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Chapter: 2 General physics
    Section: 2.5 Radiation and optics
        SubSection: 2.5.6 Laser radiation

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2.5.6 Laser radiation

The table which follows lists a selection of laser emissions from the many thousand that have been discovered: see, for example, M. J. Weber (ed.) (1982) Handbook of Laser Science and Technology, 2 vols, and (1991) Supplement: 1 Lasers, (CRC Press, Boca Raton, Florida, USA). The selection is restricted to those that are commercially available or are important for other reasons, such as their place in the spectrum or their high power. Whilst most lasers, especially powerful ones, are of fixed frequency, tunable coverage of much of the tabulated spectrum is available through the use of nonlinear devices to add or subtract laser frequencies, or to generate their harmonics. The table gives the vacuum wavelength, the method of excitation, the tunability, and an added note to cover power, pulse characteristics and other matters of interest. The vacuum wavelength λvac is related to the frequency f by λvac (μm) = 299 792 458/f(MHz), from the 1983 definition of the metre (see section 1.1.1).

Gaps in the spectral coverage may be related to strong absorption by atmospheric gases such as CO2 (at 1.4, 1.9 and 2.6–2.9 µm), or H2O (at 5.5–7.2 µm and in the far infrared). In parts of the infrared, the air wavelength varies strongly with atmospheric properties such as humidity.

Hazard classes (EN 60825, 1991, ANSI Z-136.1 (1986), IEC 825: 1984 + Amendment No. 1: 1990) have been established for laser systems based on internationally-agreed limits for exposure of the body to laser radiations (WHO Environmental Health Criteria No. 23, 1982). Of these, Class 1 are safe in normal use, and Class 2 emit visible radiation of < 1 mW for which eye-aversion reflexes provide protection. The higher classes 3a, 3b and 4 require special care. In the USA the classes are named respectively I, II, IIIa, IIIb and IV. Wavelengths 0.4–1.4 µm approximately can be focused by the eye on the retina and are therefore particularly dangerous. Blue to ultraviolet wavelengths also require care because of the high photon energy. Electric shock risks exist with most lasers, especially gas lasers, because high voltages and high electrical powers can be involved.

The cost of lasers varies from about £20 to more than £100,000. The cheapest lasers are semiconductor-diode lasers for room-temperature use and small dc-excited discharge devices such as the He–Ne gas laser. Such features as cryogenic operation and optical pumping, especially by lasers, add considerably to the cost, as do features such as mode-locking, single-mode output, line-tunability and frequency stabilization.


 λvac/μm

Name

Type/excitation

Tuning

Notes

 

 

 

 

 

0.157

  F2

    gas, dc

  ML

  p 10 mJ/10 ns, 3 lines (uv lasers are

 

 

 

 

      important as pump sources).

0.193 4

  ArF

    excimer, TEA

  ML

  p 1 mJ–0.5 J/5–20 ns, e 1%

0.249

  KrF

    excimer, TEA

  ML 50 ppm

  p 1 mJ–7 J/4–20 ns, e 2%, 2 lines

0.3–1.2

  dye

    liquid, o–p

  T 10%

  cw 0.01–1 W, p 10 W–10 MW/10 fs–1 μs,

 

 

 

 

       e 0.3–1%, versatile

0.325 1

  He–Cd

    metal vapour, dc

  few ppm

  cw 1–20 mW

0.337

  N2

    gas, dc

  62 lines, 0.2%

  p 10 μJ–30 mJ/1–10 ns, dye pump

0.351 212

  Ar ion

    gas, dc

  ML few ppm

  cw 0.025–0.8 W

0.413 250

  Kr ion

    gas, dc

  ML few ppm

  cw 0.05–1.8 W,

violet

0.441 69

  He–Cd

    metal vapour, dc

  few ppm

  cw 3–400 mW,

violet

0.458 06

  Ar ion

    gas, dc

  ML few ppm

  cw 0.1–1 W,

blue

0.488 122

  Ar ion

    gas, dc

  ML few ppm

  cw 5 mW–6 W, 2–8 μJ/<10–15 ns,

 

 

 

 

 

     m–l,

blue

0.510 696

  Cu

    metal vapour, dc

  few ppm

  p 0.2–10 mJ/20–50 ns, e 1%,

 

 

 

 

 

     1–40 W mean,

green

0.514 673

  Ar ion

    gas, dc

  ML few ppm

  cw 0.3–8 W, p < 8 μJ/ < 15 ns,

 

 

 

 

 

