Higher Harmonics of High Power Lasers on the Basis of Yb- and Nd-doped Materials (213 nm, 266 nm)

The harmonics of Nd:YAG and Nd:YVO₄ lasers are widely used for material processing as well as for measurement applications. LAYERTEC offers a variety of optics for the fourth (266 nm) and fifth (213 nm) harmonic. All designs are calculated according to customer specifications.

Multiple Wavelength Mirrors

Fig.1:Reflectance spectra of a dual wavelength turning mirror for 266 nm and 355 nm

Fig.2:Reflectance spectra of a four wavelength turning mirror:
HRs (45°, 266 nm + 355 nm) > 99 %
+ HRs (45°, 532 nm + 1064 nm) > 99.9 %

Separators for the Fourth Harmonic

Fig.3:Reflectance spectra of a separator reflecting the fourth harmonic and transmitting the lower harmonics and the fundamental wave

Separators for the Fifth Harmonic

Fig.4:Reflectance spectra of fluoride coatings on CaF₂:

a)Turning mirror for the fifth harmonic (measured spectra)

b)Separator reflecting the fifth harmonic and transmitting the lower harmonics and the fundamental

Special Separators

The fifth harmonic at 213 nm is a critical wavelength for oxide coatings because the absorption edge of aluminum oxide begins in this wavelength range. However, aluminum oxide is the only high index oxide material which can be used for 213 nm. Compared to fluorides, oxide coatings are hard and show low scattering losses. Fluorides in contrast exhibit higher LIDT values and extended lifetime for medium and high power applications.

Fig.5:Reflectance spectra of separators for the fourth and fifth harmonics:
HRu (45°, 266 nm) > 98 % + Ru (45°, 213 nm) < 10 % for unpolarized light

a)Oxide coating optimized for low scattering losses

b)Fluoride coating for high laser-induced damage thresholds

Thin Film Polarizers

Sputtering techniques enable LAYERTEC to offer thin film polarizers also for the fourth harmonic of the Nd:YAG laser.

Fig.6:Reflectance spectrum of a thin film polarizer for 266 nm:
HRs (56°, 266 nm) > 98 % + Rp (56°, 266 nm) < 5 %,
Tp (56°, 266 nm) ≈ 95 %

Table 1:Common specifications of separators for the harmonics in the UV

Separator Type	Technology	Reflectance at Center Wavelength		Reflectance at the Corresponding Longer Nd:YAG Wavelengths
				266 nm		355 nm		532 nm		1064 nm
		Rs	Rp	Rs	Rp	Rs	Rp	Rs	Rp	Rs	Rp
3^rd harmonic, 355 nm	IAD	> 99.9 %	> 99.5 %					< 5 %	< 2 %	< 10 %	< 2 %
3^rd harmonic, 355 nm	Sputtered	> 99.9 %	> 99.8 %					< 2 %	< 1 %	< 2 %	< 1 %
4^th harmonic, 266 nm	IAD	> 99.7 %	> 99.4 %			< 5 %	< 2 %	< 10 %	< 2 %	< 10 %	< 2 %
4^th harmonic, 266 nm	Sputtered	> 99.8 %	> 99.5 %			< 5 %	< 1 %	< 2 %	< 1 %	< 2 %	< 1 %
5^th harmonic, 213 nm*	Evaporated	> 97 %	> 93 %	< 5 %	< 2 %	< 10 %	< 2 %	< 10 %	< 2 %	< 10 %	< 2 %
* Fluoride coating on CaF₂