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Optical Coatings

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V-<strong>Coatings</strong><br />

V-coatings are multilayer antireflection coatings that reduce the<br />

reflectance of a component to near-zero for one very specific wavelength.<br />

Our V-coatings are intended for use at normal incidence, for<br />

maximum reflectances of not more than 0.25% at their design wavelength.<br />

They are extremely sensitive to both wavelength and angle of<br />

incidence. For example, a V-coating intended for the helium neon<br />

wavelength (632.8 nm) when used at 30-degree incidence will reflect<br />

about 0.8%. At 45-degree incidence, the same coating will reflect over<br />

2.5%. If your application involves other than normal angles of<br />

incidence or high-numerical-aperture (low f-number) optics, it may<br />

be better to use a HEBBAR coating.<br />

Experience shows that the maximum reflectance typically<br />

achieved by these coatings is often closer to 0.1% than the 0.25%<br />

we specify. Using V-coatings on fused-silica optics can therefore<br />

provide exceptionally high external transmittances.<br />

V-Coating, Normal Incidence<br />

Wavelength<br />

(nm)<br />

193<br />

248<br />

266<br />

308<br />

351<br />

364<br />

442<br />

458<br />

466<br />

473<br />

476<br />

488<br />

496<br />

502<br />

514<br />

532<br />

543<br />

633<br />

670<br />

694<br />

780<br />

830<br />

850<br />

904<br />

1064<br />

1300<br />

1523<br />

1550<br />

Laser Type<br />

ArF<br />

ArF<br />

YAG 3rd harm.<br />

XeCl<br />

Ar ion<br />

Ar ion<br />

HeCd<br />

Ar ion<br />

Ar ion<br />

Ar ion<br />

Ar ion<br />

Ar ion<br />

Ar ion<br />

Ar ion<br />

Ar ion<br />

YAG 2nd harm.<br />

HeNe<br />

HeNe<br />

GaAlAs<br />

Ruby<br />

GaAlAs<br />

GaAlAs<br />

GaAlAs<br />

GaAs<br />

Nd:YAG<br />

InGaAsP<br />

HeNe<br />

InGaAsP<br />

Maximum<br />

Reflectance<br />

(%)<br />

0.5<br />

0.25<br />

0.25<br />

0.25<br />

0.25<br />

0.25<br />

0.25<br />

0.25<br />

0.25<br />

0.25<br />

0.25<br />

0.25<br />

0.25<br />

0.25<br />

0.25<br />

0.25<br />

0.25<br />

0.25<br />

0.25<br />

0.25<br />

0.25<br />

0.25<br />

0.25<br />

0.25<br />

0.25<br />

0.25<br />

0.25<br />

0.25<br />

COATING<br />

SUFFIX<br />

/101<br />

/102<br />

/103<br />

/104<br />

/105<br />

/107<br />

/111<br />

/112<br />

/113<br />

/114<br />

/115<br />

/116<br />

/117<br />

/118<br />

/119<br />

/122<br />

/121<br />

/123<br />

/128<br />

/124<br />

/163<br />

/166<br />

/167<br />

/125<br />

/126<br />

/168<br />

/169<br />

/169<br />

The typical reflectance curve illustrated in figure 5.30 is for a<br />

V-coating on BK7 optical glass. Clearly the performance of such a<br />

coating is highly dependent on the refractive index of the component<br />

material. However, we specify all coatings by performance<br />

figures and not by design. This means that we will change the design<br />

to suit the material being coated. This makes ordering coatings<br />

simple: select the specification you want to achieve, tell us what to<br />

put it on, and we do the rest. This means that your reflectance curve<br />

may vary from the one shown on this page, but the coating will<br />

meet your requirements. In addition to the standard coatings listed<br />

here, Melles Griot can supply V-coatings at any center wavelength<br />

from 193 nm to 2000 nm.<br />

These coatings are not intended for use with high-energy lasers<br />

although the Nd:YAG coatings are suitable for many mediumpower<br />

applications including diagnostics.<br />

PERCENT REFLECTANCE<br />

5<br />

4<br />

3<br />

2<br />

1<br />

normal incidence<br />

typical reflectance curve<br />

550 600<br />

650 700<br />

WAVELENGTH IN NANOMETERS<br />

Figure 5.30 Example of a V-coating for 632.8 nm /123<br />

$ Near-zero reflectance at one specific wavelength<br />

and incidence angle<br />

$ Maximum reflectance often less than 0.1%<br />

$ Standard coatings available for most laser lines<br />

$ Custom center wavelengths at specific angles of incidence<br />

available per request<br />

$ Damage threshold: 4.5 J/cm 2 810%,<br />

10-nsec pulse (361 MW/cm 2 ) at 532 nm for /122 on silica<br />

substrate; 10.6 J/cm 2 810%, 20-nsec pulse (480 MW/cm 2 )<br />

at 1064 nm for /126 on BK7 substrate<br />

Fundamental Optics Gaussian Beam Optics <strong>Optical</strong> Specifications Material Properties <strong>Optical</strong> <strong>Coatings</strong><br />

Visit Us Online! www.mellesgriot.com 1 5.23

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