• Master or replica grating?

For many of our VUV monochromators, gratings are available either in master version or replica version. A master grating is ion etched, meaning that the grating pattern is directly included into the substrate bulk. Replica gratings are obtained from a master grating using a high precision replication process during which the grating pattern is transferred on an epoxy layer. As a consequence, master gratings are recommended for high flux applications (for example on synchrotron).

For other applications, where the flux threshold is not an issue (damage threshold for replica is 50 W/cm² maximum), replicas are a cost effective solution with a shorter delivery time compared to masters.

  • High Vacuum (HV), Ultra High Vacuum (UHV) or gas purge?

The FUV light is absorbed by air below 180 nm. Purging a monochromator with a gas (Nitrogen most of the time) will evacuate all the air contained inside and will allow working down to 160nm, even 140nm if a degassing is done.

Vacuum is necessary for VUV spectroscopy as long as you need to work below 140 nm otherwise FUV light is absorbed. The level of vacuum can be either HV (High Vacuum, from 10-3 mbar to few 10-8 mbar) or UHV (Ultra High Vacuum, from 10-9mbar to 10-10 mbar). These two levels of vacuum correspond to two different technologies: for HV version, the sealing is made by Viton gaskets while copper gaskets are needed for UHV version. Moreover, design and manufacturing processes for UHV systems need very specific attention. For example, in UHV one has to use metallic bellows or specific feedthrough to transmit a movement from the outside to the inside of the chamber. This leads to have completely different mechanical designs between HV systems and UHV systems, and makes the UHV solutions more expansive.

Most of the time, the choice between HV or UHV version is driven by the application and by the setup in which the VUV system will be connected. For example, a monochromator that is dedicated to be mounted on a synchrotron beamline may be in UHV version.

  • How to choose coating?

The coating choice will be driven by the wavelength region on which you need to optimize the intensity. Indeed, the coating has a direct influence on the efficiency. In standard, our instruments are proposed with optics coated in order to optimize the efficiency on the total spectral range. Other coatings can be done if the efficiency needs to be improved on specific regions.

  • What is the importance of the deviation angle?

The deviation angle of a monochromator or spectrograph (angle between entrance and exit arm) is a crucial point as it has a direct influence on the optic reflectivity. The higher this angle is, the higher is the reflectivity at low wavelength. For this reason, HORIBA Scientific designs grazing incidence monochromators and spectrographs to explore the EUV and Soft X-Ray regions.

  • Glossary

HV = High Vacuum
UHV = Ultra High Vacuum
TGM = Toroidal Grating Monochromator
TGS = Toroidal Grating Spectrograph
VTM = Versatile Toroidal Monograph
PGM-PGS = Plane Grating Monochromator-Spectrograph
VLS = Variable Line Spacing
DUV = Deep Ultraviolet, below 300 nm
FUV = Far Ultraviolet, 122-200 nm
EUV or XUV= Extreme Ultraviolet, 10-121 nm
VUV = Vacuum Ultraviolet, 10-200 nm
Soft X-Ray = 0.01-10 nm