WorksheetsElectrical pumping — extraction
Total questions: 86
Worksheet time: 46mins
A gas laser is a type of laser in which what serves as the active medium or laser medium?
a mixture of gas
a semiconductor crystal
a dye solution
a metal vapor target
According to the text, which gas laser is most commonly used in college laboratories?
helium–neon laser
carbon dioxide laser
Nd:YAG solid‑state laser
dye laser
Which statement best describes the main advantage of gas lasers over solid‑state lasers as stated in the material?
They are less prone to damage by overheating so they can be run continuously.
They produce only ultraviolet radiation and therefore are safer.
They require no electrical power to operate.
They are always more compact than diode lasers.
Within gas lasers, which type is identified as very high‑power in the material?
carbon dioxide laser
helium–neon laser
argon‑ion laser
excimer laser
The helium–neon laser was the first continuous‑wave laser ever constructed. Who built it in 1961?
Ali Javan
Theodore Maiman
Charles Townes
Arthur Schawlow
In He–Ne lasers, which pumping method is used to achieve excitation of electrons in the gas active medium?
electrical pumping by passing an electric current through the gas
optical pumping with a flashlamp
chemical pumping using reactive gases
nuclear pumping with radioactive sources
The helium–neon laser operates at a wavelength in the red portion of the visible spectrum. What is the typical wavelength stated?
532 nm
632.8 nm
1064 nm
405 nm
According to the description, the active medium in a helium–neon laser is which gas?
neon
helium
argon
krypton
What kind of energy‑level system characterizes the helium–neon laser as stated?
4‑level laser
2‑level laser
3‑level laser
5‑level laser
From the listed important wavelengths, which corresponds to the well‑known red line of the He–Ne laser?
0.6328μm
1.152μm
3.3913μm
0.5435μm
Based on the energy‑level diagram of the He–Ne laser (figure 1), what process provides excitation of atoms?
electric discharge by accelerated electrons
optical pumping with external light
pure thermal heating of the gas
chemical reaction between gases
What is the stated role of helium gas in the He–Ne laser?
It increases excitation efficiency by transferring energy to neon but does not participate directly in the lasing transition.
It is the only lasing species and produces the output directly.
It cools the discharge tube without affecting excitation.
It blocks spontaneous emission to narrow the linewidth.
Which statement correctly summarizes the two‑stage excitation process of neon atoms in the He–Ne laser?
High voltage accelerates electrons that excite helium; excited helium atoms then collide with neon to transfer energy for excitation.
High voltage directly excites neon atoms; neon then transfers energy to helium to produce lasing.
An optical flash first excites neon; a second flash excites helium to emit radiation.
Helium atoms absorb the laser light and re‑emit it to pump neon.
Why is helium particularly valuable for increasing the efficiency of the He–Ne lasing process as stated in the material?
An excited state of helium (labeled E5) has an energy very similar to an excited state of neon (also labeled E5), enabling efficient energy transfer.
Helium has a much higher mass than neon, preventing collisions.
Helium directly produces the red emission line without neon.
Helium forms stable molecules that trap excitation for long periods.
By approximately what factor does the lasing efficiency increase when helium gas is used in the He–Ne laser, according to the text?
2
20
200
2000
Identify the three main structures of a helium–neon laser.
Plasma tube
Optical cavity
Power supply
Cooling system
What is the approximate diameter of the thin inner tube in a helium–neon laser?
2 mm
2.5 cm
10 mm
25 mm
What is the approximate diameter of the thick outer tube that surrounds the inner tube?
2 mm
2.5 cm
25 mm
5 cm
What purpose do the outer tubes serve in a helium–neon laser? Select all that apply.
Protect the inner tube and laser mirrors from movements
Act as a large gas reservoir that refreshes Neon absorbed by the cathode
Increase the beam divergence for easier alignment
Provide optical pumping by an external flashlamp
Where is the lasing process (which creates the electromagnetic radiation) confined in a helium–neon laser?
Inside the inner tube filled with the gas mixture
Inside the outer tube acting as a reservoir
Between the mirrors outside the tube
Inside the power supply housing
Approximately what fraction of the gas mixture in a helium–neon laser is Helium?
