Accuracy (Wavelength) - The difference between the actual (true) wavelength and the wavelength setting. Expressed in units of wavelength (i.e. nm, µm, etc.) or as a percentage of wavelength setting.

Blaze Wavelength - The concentration of a limited region of the spectrum into any order other than the zero order. Blazed gratings are manufactured to produce maximum efficiency at designated (blaze) wavelengths. The blaze wavelength is dependent on the groove geometry and is the wavelength at which the grating is most efficient. The grating's efficiency decreases further away from the blaze wavelength which is the reason multiple gratings with different blaze wavelengths are required to cover wide wavelength ranges.

Ruled Diffraction Grating - Disperses a beam of radiant energy of mixed wavelengths into its spectral components. It consists of a glass substrate carrying a layer of deposited aluminum that has been pressure-ruled with a large number of fine equidistant grooves, using a diamond edge as a tool. Light falling on such a grating is dispersed into a series of spectra on both sides of the incident beam, the linear dispersion being inversely proportional to the line spacing. By proper shaping of the diamond edge, however, the grooves can be formed in such a way as to concentrate most of the energy into a narrow range of angles; such a grating is said to be blazed. Plane gratings require additional optics to focus the spectral lines.

Holographic Diffraction Grating - This is similar to a ruled grating except the grooves are produced using holographic techniques rather than a diamond tool. The resulting sinusoidal groove shape can then be blazed by etching the grating at the desired angle with an ion-beam. Holographic gratings tend to have less stray light associated with them than ruled gratings and are commonly used in UV measurements.

Dispersion - Defines the extent to which a spectral interval is spread out across the focal field of the monochromator and is expressed in nm/mm. It is associated with the monochromator's ability to resolve fine spectral detail. Dispersion is inversely proportional to the density of the grating's grooves/mm. The dispersion (nm/mm) multiplied by the slit width (mm) yields the monochromator's approximate HBW.

Grooves/mm (g/mm) - The density of equidistant grooves or lines on the grating. The greater the g/mm, the better the dispersion.

Half-Bandwidth (HBW) - The full width of the bandpass at half-power of the monochromator. Can be specified in either wavelength units or in percent of center wavelength. The HBW is also commonly referred to as the full width at half maximum (FWHM). The HBW is calculated by multiplying the dispersion factor by the slit width.

Order - A grating blazed in first order is equally blazed in higher orders. For example, a grating blazed at 600 nm in 1st order is also blazed at 300 nm in 2nd order and so on. The maximum efficiency for each of the higher orders decreases as the order increases. The effect of higher order flux is normally eliminated by the use of "cut-on" blocking filters.

Precision (Repeatability) - The accuracy to which a wavelength setting can be repeatedly set. Can be specified in either wavelength units or in percent of wavelength.

Step Resolution (Wavelength) - The minimum adjustable wavelength increment effectively achieved by the wavelength drive mechanism. This is sometimes referred to as the minimum scanning or stepping increment.

Stray Light - Radiant flux at the exit slit which is outside the normal bandpass of the monochromator caused by either a) random scatter from mirrors, gratings, etc. or b) directional scattered light such as reflections, re-entry spectra, grating ghosts and grating generated focused stray light.

Refer to the OL Series 750 Catalog (Bulletin 200) for more information. (Available upon request only ).

OL 750-C Controller

The OL 750-C Controller houses all data acquisition and control electronics. Communication with the host computer is through an RS-232 interface (IEEE-488 is optional). The OL 750-C consists of an integral enclosure containing a 32-bit microprocessor and associated electronic circuitry. It performs monochromator control, detector selection/interface and signal processing. Depending on the options selected, the OL 750-C may also contain one or more signal detector systems, TE cooler circuitry and/or PMT high voltage supply. Located on the rear panel of the OL 750-C Controller are three operation status LEDs. The state of these LEDs indicates the operational integrity of the controller. The OL 750-C is entirely computer operated and does not require manual operation of any controls. All commands are issued through the communications interface.

Refer to the OL Series 750 Catalog (Bulletin 200) for more information. (Available upon request only ).