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Chapter 20: Q31P (page 527)

Explain how beam chopping reduces line noise and noise from source drift.

Short Answer

Expert verified

The phenomenon of beam chopping line noise and noise from a source drift directed beam is investigated using sample and reference cells.

Step by step solution

01

Definition of beam chopping

  • Chopping, or periodic interruption of a light beam, has long been employed in electro-optical systems to improve the signal-to-noise ratio (S/N) of a detected optical signal (as opposed to "DC" detection approaches).
02

Determine how beam chopping reduces line noise and noise from source drift.

  • Line noise is reduced by beam chopping, but source drift noise must be explained.
  • The phenomenon of beam chopping line noise and noise from a source drift directed beam is investigated using sample and reference cells. Because the source intensity of gradual drift cancels out, the sample and reference intensities are nearly identical. More rapid flicker may not be enough to turn off the lamp.
  • It was explained how beam chopping minimises line noise and source drift noise.

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Most popular questions from this chapter

Refer to the Fourier transform infrared spectrum in Figure 20-33.

(a) The interferogram was sampled at retardation intervals of1.2260×10-4cm. What is the theoretical wavenumber range (0 to ?) of the

spectrum?

(b) A total of 4 096 data points were collected from δ=-∆toδ=+∆. Compute the value of∆, the maximum retardation.

(c) Calculate the approximate resolution of the spectrum.

(d) The interferometer mirror velocity is given in the figure caption. How many microseconds elapse between each datum?

(e) How many seconds were required to record each interfero gram once?

(f) What kind of beam splitter is typically used for the region 400 to 4 000cm-1? Why is the region below 400cm-1not observed?

Results of an electrochemical experiment are shown in the figure. In each case, a voltage is applied between two electrodes at timeand the absorbance of a solution decreases until the voltage is stepped back to its initial value at time. The upper traces show the average results for 100,300, and 1000 repetitions of the experiment. The measured signal-to-rms noise ratio in the upper trace is 60.0. Predict the signal-to-noise ratios expected for 300 cycles, 100 cycles, and 1 cycle and compare your answers with the observed values in the figure.

The variation of refractive index, n, with wavelength for fused silica is given by

n2‐1=(0.6961663)λ2λ2‐(0.0684043)2+(0.4079426)λ2λ2‐(0.1162414)2+(0.8974794)λ2λ2‐(9.896161)2

where λ is expressed in μm.

(a) Make a graph of n versus λ with points at the following wavelengths: 0.2,0.4,0.6,0.8,1,2,3,4,5, and 6μm.

(b) The ability of a prism to spread apart (disperse) neighboring wavelengths increases as the slope dn/dλincreases. Is the dispersion of fused silica greater for blue light or red light?

(a) What resolution is required for a diffraction grating to resolve wavelengths of 512.23 and 512.26 nm? (b) With a resolution of 104, how close in nm is the closest line to 512.23 nm that can barely be resolved? (c) Calculate the fourth-order resolution of a grating that is 8.00 cm long and is ruled at 185 lines/mm. (d) Find the angular dispersion (ϕ∆) between light rays with wavelengths of 512.23 and 512.26 nm for first-order diffraction (n 5 1) and thirtieth-order diffraction from a grating with 250 lines/mm and f 5 3.08.

Would you use a tungsten or a deuterium lamp as a source of 300-nm radiation? What kind of lamp provides radiation at 4-mm wavelength?
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