Section: 10 | Characteristics of Laser Sources |
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John R. Rumble, ed., CRC Handbook of Chemistry and Physics, 102nd Edition (Internet Version 2021), CRC Press/Taylor & Francis, Boca Raton, FL.
If a specific table is cited, use the format: "Physical Constants of Organic Compounds," in CRC Handbook of Chemistry and Physics, 102nd Edition (Internet Version 2021), John R. Rumble, ed., CRC Press/Taylor & Francis, Boca Raton, FL.

CHARACTERISTICS OF LASER SOURCES

William F. Krupke

Light amplification by stimulated emission of radiation was first demonstrated by Maiman in 1960, the result of a population inversion produced between energy levels of chromium ions in a ruby crystal when irradiated with a xenon flashlamp. Since then population inversions and coherent emission have been generated in literally thousands of substances (neutral and ionized gases, liquids, and solids) using a variety of incoherent excitation techniques (optical pumping, electrical discharges, gas-dynamic flow, electron-beams, chemical reactions, nuclear decay).

The extrema of laser output parameters that have been demonstrated to date and the laser media used are summarized in Table 1. Note that the extreme power and energy parameters listed in this table were attained with laser systems rather than with simple laser oscillators.

Laser sources are commonly classified in terms of the state-of- matter of the active medium: gas, liquid, and solid. Each of these classes is further subdivided into one or more types as shown in Table 2. A well-known representative example of each type of laser is also given in Table 2 together with its nominal operation wavelength and the methods by which it is pumped.

The various lasers together cover a wide spectral range from the far ultraviolet to the far infrared. The particular wavelength of emission (usually a narrow line) is presented for some six dozen lasers in Figures 1A and 1B.

By suitably designing the excitation source and/or by controlling the laser resonator structure, laser systems can provide continuous or pulsed radiation as shown in Table 3.

Besides the method of excitation and the temporal behavior of a laser, there are many other parameters that characterize its operation and efficiency, as shown in Tables 4 and 5.

Although many lasers only emit in one or more narrow spectral “lines,” an increasing number of lasers can be tuned by changing the composition or the pressure of the medium, or by varying the wavelength of the pump bands. The spectral regions in which these tunable lasers operate are presented in Figure 2.

Reference

TABLE 1. Extrema of Output Parameters of Laser Devices or Systems



ParameterValueLaser medium
Peak power1 × 1014 W (collimated)Nd:glass
Peak power density1018 W/cm2 (focused)Nd:glass
Pulse energy>105 JCO2, Nd:glass
Average power105 WCO2
Pulse duration3 × 10-15 s continuous wave (cw)Rh6G dye; various gases, liquids, solids
Wavelength60 nm ↔ 385 µmMany required
Efficiency (nonlaser pumped)70%CO
Beam qualityDiffraction limitedVarious gases, liquids, solids
Spectral linewidth20 Hz (for 10-1 s)Neon-helium
Spatial coherence10 mRuby


TABLE 2. Classes, Types, and Representative Examples of Laser Sources



Type (characteristic)Representative exampleNominal operating wavelength (nm)Method(s) of excitation
Gas
Atom, neutral (electronic transition)Neon-Helium (Ne-He)633Glow discharge
Atom, ionic (electronic transition)Argon (Ar+)488Arc discharge
Molecule, neutral (electronic transition)Krypton fluoride (KrF)248Glow discharge; e-beam
Molecule, neutral (vibrational transition)Carbon dioxide (CO2)10600Glow discharge; gasdynamic flow
Molecule, neutral (rotational transition)Methyl fluoride (CH3F)496000Laser pumping
Molecule, ionic (electronic transition)Nitrogen ion (N2+)420E-beam
Liquid
Organic solvent (dye-chromophore)Rhodamine dye (Rh6G)580–610Flashlamp; laser pumping
Organic solvent (rare earth chelate)Europium:TTF612Flashlamp
Inorganic solvent (trivalent rare earth ion)Neodymium:POCl41060Flashlamp
Solid
Insulator, crystal (impurity)Neodymium:YAG1064Flashlamp, arc lamp
Insulator, crystal (stoichiometric)Neodymium:UP(NdP5O14)1052Flashlamp
Insulator, crystal (color center)F2:LiF1120Laser pumping
Insulator, amorphous (impurity)Neodymium:glass1061Flashlamp
Semiconductor (p-n junction)GaAs820Injection current
Semiconductor (electron-hole plasma)GaAs890E- beam, laser pumping


figure 1a

FIGURE 1A. Wavelengths of lasers operating in the 120 to 1200 nm spectral region.

figure 1b

FIGURE 1B. Wavelength of lasers operating in the 1300 to 12,000 nm spectral region.

TABLE 3. Temporal Characteristics of Lasers and Laser Systems



FormTechniquePulse width range(s)
Continuous waveExcitation is continuous; resonator Q is held constant at some moderate value
PulsedExcitation is pulsed; resonator Q is held constant at some moderate value10-8 – 10-3
Q-SwitchedExcitation is continuous or pulsed; resonator Q is switched from a very low value to a moderate value10-8 – 10-6
Cavity dumpedExcitation is continuous or pulsed; resonator Q is switched from a very high value to a low value10-7 – 10-5
Mode lockedExcitation is continuous or pulsed; phase or loss of the resonator modes is modulated at a rate related to the resonator transit time10-12 – 10-9


TABLE 4. Properties and Performance of Some Continuous Wave (CW) Lasers



ParameterUnitNe-He (gas)Ar+ (gas)CO2 (gas)Rhodamine 6G dye (liquid)Nd:YAG (solid)GaAs (solid)
Continued on next page...
Excitation methodDC dischargeDC dischargeDC dischargeAr+ laser pumpKrypton arc lampDC injection
Gain medium compositionNeon:heliumArgonCO2:N2:HeRh 6G:H2ONd:YAGp:n:GaAs
Gain medium densityTorr0.1:1.00.40.4:0.8:5.0
ions/cm32(18):2(22)1.5(20):2(22)2(19):3(18):3(22)
Wavelengthnm633488106005901064810
Laser cross-sectioncm-23(-13)1.6(-12)1.5(-16)1.8(-16)7(-19)~6(-15)
Radiative lifetime (upper level)s~1(-7)7.5(-9)4(-3)6.5(-9)2.6(-4)~1(-9)
Decay lifetime (upper level)s~1(-7)~5.0(-9)~4(-3)6.0(-9)2.3(-4)~1(-9)
Gain bandwidthnm2(-3)5(-3)1.6(-2)800.510
Type, gain saturationInhomogeneousInhomogeneousHomogeneousHomogeneousHomogeneousHomogeneous
Homogeneous saturation fluxW cm-2~203(5)2.3(3)~2(4)
Decay lifetime (lower level)s~1(-8)~4(-10)~5(-6)<1(-12)<1(-7)<1(-12)
Inversion densitycm-3~1(9)2(10)2(15)2(16)6(16)1(16)
Small signal gain coefficientcm-1~1(-3)~3(-2)1(-2)45(-2)40
Pump power densityW cm-339000.151(6)1507(7)
Output power densityW cm-32.6(-3)~12(-2)3(5)955(6)
Laser size (diameter:length)cm:cm0.5:1000.3:1005.0:6001(-3):0.30.6:105(-4):7(-3);2(-2)a
Excitation current/voltageA/V3(-2):2(3)30:3000.1:1.5(4)90:1251.0/1.7
Excitation current densityA cm-20.156006(-3)1404.5(3)
  • a Junction thickness:width:length.
  • b Pressure dependent.


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