Pulsing Lights

[StringFever]

Hey guys,

Just a brief one - I was revising with my friends a few days ago, and our discussion steered onto the topic of spectroscopic analysis. One of my friends mentioned that he had read somewhere that a particular spectroscopic technique involved the pulsing of light. I haven't really heard of pulsed lights used to spectroscopic techniques. I was reading my notes, and the only conclusion I could come up with was that perhaps it was used in the double beam scanning spectrophotometer (a form of UV-Vis where "apparently" light is chopped/passed alternatively through two cells - a reference cell and the sample cell).

Does anyone know whether that is true?

[mystikal]

reference cell and sample cell are from Infrared Red Specs

AAS is related to pulsed light thingy

[Dark Horse]

In AAS, light is pulsed from the hollow cathode lamp so that the detector is able to differentiate between absorbed and emitted light (cos remember, while the electrons in atoms absorb the energy from the hollow cathode lamp to become excited, the excited state is unstable, so the electron returns to the ground state, emitting energy, which is of the same wavelength to that absorbed.)

Hope that helped!

[StringFever]

Thanks Dark House that did

I completely forgot that without the pulsing light, the detector would just detect 0% absorbance.

[StringFever]

Just another quickie - does pulsing light happen in UV-Vis or not?

[mystikal]

nope

[StringFever]

nope

Would you mind explaining why - because doesn't it seem logical for it to happen because it follows a similar methodology to AAS and pulsing lights happen in AAS?

[Mao]

AAS is performed with ambient light, UV vis is performed in completely isolated and dark environment, hence pulsing is not required.

AAS cannot be performed in completely isolated and dark environment because of the flame. But this is not important as atoms can only absorb specific wavelengths.