85–90%
10–15%
50%
95–100%
Approximately what fraction of the gas mixture in a helium–neon laser is Neon?
10–15%
85–90%
1–5%
30–40%
What is the typical gas pressure inside the helium–neon laser tube?
0.01 Atmosphere (≈10 torr)
1 Atmosphere (≈760 torr)
0.1 Atmosphere (≈76 torr)
10 Atmospheres
At the ends of the tube, the electrodes are attached to which supply?
A high voltage power supply (AC or DC)
A low voltage battery
A solar power module
A mechanical pump
In the schematic of the helium–neon laser, which mirror allows partial transmission to form the laser output?
Output coupler
High reflector
Anode
Cathode
What is the typical length scale of the thin inner tube in a helium–neon laser?
Tens of centimeters
A few millimeters
Several meters
A few micrometers
Lasing action in copper vapor was first demonstrated in which year?
1966
1972
1980
1995
Around when did the first commercial copper vapor lasers appear?
1966
1975
1980
1990
Which of the following is a primary emission wavelength of a copper vapor laser?
510.6 nm
488.0 nm
632.8 nm
1064 nm
Which feature is cited as making the copper vapor laser attractive?
Relative high efficiency in the visible spectrum and high pulse power
Continuous-wave operation in the deep ultraviolet
Inherently fiber-coupled output without optics
Room-temperature operation without heating
In a copper vapor laser, the primary wavelengths are 510 nm and 578 nm. In which region of the spectrum are these generated?
Green and yellow
Red and infrared
Ultraviolet and blue
Microwave
What is the typical pulse repetition rate during normal operation of a copper vapor laser?
A few hertz
Several tens of kilohertz
Several megahertz
Direct current (no pulses)
In metal vapor lasers such as CVL, what directly excites the metal atoms?
Optical pumping by an external lamp
A chemical reaction in the tube
A fast electric discharge
Thermal radiation from the mirrors
Approximately what temperature is the discharge tube heated to in order to produce copper vapor at about 0.1 mbar?
1500 °C
500 °C
100 °C
3000 °C
Which buffer gas is added in several millibars to prevent window contamination and loss of copper in a copper vapor laser?
Neon
Argon
Helium
Nitrogen
What transmission is typically chosen for the output window of a copper vapor laser tube, while the rear mirror is a total reflector?
90% transmission
10% transmission
50% transmission
0% transmission
What is a typical beam diameter range obtainable from copper vapor lasers?
10–50 mm
0.5–2 mm
100–200 mm
1–2 µm
For a stable output-window-type resonator in a copper vapor laser, what is the typical beam divergence?
3–5 mrad
0.1 mrad
20–30 mrad
1 rad
What is the melting temperature of copper relevant to copper vapor laser operation?
1083 °C
850 °C
1400 °C
2000 °C
Inside a copper vapor laser tube during operation, the copper vapor pressure is approximately what value?
0.1 Torr
1 Torr
10 Torr
760 Torr
What approximate temperature range can be measured on the outside of the copper vapor laser tube during operation?
1400–1500 °C
200–300 °C
700–800 °C
50–100 °C
Over time, what maintenance action is stated as necessary for a copper vapor laser tube?
Insert new copper after a few hundred hours of operation
Refill the neon buffer gas daily
Replace both mirrors every hour
Cool the tube below the melting point every minute
In a copper vapor laser, what process excites copper vapor molecules into high laser energy levels?
Collisions with accelerated electrons from high-voltage pulses
Resonant absorption of sunlight
Radio-frequency magnetic pumping
Chemical combustion
How many energy levels make up the working scheme of a copper vapor laser?
Two
Three
Four
Five
Which pair lists the two emission wavelengths indicated for a copper vapor laser?
510 nm and 578 nm
633 nm and 543 nm
1064 nm and 532 nm
355 nm and 266 nm
In the described helium–cadmium laser, the cadmium metal is heated to what temperature to create the appropriate vapor pressure?
150 °C
250 °C
350 °C
450 °C
According to the passage on the He–Cd laser, the helium gas in the tube is maintained at what pressure?