     FS (I2), m–l,

green

0.531 014

  Kr ion

    gas, dc

  ML few ppm

  cw 0.2–1.5 W, FS (I2)

green

0.532 275

  Nd/YAG × 2

    f-doubled YAG

  as 1.064 μm

  cw 0.1 W, p 100 mJ/7–20 ns, FS (I2)

green

0.543 516

  He–Ne

    gas, dc

  few ppm

  cw 0.1–1 mW,

green

0.568 348

  Kr ion

    gas, dc

  ML few ppm

  cw 0.1–1 W, FS (I2),

yellow

0.578 373

  Cu

    metal vapour, dc

  few ppm

  p 0.1–5 mJ/20–50 ns, e 0.3%,

 

 

 

 

 

     1–20 W mean,

yellow

0.611 971

  He–Ne

    gas, dc

  few ppm

  cw 0.01–2 mW, FS (I2),

orange

0.632 991

  He–Ne

    gas, dc

  few ppm

  cw 0.1–60 mW, FS (I2), most

 

 

 

 

 

     common laser,

red

0.640 283

  He–Ne

    gas, dc

  few ppm

  cw 0.01–0.1 mW, Fs (I2),

red

0.647 27

  Kr ion

    gas, dc

  ML few ppm

  cw 0.5–3.5 W,

red

0.66–0.68

  InGaAlP

    diode, dc (lv)

  T ~ 1%

  cw 0.3–10 mW, p 0.7 μJ/60 ps,

red

0.67–1.1

  Ti: sapphire

    s/s, o–p

  T ~ 15%

  cw < 3 W, p < 2.5 J/80 fs–6 μs,

 

 

 

 

 

     e < 35%,

red–IR

0.694 5

  Cr/ruby

    s/s, o–p (lamp)

  0.1% cooled

  p 1 mJ–30 J/15 ns–1 ms, the first

 

 

 

 

 

     laser,

red

0.72–0.80

  alexandrite

    s/s, o–p

  T 8%

   cw 0.6 W, e < 40%,

 

 

 

 

 

     p 0.1–0.7 J/100 ns,

red–IR

0.75–0.90

  GaAlAs

    diode, dc (lv)

  1% ext cav

  cw, 0.1–500 mW, 10 W, p < 10 W

 

 

 

 

 

     /10 ns–1 ms, e 10% +,

red–IR

0.752 75

  Kr ion

    gas, dc

  ML few ppm

  cw 0.1–1.2 W

red

0.82–3.3

  F-centre

    s/s, o–p

  T 20%

  cw 0.1–100 mW, temp 77–300 K

 

0.89–0.90

  GaAs

    diode, dc (lv)

  1% cooled

  cw 0.1–50 mW, 20 W, p < 50 W/1 ns–1 μs,

 

 

 

 

 

     first diode laser

 

1.064

  Nd/YAG

    s/s, o–p (lamp)

  0.03%

  cw < 50 W, p 10 mJ–50 J/3–200 ns &

 

 

 

 

 

     > 100 μs, e 1%, m–l

 

1.064

  Nd/YAG

    s/s, o–p (diode)

  0.03%

  cw < 0.3 W, e 10%, low noise

 

1.092 64

  Ar ion

    gas, dc

  ML few ppm

  cw 50–200 mW

 

1.1–1.6

  InGaAsP

    diode, dc (lv)

  0.5%, temp

  cw 0.1– 7 mW, p 50 mW/0.1–50 ns,

 

 

 

 

 

     optical fibre use

 

1.152 590

  He–Ne

    gas, dc

  few ppm

  cw 0.1–50 mW, first gas laser, FS (I2)

 

 

 

 

 

     at 2f

 

1.315 244

  I

    gas, o–p (lamp),

  6 lines/0.01%

  p 1–10 J/10 ns–6 μs, m–l, e 0.5%,

 

 

 

       chem

 

     0.1 s lifetime, cw (chem) < 4 W

 

1.319

  Nd/YAG

    s/s, o–p (lamp),

  as 1.064 μm

  cw 0.1–6 W, p, m–l

 

1.523 488

  He–Ne

    gas, dc

  few ppm

  cw 0.1–20 mW, FS (Ne)

 

1.53–1.57

  Er/glass

    fibre, o–p

  T 3%

  cw < 30 mW, amplifier to 200 mW

 

1.73

  Er/YLF

    s/s, o–p (lamp)

  as ruby

  p 5 mJ/0.2 μs

 

2.026 777

  Xe

    gas, dc

  few ppm

  cw 1–10 mW, long laser, non-commercial

 

2.06

  Ho/YLF

    s/s, o–p (lamp)

  —

  cw 5 W multimode

 

2.395 795

  He–Ne

    gas, dc

  few ppm

  cw 0.1–10 mW, non-commercial

 

 

 

