Reflectivity of Molybdenum laser mirrors

Because molybdenum metal is exceptionally hard and durable, “Moly” mirrors are widely used with high power CO2 lasers for welding and metal cutting. Other uses are in industrial monitoring, chemical sensing, spectroscopy etc. We often get asked about the optical properties of Molybdenum. Experimental data is scarce, especially at non standard angles of incidence, and often doesn’t take account of polarisation anisotropy. It is possible to model the optical properties of polished metals, based on the complex refractive index of the metal, and we find there is a very good agreement between the theoretical values, and the few data points we can measure in our test lab (using a CO2 laser, and a circular polarised beam).   Below are the calculated reflectivity values of polished molybdenum a few selected wavelengths for 45 degrees incidence. As you can see below 2 microns wavelength, uncoated bare Mo surfaces aren’t greatly reflective.

Wavelength

%R S pol

%R P pol

Phase Shift deg

633nm HeNe

67

43

11

850nm

66

45

11

1064nm Nd:YAG laser

77

60

6

2.94um Er:YAG laser

98.4

96.8

5

4um

98.7

97.6

5

9um

98.9

97.9

1.6

10.6 CO2 laser

98.9

98

1.3

12um

98.9

97.9

1

Theoretical Optical Reflectivity of Molybdenum at 45 Degree incidence

We have the ability to calculate reflectivity and phase shift for a range of metals used as reflectors at varying incidences and wavelengths, for example Aluminium.  Do see our web page on Molybdenum mirrors

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