MS257 ¼ Monochromator/Spectrograph with 77722 Motor Driven Slit Assembly
The Oriel® MS257 1/4m monochromator is a high performance instrument with features and benefits making it ideal critical applications and extended wavelength range scanning. The MS257 holds up to four diffraction gratings, and users can choose among many available gratings operating from 200 nm to 20 um. The instrument may be set up to automatically selects gratings, filters, filter wheels, input and output ports during scan. Contact Newport for assistance with configuring this monochromator.
Two grating holder options are available for the MS257. Users may select single grating mount model 77706 and one diffraction grating. This is the most economical choice, but does not allow one to have additional gratings installed later. Newport also offers the very popular patented model 77708 quadruple grating turret assembly. The 77708 may hold between one and four gratings and allows users to perform scans over a broader wavelength range than other monochromators. If less than four gratings are installed in the 77708, the unused mounting locations may be utilized later without the need to purchase another grating holder. Many standard Diffraction Gratings for Oriel MS257 Monochromator and Imaging Spectrographare available for installation onto either grating holder. Newport offers a wide selection of MS257 gratings to cover the UV, VIS and NIR wavelength regions. The gratings are installed and aligned by Newport, followed by calibration of the MS257. For custom grating designs, or special coatings such as gold or AlMgF2, please contact a Newport sales engineer for more information.
The MS257 is designed around an asymmetric in-plane Czerny-Turner configuration, with an input F-number of 3.9 to provide highly efficient throughput. The input and exit focal lengths are 220.0 and 257.4 mm respectively. The dispersion is twice that of a 1/8m monochromator. The MS257 is designed to eliminate stray light caused by reflections from a detector window or optics internal to the instrument. This is critical to achieving high performance, as stray light could potentially be re-diffracted and affect the spectral purity of the output. The reflectors inside the MS257 are coated with AlMgF2 to maximize UV efficiency. For gold-coated reflectors, which are used to enhance IR efficiency, contact a Newport sales engineer for more information.
Two MS257 monochromators, configured with identical gratings and three slit assemblies, may be coupled in tandem and controlled via RS232 connection. These double monochromator configurations are assembled in either a subtractive or an additive configuration, using kits 77715 and 77719 respectively. A mechanical assembly provides light-tight connection of the two optical ports while a 27 square inch [686 square mm] baseplate holds the two units in stable alignment. To configure a complete MS257 double monochromator system, contact one of Newports technical sales engineers for assistance.The most significant advantage of using a double monochromator system, in either configuration, is low stray light. Stray light is any radiation, other than the wavelengths of primary interest, which passes through the monochromator to the detection system. Although the MS257 has very low stray light compared to other 1/4 m monochromators, some applications may require even tighter specifications. Subtractive dispersion refers to the homogenizing of the spectrum that occurs within the second monochromator. Usually, the output band of a monochromator is a narrow slice of spectrum, changing slightly in wavelength from one side of the band to the other. In a subtractive dispersion configuration, the spectrum passed through the central slit by the first monochromator is mixed at the exit slit of the double system. The output spectral band from the first monochromator is dispersed again by the second monochromator. Ignoring all aberrations, an additive double monochromator should provide twice the dispersion of each single monochromator. That is to say, a double 1/4 m monochromator should have dispersion equivalent to a 1/2 m monochromator using the same grating. In practice, this is never quite possible because system aberrations, alignment, and synchronization slightly deteriorate the resolution of a double monochromator. The resolution limit of an additive double monochromator is slightly better than a single monochromator.
The MS257 is designed with one input port and up to two output ports, designated as axial and lateral ports. The axial port provides the greatest throughput and does not require additional internal accessories to utilize it. The lateral output port allows the greatest flexibility when mounting a detector or other components outside of the instrument. Using both output ports is very convenient, where different detectors can be simultaneously for extended range scans without needing to break down and reconfigure the setup.Newport installs the necessary internal reflector and individually calibrates all output ports to be used with the instrument. To use only the lateral output port, the 77718 side exit mirror is required inside the instrument. To use both output ports, Newport will install the 77716 motorized output mirror into the MS257. The highly reproducible mirror position is controlled by software, an optional hand controller or low level commands. The output port can be selected at any time, or can automatically be chosen for a specific wavelength range. Newports motorized beam steerer, model 77765 , may be coupled to the input port of the MS257. This allows two light sources to be utilized with the instrument, complementing the extended range capabilities of this instrument. As an example, a quartz tungsten halogen (QTH) source may be used with a deuterium source for UV light. A TTL signal provided by the MS257 controls when to change the mirror position.
