Bauteile für höhere Harmonische der Nd:YAG und Nd:YVO4 Laser

The harmonics of Nd:YAG and Nd:YVO4 lasers are widely used for materials processing as well as for measurement applications. On these pages we introduce dual wavelength mirrors and separators for the fourth (266nm) and fifth harmonic (213nm). All designs are calculated according to customer specification.

dual wavelength turning mirror for 266nm and 355nmFigure 1: ReflectaReflectance spectra of a dual wavelength turning mirror for 266nm and 355nm (a) and a separator for the fourth harmonic from the long wavelength harmonics and the ground wavelength (b)
turning mirrorFigure 2: Measured reflectance spectra of a turning mirror for the fifth harmonic (a) and of a separator for the fifth harmonic from the long wavelength harmonics and the ground wavelength (b); fluoridic coatings on CaF2
Separator
type
Centre
wavelength
Reflectance at centre
wavelength [%]
Reflectance at the corresponding longer
Nd:YAG wavelengths [%]
266nm355nm532nm1064nm
RsRpRsRpRsRpRsRpRsRp
3rd harmonic355nm> 99.7> 99< 5< 2< 10< 2
4th harmonic266nm> 99.7> 99< 5< 2< 10< 2< 10< 2
5th harmonic213nm> 97> 93< 5< 2< 10< 2< 10< 2< 10< 2
Table 1:Common specifications of separators for the harmonics in the UV
* Fluoridic coating on CaF2

separators for the second harmonic from the fourth harmonicFigure 3: Reflectance spectra of separators for the second harmonic from the fourth harmonic:
(a): HR (0°, 532nm) > 99.5% + R (0°, 266nm) < 10% (rear side uncoated)
(b): HR (0°, 532nm) > 99.9% + R (0°, 266nm) < 5% (rear side uncoated)

Components for 266nm are normally produced by e-beam evaporation. These coatings exhibit high damage thresholds, but the reflectivity in the visible spectral range is limited to R > 99.5% (see figure 3a). Recent research results on sputtered coatings for the UV show, that separators with a significantly improved reflectivity in the VIS can be produced, which have similar properties in the UV (see figure 3b).
separators for the fourth and fifth harmonicsFigure 4: Reflectance spectra of separators for the fourth and fifth harmonics:
HRr (45°, 266nm) > 98% + Rr (45°, 213nm) < 10% for unpolarized light
a) oxide coatings optimized for low straylight losses (rear side uncoated)
b) fluoride coatings for high laser induced damage thresholds (rear side uncoated)

The fifth harmonic at 213nm is a critical wavelength for oxide coatings, because the absorption edge of aluminum oxide begins in this wavelength range. For high power applications we recommend fluoridic coatings on calcium fluoride which are produced according to the technology of ArF-excimer laser mirrors.

Thin Film Polarizers

thin film polarizers for 266 nm and 213 nmFigure 5: RReflectance spectra of thin film polarizers for 266nm (a) and 213nm (b):
a) HRs(56°, 266 nm) > 98 % + Rp(56°, 266 nm) < 1 %
b) HRs(56°, 213 nm) > 97 % + Rp(56°, 213 nm) < 5 %;
Please note that Tp ist only about 75% because of the above mentioned absortion losses

Magnetron sputtering enables us to offer thin film polarizers also for the fourth and fifth harmonic of the Nd:YAG laser.