Absorption wavelength spectrum for different materials: glass, metal and others.

There is a problem that some lasers do not cut or engrave on different materials, for example, metals, glass, plexiglass.

An explanation is very simple – different materials absorb and reflect different wavelengths, therefore, more power is absorbed – easy cutting or engraving will be. More power is being reflected – less power will achieve the surface.

about absorption reflection transmission principles

Reflectance for Aluminum Silver Gold and Copper

Under this plot you may see that Al, Ag, Au, Cu reflect almost all wavelengths after 1000 nm.

Absorption for Silver, Aluminum, Gold, Copper, Steel, Iron vs wavelength (different types of lasers)

(c) www.researchgate.net
Based on Researchgate data you may see that aluminum absorbs wavelength shorter than 100 nm and almost does not of other wavelengths, has a small spike somewhere 850-900 nm.
For example, gold and silver are kind of sensitive to the wavelength 300-500 nm.
As you may see steel and pure iron are sensitive to wavelengths more than 1050 nm. which is why most fiber lasers for metal cutting use 1064 / 1080 nm wavelength.

This Data is For a Copper Standard Solution And Bears No Resemblance To Elemental Copper Metal
This Plot Shows Substantial Copper Absorption (About 43 %) at 450 nm

Absorption coefficient depending on wavelength for Copper Gold, Nickel, Iron and Aluminum

(c) www.keyence.com
According to Keyence’s research, you may see that all metals except aluminum have downslope after 450 nm.

Why it is impossible to engrave or cut with lasers of wavelength more than 300 nm

(c) www.chem.ucla.edu
As you can see on this chart almost all types of glass are transmitting all wavelength longer than 300 nm

Glass cutting is possible with the laser with a wavelength of more than 4.4uM (4400 nm)

(c) www.crystran.co.uk
The regular glass absorbs wavelength longer than 4000 nm (4 uM) which is far-infrared, that is why laser cutting of glass and acrylic can be don on Co2 lasers with a wavelength of 10.6 uM.

Acrylic transition coefficient

Window glass transition coefficient

Different types of glass transmission rate

Reflection rate in percentage (%) from a polished surface.

Types of wavelength	The wavelength, А (10A=1 nm)	Aluminum	Copper	Steel (1% С)	Silver	Nikel	Chrome	Zink	Silicium
Ultraviolet	1880	–	–	22	76	–	33	17	64
	2000	–	–	27	76	–	36	22	73
	2510	80	26	38	34	38	–	39	75
	3050	–	25	44	9	44	37	48	73
	3570	84	27	50	75	49	41	51	60
Visible light	5000	88	44	56	91	61	55	55	34
	6000	89	72	57	93	65	–	58	32
	7000	87	83	58	95	69	56	61	–
Infrared	8000	85	89	61	97	70	–	62	–
	10000	93	90	63	97	72	57	69	–
	50000	94	98	90	99	94	81	97	–
	100000	97	98	94	99	–	93	–	–