0.3–0.7 millitorr
3–7 millitorr
30–70 millitorr
300–700 millitorr
Why does the helium remain electrically neutral in the He–Cd laser as described?
It is a noble gas with a very high excitation energy of 24.46 eV.
Cadmium has the higher excitation energy, preventing helium ionization.
The helium pressure is too low for any collisions to occur.
Helium atoms are negatively charged and cannot be ionized.
Which species moves toward which electrode in the He–Cd laser described?
Positive cadmium atoms move toward the negative cathode.
Negative cadmium ions move toward the positive anode.
Neutral helium atoms drift toward the negative cathode.
Positive helium ions move toward the negative cathode.
In designing the tube of a helium–cadmium laser, most of the effort is directed toward minimizing what?
The amount of helium atoms in the cavity
The amount of cadmium ions on the cathode
The overall gas pressure in the tube
Temperature fluctuations above 500 °C
What material loss is reported for the best He–Cd lasers after 1000 hours of operation?
1 g of cadmium metal
10 g of cadmium metal
1 g of helium gas
Negligible loss (approximately 0 g)
How do the gain and power output of the main two lines of the He–Cd laser compare with other lasers mentioned?
Higher than for the He–Ne laser but less than for the Ar+ laser
Lower than both the He–Ne and Ar+ lasers
Higher than both the He–Ne and Ar+ lasers
Equal to the He–Ne laser but greater than the Ar+ laser
What pair of excitation energies is given for helium and cadmium in the passage?
Helium 24.46 eV and cadmium 8.96 eV
Helium 8.96 eV and cadmium 24.46 eV
Both helium and cadmium 24.46 eV
Both helium and cadmium 8.96 eV
In the CO2 laser operation described, what initiates the transfer of energy to the nitrogen and CO2 molecules in the laser tube?
An electric discharge that accelerates electrons
Thermal conduction from the cavity mirrors
Optical pumping with a flashlamp
Radioactive decay within the tube
What total gas pressure is specified for the CO2 laser tube in the description?
5–30 Torr
0.5–3 Torr
50–300 Torr
1 atm
According to the stated gas mixture, which of the following are included in the CO2 laser tube composition? Select all that apply.
About 10% CO2 gas
About 10% N2
The remainder is He
The mixture is entirely CO2
Helium molecules are added to the gas mixture in order to: Select all that apply.
Empty the lower laser energy level so that population inversion is maintained
Stabilize the electrical discharge by taking heat away from the lasing area
Raise the upper laser level energy to increase gain
Increase the nitrogen concentration for stronger excitation
According to the description, nitrogen molecules help the process by:
Facilitating excitation of CO2 molecules via similar vibrational energy levels
Absorbing laser light to prevent population inversion
Catalyzing formation of ozone to cool the tube
Removing heat from the lasing area by conduction
The first vibrational energy level of the nitrogen molecule is very similar to which mode of the CO2 molecule?
The asymmetric stretching mode
The symmetric stretching mode
The bending mode
A pure rotational mode
In the described mechanism, energy can be easily transferred:
From excited nitrogen molecules to CO2 molecules
From CO2 molecules to nitrogen molecules
From helium molecules to nitrogen molecules
Only directly from electrons to CO2 molecules
What is the active medium in nitrogen lasers as described in the passage?
Nitrogen gas
Argon gas
Helium–neon mixture
Carbon dioxide
According to the passage, what pressure range of nitrogen gas is used in nitrogen lasers?
1 to 5 Torr
10 to 20 Torr
25 to 75 Torr
100 to 300 Torr
The passage states that in some nitrogen lasers the gas flows in the tube, while others have which alternative configuration?
A pressurized chamber
A sealed tube
An open-cavity cell
A fiber-delivered reservoir
Like most gas lasers, the nitrogen laser operates based on transitions between which energy levels?
Rotational energy levels
Electronic energy levels only
Vibration energy levels
Nuclear energy levels
How is the nitrogen laser excited according to the passage?
Optically pumped
Chemically excited
Thermally excited
Electrically excited
Based on the energy level diagram of the nitrogen laser, what is the labeled wavelength of the laser transition?
