200mm focal length aberration corrected spectrometer

UHV Normal Incidence Off Plane Eagle Monochromator

McPherson Normal Incidence Monochromator (NIM) as built for the Chemical Dynamics research team at the Lawrence Berkeley National Lab Advanced Light Source (ALS). At ALS it is called 'beamline 9.0.2.' It is a very productive beamline and has been used for a great deal of experimental work. McPherson provided this 6.65-meter focal length off-plane monochromator complete. It includes precision slits that may be rotated about the optical axis and real-time, laser interferometic feedback of grating rotation and focus position. The grating translates over a distance greater than 1-meter to maintain focus at a selected wavelength.

McPherson Normal Incidence Monochromator PDF Data Sheet


Additional Information:

Optical DesignAberration Corrected Seya-Namioka
Angle of Incidence32 degrees
Focal Length200 mm
f/no.4.5
Wavelength Rangerefer to grating of interest for range
Wavelength Accuracy+/- 0.10 nm (with 1200 g/mm grating)
Wavelength Reproducibility+/- 0.05 nm (with 1200 g/mm grating)
Grating Size40 x 45 mm (single kinematic grating holder, turret optional)
SlitsContinuously variable micrometer actuated width 0.01 to 3 mm. Settable height.
VacuumHigh vacuum 10E-6 torr standard, UHV optional
Focal Plane25 mm microchannel plate or direct detection CCD


Performance with various diffraction gratings:

Grating Groove Density (g/mm) 2400 1200 600 300
Spectral Resolution (nm,FWHM) 0.05 0.10 0.2 0.4
Dispersion (nm/mm) 2 4 8 16
Wavelength Range up to (nm) 225 550 1100 2200
Holographic Optimization: (nm) 80 140 140 140
140 300

* gratings work best from 2/3 to 3/2 the optimized wavelength

Outline Drawing In Progress

McPherson Normal Incidence Monochromator

Modes of Operation

Model 234302 variants

Select Publications

Abstract: We present here the assignment and simulation of rotational transitions for the H2+(X 2Σg+, v+, 2, 9 and 11) vibronic bands using the Buckingham–Orr–Sichel (BOS) model. The simulation shows that perturbation of PFI-PE rotational line intensities due to near-resonance autoionization decreases as v+ increases. Experimental rotational constants for H2+(X 2Σg+, v+, 2, 9 and 11) are determined with higher accuracy than those obtained in previous He I and Ne I photoelectron studies. In agreement with previous experimental and theoretical investigations, only the ΔN=0 and ±2 rotational branches are observed in the PFI-PE spectrum for H2.
S. Stimsona, Y. -J. Chena, M. Evansa, C. -L. Liaoa, C. Y. Nga, C. -W. Hsub and P. Heimannb
Abstract: The technique of pulsed field ionization–zero kinetic energy photoelectron spectroscopy, typically applied to the investigation of ionic states of atoms and molecules resulting from single electron excitation, has been used to probe the correlation satellite states of xenon between 23.6–24.7 eV. The resulting spectra show the formation of clearly resolved satellite states with intensities of a similar magnitude to that of the 5s5p6 2S1/2 ionic state. This technique can be extended to other atomic and molecular species to obtain the positions and cross sections for the formation of such states.
R. C. Shiell, M. Evans1, S. Stimson1, C-W. Hsu2, C. Y. Ng1, and J. W. Hepburn
Abstract: We show that by scanning the frequency of a single mode infrared (IR) optical parametric oscillator (IR-OPO) laser to excite the molecular species of interest and fixing the frequency of a vacuum ultraviolet (VUV) laser to photoionize the IR excited species, high-resolution IR spectra of polyatomic neutrals can be obtained with high sensitivity. The fact that this IR-VUV-photoion (IR-VUV-PI) method is based on VUV photoionization probe, and thus, allows the identification of the neutral IR absorber, makes it applicable for IR spectroscopy measurements of isotopemers, radicals, and clusters, which usually exist as impure samples. The highly resolved IR-VUV-PI measurements achieved using the single mode IR-OPO laser have made possible the selection of single rovibrational states of CH3X (X = Br and I), C2H4, and C3H4 for VUV-pulsed field ionization-photoelectron (VUV-PFI-PE) measurements, resulting in rovibrationally resolved photoelectron spectra for these polyatomic molecules. These experiments show that the signal-to-noise ratios of the IR-VUV-PI and IR-VUV-PFI-PE spectra obtained by employing the high-resolution IR-OPO laser are significantly higher than those observed in previous IR-VUV-PI and IR-VUV-PFI-PE studies using a low-resolution IR-OPO laser. Further improvement in sensitivity of IR-VUV-PI and IR-VUV-PFI-PE measurements by using the collinear arrangement of IR-VUV lasers and molecular beam is discussed.
Xi Xing, Beth Reed, Mi Kyung Bahng, Peng Wang, Hin Koo Woo, Sun Jong Baek, Chee Shing Lam and Cheuk Yiu Ng

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