Laser Helpers

The General Conference on Weights and Measures (CGPM) was formed by diplomatic accord and subsequently formulated the Treaty of the Meter. Originally, 17 nations (the United States inclusive) signed the agreement in Paris on May 20, 1875 with 48 nations currently designated as members.

The International System of Units – SI (derived from: Systeme International d’Unites) is administered by the International Bureau of Weights and Measures and periodically convenes its General Conference on Weights and Measures to evaluate measurement requirements.

The SI were formally adopted by CGPM in 1960. They consist of seven base units which, by convention are without reference to any other unit(s), and therefore regarded as independent. There are 22 other derived units which are formed according to various combinations with the base units.

Seven SI Base Units
Base Quantity	Name	Symbol
length	meter	m
mass	kilogram	kg
time	second	s
electric current	ampere	A
thermodynamic temperature	kelvin	K
amount of substance	mole	mol
luminous intensity	candela	cd

Sampling of Laser Photonics Derived Quantities
Derived Quantity	Name	Symbol	Expressed in SI Base Units
plane angle	radian	rad	m·m-1 = 1
solid angle	steradian	sr	m2·m-2 = 1
frequency	hertz	Hz	s-1
energy, work, quantity of heat	joule	J	m2·kg·s-2
power, radiant flux	watt	W	m2·kg·s-3

SI Prefixes & Symbols Denoting Powers of 10
Prefix	Multiple	Symbol
yotta	1024	Y
zetta	1021	Z
exa	1018	E
peta	1015	P
tera	1012	T
giga	109	G
mega	106	M
kilo	103	k
hecto	102	h
deca	10	da
deci	10-1	d
centi	10-2	c
milli	10-3	m
micro	10-6	mu or µ
nano	10-9	n
pico	10-12	p
femto	10-15	f
atto	10-18	a
zepto	10-21	z
yocto	10-24	y