 |
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
|
|
