the ceramic, the less light it emits.
The Chinese ceramic figure can be stimulated to de-excite and emit radiation by heating a sample of the ceramic, a process called thermoluminescence.
Since the slowly states de-excite over centuries, the amount of thermoluminescence decreases with age, making it possible to use this effect to date and authenticate antiquities.
The figure is from the 11th century.
Today's lasers are commonplace.
Lasers are used to read bar codes at stores and libraries, laser shows are staged for entertainment, laser printers produce high-quality images at a relatively low cost, and lasers send large numbers of telephone messages through optical fibers.
Lasers are used in a number of things, including surveying, weapons guidance, tumor eradication, and for reading music CDs and computer CD-ROMs.
The answer is that lasers emit single-wavelength EM radiation that is very coherent.
Laser output can be more precisely manipulated than other sources.
Laser output is so pure and coherent because of how it is produced, which depends on a metastable state in the lasing material.
electrons are raised to all possible levels when energy is put into a large collection of atoms The electrons that originally excited the metastable state and those that fell into it from above are included.
A population inversion has been achieved if a majority of electrons are in the metastable state.
An electron falls from the metastable state.
A second photon of the same wavelength and phase with the first is emitted when this photon finds another atom in the metastable state.
An excited atom with an electron in an energy orbit higher than normal releases a photon of a specific Frequency when the electron drops back to a lower energy orbit.
If this photon strikes another electron in the same high-energy space, another photon of the same frequency is released.
The emitted and triggering photons are both in the same phase and travel in the same direction.
A majority of atoms must be in the metastable state to produce energy because the probability of absorption of a photon is the same as the probability of stimulated emission.
Einstein was the first to realize that stimulated emission and absorption are equally probable.
The laser acts as a temporary energy storage device that produces a massive energy output.
One atom in the metastable state spontaneously decays to a lower level, producing a photon that stimulates another atom to de-excite.
The second photon is in phase with the first and has the same energy and wavelength.
The emission of other photons is stimulated by both of them.
A net production is necessary for there to be a net absorption.
The process was developed after advances in quantum physics.
The development of lasers was one of the reasons why the Soviet Union and the United States won a joint Nobel Prize in 1964.
Arthur Schawlow won the 1981 Nobel Prize for his work in laser applications.
The devices were called masers because they produced microwaves.
T. Maiman created the first working laser in 1960.
The red light was produced by using a flash lamp and a rod.
The name laser is used for all of the devices that produce a variety of wavelengths.
In a process called optical pumping, energy input can come from a flash tube, electrical discharge, or other source.
A large percentage of the original pumping energy is dissipated in other forms.
Mirrors can be used to enhance stimulated emission by multiple passes of the radiation back and forth.
Some of the light can be seen through one of the mirrors.
A laser's output is 1% of the light passing back and forth in a laser.
Laser construction uses a method of pumping energy into the lasing material.
Many types of lasing materials are used to make lasers.
The existence of a metastable state or phosphorescent material is what determines lasers.
Some lasers produce continuous output while others are short-lived.
The more common lasers produce something on the order of.
The red light that comes from the laser is very common.
The number of atoms of helium is ten times greater than the number of neon atoms.
The first excited state of helium stores energy.
Neon atoms have an excited state that is nearly the same as that in helium, which makes it easy to transfer this energy.
The neon state that produces the laser output is also metastable.
There are so many more helium atoms in neon that it can produce a population inversion.
The population can be maintained even while lasing occurs because helium-neon lasers have continuous output.
The most common lasers in use today are made of Silicon.
The energy is pumped into the material by passing a current into the device.
Light bounces back and forth and a tiny fraction emerges as laser light thanks to special coating on the ends and fine cleavings of the material.
The lasers can produce outputs in the range of a few hundredths of a watt.
The gas mixture has more neon atoms than helium.
In a collision, excited helium atoms can de-excite by transferring energy to neon.
Neon allows lasing by the neon to occur.
There are many uses of lasers.
Lasers can focus on a small spot.
They have a wavelength that is defined.
There are many types of lasers that provide the same wavelength of light.
One needs to be able to pick a wavelength that will be preferentially absorbed by the material of interest.
The objects appear a certain color because they absorb all other colors.
The wavelength absorbed depends on the energy spacing between the electrons in the molecule.
Unlike the hydrogen atom, biologicalmolecules are complex and have a variety of absorption lines.
In the selection of a laser with the appropriate wavelength, these can be determined.
Water absorbs light in the UV and IR regions.
hemoglobin absorbs most of the UV light.
Laser surgery uses a wavelength that is absorbed by the tissue it is focused upon.
Total loss of vision can be caused by a detached retina.
scar tissue that can hold the retina in place, salvaged the patient's vision after Burns made by a laser focused to a small spot on the retina.
Refractive dispersion of different wavelength light sources can't be focused as precisely as a laser.
Laser surgery in the form of cutting or burning away tissue is more accurate because the laser output can be very precisely focused and is preferentially absorbed.
Depending on what part of the eye needs repair, the appropriate type of laser can be selected.
The repair of tears in the eye can be done with a green laser.
The light absorbed by tissues containing blood can be used to "weld" the tear.
A laser is used to focus on a small spot on the retina, causing scar tissue to hold it in place.
The light is focused by the lens of the eye and the laser is brought to the eye.
Lasers are being used in dentistry.
The soft tissue of the mouth is the most common place where lasers are used.
They can be used to heal wounds.
The erbium YAG laser is used to cut into bones and teeth.
Since lasers can produce very high power in short bursts, they can be used to focus a lot of energy on a small glass sphere.
The incident energy increases the fuel temperature so that fusion can occur and it also increases the density of the fuel.
The implosion is caused by the impinging laser.
Nuclear fusion can be achieved using a system of lasers.
A burst of energy is focused on a small fuel pellet, which is imploded to the high density and temperature needed to make the fusion reaction proceed.
CDs and DVDs have larger storage capacities than vinyl records.
The encyclopedia can be stored on a single CD.
The CD can be used to record digital information because the pits are very small.
They are read by having a cheap solid-state laser beam scatter from pits as the CD spins, revealing their digital pattern and the information on them.
Laser-created pits on a CD's surface hold digital information.
The laser light scattered from the pit can be read.
The precision of the laser makes it possible for large information capacity.
holograms are used for amusement, decoration on novelty items and magazine covers, security on credit cards and driver's licenses, and for serious three-dimensional information storage.
When viewed from different angles, a hologram is a true three-dimensional image.
Holography uses light interference, whereas normal photography uses wave optics.
The light from a laser is split into two parts by a mirror.
The reference beam shines on a piece of film.
Light from the object is interfering with the reference beam.
The exposed film looks foggy, but close examination shows a complicated interference pattern on it.
The film is darkened where the interference was constructive.
Holography uses the wave characteristics of light as compared to normal photography, which requires a lens.
A piece of film is interfered with by a single wavelength coherent light from a laser.
A partially silvered mirror splits the laser beam into two parts, one illuminating an object and the other shining directly on the film.
Light falling on a hologram can create a three-dimensional image.
The film's exposed regions are dark and block the light, while less exposed regions allow light to pass.
The film acts like a collection of gratings.
Light passing through the hologram is diffracted in various directions, producing both real and virtual images of the object used to expose the film.
The interference pattern is the same as the object.
The interference pattern gives you different perspectives when you move your eye to different places.