Model 77250 1/8 m Monochromator with 6025 Hg(Ar) Spectral Calibration Lamp.
For general-purpose laboratory work or academic applications, the Oriel 77250 1/8 m Monochromator is a smart and economical choice. This simple, manually operated 1/8 m instrument has good resolution, low stray light and is very versatile. A large family of slits and gratings give a wide range of bandpasses and broad spectral coverage.
The optical configuration of the 77250 is the reason why throughput is so high while stray light performance is unrivaled. Fig. 1 shows the Ebert-Fastie design with two inline slits and an out of plane grating. Having the slits opposite each other lets you mount the complete optical system on a bench or rail. Having the grating out of plane eliminates re-entrant spectra.
The excellent stray light performance of the 77250 can be judged from the measurements below.
With a Deuterium Source, a UV-VIS PMT, and Holographic Grating blazed at 250 nm (model 77296 ), measurements were made with and without a glass plate in the beam. The stray radiation with the glass in place was 0.2% of the signal recorded at 210 nm without any glass, and 0.1% of the signal recorded at 250 nm. The signal at 210 nm with the glass in place was 0.1% of the signal at 210 nm without the glass. At 250 nm, the stray light signal was only 0.025% of the unblocked signal.
Using a HeNe laser at 632.8 nm focused on the slit in an F/4 cone, the average of the stray radiation readings at 612.8 and 652.8 nm was 0.008% of the signal at 632.8 nm. In this case, the response of the detector is irrelevant as the only light detected is at 632.8 nm.
The 77250 uses a hand crank to turn the grating. A 3-digit counter displays the wavelength directly in nanometers when using a 1200 l/mm grating. A calibrated wheel marked in 0.2 nm divisions lets you position and read the wavelength to 0.1 nm. For gratings with other line spacings, multiply the wavelength on the counter by the Wavelength Counter Multiplier listed in Table 1. The readout is factory set so the wavelength indicated is correct to within 1 nm through the full range of a 1200 l/mm grating. For greater accuracy, you can reset the readout within any restricted spectral region. The precision of this instrument is better than 0.2 nm, limited by backlash.
Each grating is mounted in a protective frame. The frame has a tab for quick and easy insertion and removal without touching the surface of the grating. The following 30 x 30 mm replicated gratings are for the 77250 only; they cannot be used in any of our other Monochromators.
We offer three types of slit assemblies for the 77250 in various slit sizes. Choose the same type and size for the input and output. Our slit assemblies have a 1.5 Inch Series male flange.
This assembly uses a micrometer drive to adjust the width from 4 µm to 3 mm.
This assembly consists of a rotating disc with 8 fixed slits. A manual wheel rotates the disc, which has a positive detent for exact repeatability of slit position.
If you only need a few slit sizes, this is the most economical choice. These are precision slits fixed on a machined slide. You need the 77294 Fixed Slit Holder to hold the slit and mate it to the monochromator.
Rod mounting the 77250 allows the greatest flexibility; you can vary the optical axis height to match your source or detector. To rod mount the 77250 , order the 77387 Monochromator Mounting Plate and two Molded Composite Optical Mounting Posts.
To order a complete 77250 Monochromator, you must specify a grating and (2) slit assemblies separately.