IR Laser Optics - Questions

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IR Laser Optics - Questions

Which way are grooves oriented on a rectangular grating?
Can I clean the grating surface?
What is the difference between absolute and relative efficiency?
What is the damage threshold of an ML original grating?
What is the damage threshold of a wire grid polarizer?
How do I orient my grating with respect to the beam?
How do the S and P designations correlate to Perpendicular and Parallel polarizations?
Why could a gold overcoat lower the damage threshold of an ML grating even though there's less absorption for Gold than Aluminum?
What is the percent improvement in efficiency obtained by putting a Gold overcoat on an ML grating?

Which way are grooves oriented on a rectangular grating?

Unless otherwise specified, rectangular gratings are cut with grooves parallel to the short dimension..

Can I clean the grating surface?

The surface of a diffraction grating can be easily damaged by fingerprints, aerosols, moisture or the slightest contact with any abrasive material. Gratings should only be handled when necessary and always held by the sides. Latex gloves or a similar protective coating should be worn to prevent oil from fingers from reaching the grating surface. Any attempt to clean a grating with a solvent voids the Optometrics warranty. No attempt should be made to clean a grating other than blowing off dust with clean, dry air or nitrogen.

What is the difference between absolute and relative efficiency?

Grating efficiency is typically expressed as either "absolute" efficiency or "relative" efficiency. The absolute efficiency of a grating is the percentage of incident monochromatic radiation on a grating that is diffracted into the desired order. This efficiency is determined by both the groove profile (blaze) and the reflectivity of the gratings coating. In contrast, relative (or groove) efficiency compares the energy diffracted into the desired order with the energy reflected by a plane mirror coated with the same material as the grating. Be careful when comparing the efficiency curves from different manufacturers. Some publish relative efficiency data and relative efficiency curves will always give you a higher efficiency value than an absolute reading. Efficiency curves published by Optometrics at "View/Download Specific Grating Efficiency Curves" were determined using absolute efficiency criteria.

What is the damage threshold of an ML original grating?

The damage threshold of an ML grating (without any overcoats) is 1 KW/cm2 for CW lasers and 7 J/cm2 for pulsed lasers at 100 nsec pulsed.

What is the damage threshold of a wire grid polarizer?

For either a ZnSe or CaF2 wire grid polarizer, the damage is 100 W/cm2 for CW lasers and 2 J/cm2 for pulsed lasers at 100 nsec pulsed.

How do I orient my grating with respect to the beam?

Scratches or other cosmetic defects do not, unless extreme, usually affect optical performance.

How do the S and P designations correlate to Perpendicular and Parallel polarizations?

S (from the German word "Senkrenkt", meaning right angle) signifies the Perpendicular polarization. The P signifies Parallel polarization.

Why could a gold overcoat lower the damage threshold of an ML grating even though there's less absorption for Gold than Aluminum?

The mechanical characteristics of a gold layer are different than the Aluminum layer. Gold does not adhere well to most materials and, therefore, subjected to high temperatures, it may delaminate.

What is the percent improvement in efficiency obtained by putting a Gold overcoat on an ML grating?

1% absolute efficiency improvement can be expected.

Optometrics 8 Nemco Way, Stony Brook Industrial Park, Ayer, MA 01432 USA
Phone: (978) 772-1700 Fax: (978) 772-0017