The MS257 controls up to two optional filter wheels, model 77737 . Each filter wheel holds up to five 1-inch [25.4 mm] diameter filters, with a 0.92-inch [23 mm] clear aperture. Wavelength changeover points can be loaded into MS257 so the appropriate filter is automatically selected for any wavelength. This is of particular importance during a broad spectral scan, to block multiple orders and residual stray light. Newports Colored-Glass Alternative Filters are an excellent choice when selecting order-sorting filters. The filter wheels are externally mounted to the MS257.
Newport installs the shutter inside the MS257 input port. Two shutters are available, depending on the application. Both shutters are normally closed. They can be controlled through the MS257 command language, utility software, optional hand controller,TracQ Basic Data Acquisition and Radiometery Software or via an externally applied TTL signal. The shutter can be closed for dark scans and dark current measurements. The 77755 is a solenoid driven shutter. This shutter automatically closes when changing gratings and filters in order to protect the detector from possible high light intensities at various grating angles - particularly the zero order white light. For high repetition rate, short exposure applications, choose the 77717 fast shutter. This shutter may be run in short bursts at repetition rates as high as 40 Hz, with exposure times as short as 5 ms. A synchronizing output signal is available from the fast shutter for very precise timing of external events. The 77717 fast shutter does not automatically react to grating changes.
Fixed slits should be used for the utmost accuracy and repeatability, especially at high resolution. Fixed slits are the best option when only a few slit sizes are required, as they are less expensive. The fixed slits slide into the model 77721 holders located at the input and output ports. The width and height cannot be adjusted, but may be individually replaced with other slit sizes. Individual fixed slits are required and sold separately to allow customized choices based on the needs of the application (see accessory section). Order two identical fixed slits and holders for single output port models, and three fixed slits with holders for dual output port instruments. The slit width is one of the factors determining the resolution and throughput of the instrument, with a narrow slit providing higher resolution and lower throughput.
The 74002 micrometer adjustable slit offers flexibility and high throughput, but is not as accurate or repeatable as a fixed slit. The micrometer adjustable slit assembly is continuously variable from fully closed to 3 mm width. A height adjustment slide allows variation in the height from 2 to 15 mm. This type of slit is designed primarily for versatility and convenience in changing resolution and throughput. Order two micrometer adjustable slits for single output port models, and three slits for dual output port instruments.
Two motorized slit designs are available for use with the MS257. Order two micrometer adjustable slits for single output port models, and three slits for dual output port instruments. The slit widths can be set using software, low-level commands or optional hand controller in order to maintain a consistent bandpass over the entire operating range of each grating. The MS257 adjusts the slit widths for each data point.The model 77722 motorized slit assembly uses a micro-stepper motor to control the slit width from 4 um to 2.0 mm, in 2 um increments. Slit height is fixed at 15 mm. The model 77738 motorized slit assembly provides improved throughput and resolution and a 20 mm slit height. This is achieved by designing the 77738 using curved slits to compensate for the inherent bending of the entrance-slit image.
The MS257 is equipped with both a USB and RS232 port. When two MS257 instruments are coupled to form a double monochromator, RS232 communication is utilized. The model 77793 external IEEE-488 interface, ordered separately, is required for GPIB communication. Auxiliary input and output connectors are located on the back panel of the instrument for TTL signal control of select functions.LabVIEW based utility software is included at no extra cost with the MS257 to control both the monochromator and filter wheel accessory. An intuitive command set is provided for those wishing to create their own programming. Newports optional TracQ Basic Data Acquisition and Radiometery Software coordinates the operation of a single MS257 monochromator and popular detector instruments.For those who do not wish to use a computer, for either convenience or security concerns, Newport offers the optional model 77709 hand controller. The backlit LCD display provides information on the grating selection, active filter position, current wavelength, shutter status and more. Using the hand controller is intuitive and provides access to nearly all the functionality of the MS257.
The optional 77775 mounting plate can be used to secure the MS257 to an inch or metric optical table. The ability to mount the instrument simplifies setup and alignment of the optical system. The mounting plate also helps ensure consistent results over time, as the instrument cannot be accidentally moved out of position. The plate adds 0.38 inch [9.6 mm] to the optical height.
These instruments continue to function for many years. With proper care, they only require periodic maintenance to ensure gears are lubricated, spring tension is correct, etc. It is suggested to send the instrument to Newport anually for recalibration, in order to meet its performance specifications. During recalibration, the instrument is thoroughly examined and routine maintenance services are performed. In addition to this service, Newport is also able to reconfigure the grating selection, slits, shutter and output mirrors if desired. Contact a Newport customer service representative for more information.
* At blaze wavelength.** Across a 1 inch array, with grating centered at blaze wavelength.*** The primary wavelength region is where the grating efficiency is ≥20% and within the mechanical limits of the instrument.
The specifications for the 77781 monochromator were determined while using a 1200 line/mm grating and 10 µm x 2 mm slit, with the instrument set to 546 nm.