 

      gas mixtture, 3 lines

2.6–3, 3.6–4.1

  HF, DF

    gas, chem., TEA

  ST few ppm

  cw 2–25 W, p 0.3–1 J/0.1–1 μs Lamp dip

3–30

  lead salt

    diode, dc (1v)

  T 10%, temp

  cw 0.1–0.5 mW, temp 15–90 K, various

 

 

 

 

      materials

3.392 231

  He–Ne

    gas, dc/rf

  few ppm

  cw 0.1–50 mW, accurate FS (CH4)

3.507 986

  Xe

    gas, dc

  few ppm

  cw 1–50 mW, FS (H2CO)

5–6.4

  CO

    gas, dc/chem

  ST few ppm

  cw 2–30 W p 3–10 mJ/1–1000 μs,

 

 

 

 

      e < 10%, atm. absorption, FS (CO)

9.0–11.0

  CO2

    gas, dc

  ST few ppm

  cw 1–50 W, 15 kW, FS (CO2),

 

 

 

 

       e ~ 5% ~ 1000 lines

9.0–11.0

  CO2 wg

    gas, dc/rf

  ST 10 ppm

  cw 0.1–250 W, FS (CO2, OsO4),

 

 

 

 

      compact, e >10%

9.0–11.0

  CO2 atm

    gas, TEA/o–p, rf

  T 1%

  p 10 mJ–3 J/100 ns + 3 μs tail, pressure

 

 

 

 

      1–10 atm

10.3–11.0

  N2O

    gas, dc

  ST few ppm

  cw 0.1–10 W, p

10.7–13.3

  NH3

    gas, o–p

  MLcw 1 ppm

  cw 0.2–10 W, e < 28%,

 

 

 

 

       p 10 mJ–1.4 J/200 ns, Raman process

15.3–16.4

  CF4

    gas, o–p

  ST few ppm

  cw 2 mW at 150 K, p 0.1 J/3 μs, e 1%

27.970 75

  H2O

    gas, dc

  ML few ppm

  cw 1–100 mW, FS (Lamb dip), & 78,

 

 

 

 

       119 μm lines

 

 

 

 

 

There are about 4000

  cw 0.1–10 mW

o–p lines between

  cw 1–50 mW

~20 μm and 2 mm but

  cw 1–50 mW

few give > 10 mW.

  cw 1–200 mW

Pumping is by

 

9–11 μm lines.

42.159 1

  CH3OH

    gas, o–p

  ML few ppm

70.511 6

  CH3OH

    gas, o–p

  ML few ppm

81.496 9

  NH3

    gas, o–p

  ML few ppm

118.834 1

  CH3OH

    gas, o–p

  ML few ppm

       

194.702 7

  DCN

    gas, dc

  ML few ppm

  cw 1–200 mW, 2 lines, & at 190 μm

214.579 1

  CH2F2

    gas, o–p

  ML few ppm

  cw 1–200 mW, & 184 μm strong line

336.557 8

  HCN

    gas, dc/rf

  few ppm

  cw 1–200 mW, early sub-mm laser, &

 

 

 

 

       311 μm line

385

  D2O

    gas, o–p

  0.1%

  p 10–140 mJ/0.2–1 μs, Raman process

570.568 7   CH3OH     gas, o–p   ML few ppm   cw 0.1–5 mW
 Microwave devices
 reach to wavelengths
 < 500 μm

963.487 3

  C2H3Br

    gas, o–p

  ML few ppm

  cw 0.2–5 mW

 

 

 

 

 

     For approximate air wavelengths in the visible subtract 2.8 parts in 104.
     Typical approximate values are given.


Symbols and abbreviations:

atm: atmosphere (pressure), atmospheric (absorption)
chem: chemical (the laser is pumped by a reaction when gases mix)
cw: continuous-wave
diode: semiconductor-junction diode (carrier injection laser)
e: efficiency (output power/excitation input power)
ext cav: in an external cavity resonator
FS(A): frequency standard when locked to a transition in system A, e.g. in I2
lv: low voltage, a few volts
λvac: vacuum wavelength
m–l: can be mode locked (to produce a train of sub-ns pulses)
ML: multiline (the laser can be tuned to different lines)
o–p: optically-pumped
p: pulsed
ppm: parts per million
s/s: solid state (lasing impurity in a uniform host crystal)
ST: step tunable (the laser can be tuned over a regularly-spaced set of lines)
T: continuously tunable (by a frequency-selective element in the cavity)
TEA: transversely-excited atmospheric
temp: temperature
wg: waveguide
YAG: yttrium aluminium garnet
YLF: yttrium lithium fluoride

D.J.E.Knight

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