Raman_basic

Hg Lamp (position in the Raman spectrum measured with 532.07 nm incident laser)

546.074nm (482 cm-1）: ☆ (1/532.07 - 1/546.07) * 10^7 = 481.848 cm-1

576.959nm（1462⊿cm-1）: (1/532.07-1/576.96)* 10^7 = 1462.2954 cm-1

579.065nm（1525⊿cm-1）: (1/532.07-1/579.065)*10^7 = 1525.3010 cm-1

Ne Lamp

534.109nm(72⊿cm-1) : (1/532.07-1/534.11)*10^7 = 71.78450 cm-1

540.056nm(280⊿cm-1): (1/532.07-1/540.06)*10^7 = 278.058 cm-1

585.249nm(1709⊿cm-1) ☆ (1/532.07-1/585.25)*10^7 = 1707.8044 cm-1

5.Relative value of Raman shift

1. Obtain Rayleigh spectrum.

To do this, we have to remove the edge filter and insert a lot of ND filters in the optical path. We can determine the position of 0 cm-1 in the spectrum.

2. Measure a standard line.

From the difference between the Rayleigh line and the standard line, one can obtain the absolute wavelength of the incident laser. (A precise "pixel vs cm-1" relation ship at CCD should be provided a priori. )

6. Absolute value of Raman shift

We know the Hg spectrum has an energy of 1/546.074 [cm-1].　Assume we know the laser wave length precisely ( λ nm).The energy is then 1/λ [cm-1].　Then the Hg spectrum should appear at (1/λ-1/546.074) [cm-1] on Raman spectrum.

We can tune the x axis of the Raman spectrum so that the Hg peak appears at (1/λ-1/546.074) [cm-1].

The determination of the laser energy (or wavelength λ) is not straightforward (as far as I know).

The absolute value of Nd-YAG oscillating wavelength is in the literature(Rika Nenpyo). The strongest oscillating wavelength is 1064.14 nm and its second harmonic generation is 532.07 nm.

What makes the determining laser energy complicated is the temperature effect. The temperature shift of the oscillating wavelength of 1064.14 nm is -4.6cm-1 / 100℃(Shao Zhong Xing and J. C. Bergquist, IEEE Journal of Quantum Electronics vol.24, pp1829, 1988).

1064.14 nm corresponds to 9397.26 cm-1, and the shift of -4.6cm-1 by temperature increase by100℃ makes it 9392.66 cm-1 and the corresponding wavelength is 1064.66 nm.

The second harmonics of the initial laser is 532.07 nm, and that of the temperature-affected laser is 532.33 nm (red shift).

This red shift of the incident Laser causes a shift of the Hg line in Raman spectrum.

At λ= 532.07nm, Hg line appears at 481.85 cm-1.

At λ= 532.33nm, Hg line appears at 472.67 cm-1.

(Be aware that the difference is doubled (9.2cm-1) in the second harmonics.)

A shift of 9.2cm-1 is too much. But this seems unlikely in our system. The important point here is that by the temperature increase, the laser energy shows red shift, and the exact position of Hg line in the Raman spectrum moves to smaller energy.

There is a possibility that the exact position of Hg line in the Raman spectrum is lower than

481.85 cm-1 due to the higher temperature of the Laser. (There is no possibility that the exact position of Hg line in the Raman spectrum shift to higher energy by the increase of the temperature of the Laser.) This has to be in mind when one tries to calibrate theRaman peaks using bright lines.

The oscillating wavelength of laser can be measured using wavemeter, such as WaveMate Deluxe provided by Coherent.