632.8 nm
337.1 nm
488.0 nm
10.6 µm
Using the provided description and diagram, explain the basic laser action in a nitrogen laser, identifying the initial excitation, the type of energy levels involved, and the transition responsible for emission.
Transverse excitation: In a transverse arrangement for gas lasers, how are the directions of discharge excitation and laser emission oriented relative to each other?
Perpendicular
Parallel
At 45 degrees
Randomly oriented
Transverse excitation: The two parallel electrodes in the design are separated by what approximate distance?
Several centimeters
About a few millimeters
About a few micrometers
About a meter
Excimer laser molecular gas: From what kind of molecule is the radiation emitted in this type of laser?
A stable ground-state molecule
A molecule that exists only for a very short time
A triatomic molecule with a permanent dipole
A crystalline lattice defect
Excimer composition: An excimer molecule for these lasers is composed of what combination of atoms?
Two halogen atoms
Two noble gas atoms
A noble gas atom and a halogen atom
A hydrogen atom and a halogen atom
Excimer definition: Which statement describes the existence of an excimer in ground and excited states?
It is bound in both ground and excited states
It is unbound in the excited state and bound in the ground state
It has a bound state only in the excited state and does not exist as a bound molecule in the ground state
It is permanently dissociated in all states
Name origin: The term Excimer comes from the phrase that means a molecule composed of two atoms existing only in an excited state. What is that phrase?
Excited trimer
Excited dimer
Excited monomer
Excited polymer
History: The first demonstration of excimer-laser stimulated emission at 172 nm from Xe2 gas, pumped by a beam of electrons, occurred in which year and country?
1971 in the USSR
1975 in the USA
1960 in the UK
1980 in Japan
History: The first laser action in a noble gas with halogen (XeBr) was reported by which researchers and in what year?
Basov and Popov in 1971
Searl and Hart in 1975
Townes and Schawlow in 1960
Basov and Danilychev in 1980
Identify from the table: Which excimer laser is associated with a characteristic wavelength near 193 nm?
ArF
KrF
XeCl
ArCl
Identify from the table: Which pair of wavelengths belongs to KrF excimer lasers?
175 nm and 193 nm
248 nm and 275 nm
308 nm and 351 nm
351 nm and 460 nm
Energy levels: Why is population inversion readily achieved in excimer lasers according to the description?
Because the ground state is lower in energy than the excited state
Because the lower laser level has zero population while a bound state exists only in the excited state
Because continuous-wave pumping keeps both levels equally populated
Because the ground state has a deep potential well
Notation: In the energy-level discussion, what do the letters R and H represent in the excimer molecule?
R is halogen and H is noble gas
R is noble gas and H is halogen
R is hydrogen and H is helium
R is reaction coordinate and H is enthalpy
Energy diagram: Which state of the excimer molecule shows a potential well indicating a momentary stable bound state?
Ground state
Excited state
Both ground and excited states
Neither state
Energy diagram: According to the figure, in which spectral region do laser transitions of the excimer occur?
Infrared
Visible
Ultra-violet
X-ray
According to the excerpt titled Operation of the Excimer Laser, what fraction of halogen is present in the gas mixture inside the excimer laser tube?
Very little halogen (0.1–0.2%)
About 1–2% halogen
About 10–20% halogen
About 50% halogen
Based on the excerpt titled Operation of the Excimer Laser, which noble gases are listed as the small added noble gas component in the mixture? Select all that apply.
Argon
Krypton
Xenon
Neon
From the excerpt titled Operation of the Excimer Laser, which component makes up about 90% of the gas mixture inside the tube?
Neon or Helium
Argon
Chlorine
Hydrogen
According to the excerpt titled Operation of the Excimer Laser, which of the following are cited sources of halogen atoms used in the gas mixture? Select all that apply.
F2
Cl2
Br2
HCl
CO2
According to the excerpt titled Operation of the Excimer Laser, what is the stated advantage of using a compound instead of a pure halogen in the gas mixture?
It avoids the strong chemical activity of the halogen molecule (especially Fluorine)
It increases the operating pressure of the laser tube
It reduces the optical alignment requirements
It shifts the laser to a longer wavelength
