Wavelength Selection Homework Problem Set

This problem set was developed by S.E. Van Bramer for Chemistry 366 at Widener University.

Goal:

to introduce students to several common wavelength selection techniques

Objectives:

• Students will be able to identify the performance characteristics of different types of filters
• Students will be able to describe the tradeoffs involved in monochrometer design

Introduction:

Spectrometers typically use either a filter, which transmits a limited wavelength range, or a grating, which disperses light, to select a wavelength of light for an experiment.

Filter Questions:

Melles Griot is an optics company that produces a wide range of filters. They have information available at: www.mellesgriot.com under "optics"; "filters"
1. Compare the transmission efficiency of a colored glass VG9 green glass filter with an 03 FIV 309 bandpass interference filter at 500, 520, and 550 nm.
2. Determine what a notch filter is used for and select one that would be appropriate to use with the second harmonic of a Nd:YAG laser. A Nd:YAG laser operates at 1064 nm.
3. Sketch what you expect the transmission efficiency to be for a heat absorbing filter. Compare your expectations with a KG 2 heat absorbing filter.
4. Sketch what you expect the transmission efficiency to be for a long pass cutoff filter. Compare your expectations with a GG 400 filter.

Monochrometer Questions:

Monochrometers involve tradeoffs between the spectral range, spectral resolution, transmission efficiency, and design wavelength.
1. Use the technical information available at the ocean optics web site: www.oceanoptics.com to design a monochrometer with 1 nm resolution and a spectral range from 400 to 800 nm.
2. If you increase the number of grooves per mm, what happens to the resolution and spectral range?
3. What happens to the resolution and spectral range when the slit width is reduced?
4. Look at the figures and equations in your textbook to find the information you need to explain the relationship between resolution, spectral range, and slit width.
5. The ocean optics spectrometers use a CCD or diode array detector. What are the advantages and disadvantages of this detector when compared with a photomultiplier tube.