Talk:Terahertz time-domain spectroscopy

Discussion of the two edits made on 21 Jan.

The first edit was for the generation discussion only. The major aspect of the change was to remove the word "spark" from the discussion. A spark is conduction through an ionized gas (plasma). There are definetly no sparks in THz generation. The EM emitted from a spark gap is a good analogy for the generation method, but it is important to stress that no spark ever occurs.

I have not registered as a contributor yet (not certain how) but I am an R&D scientist building state-of-the-art THz-TDS systems. Additionally, my Ph.D. research group studied spark and arc analytical instrumentation so I am also familar with that technolgy. FYI, what is the difference between a spark and an arc? An arc is caused by the simple overvoltage of a gap. Thus, there is no precise temporal control of when the arc will occur. A spark is generated by a high voltage switch. Thus, there is very precise temporal control.

The second edit fixed some minor problems with the Genreation section and added the Detection section. This is my first pass of the Detection section so it may not be as clean as it could be.

I plan on contributing to the pulse shape / frequency content section soon.

-JSW —The preceding unsigned comment was added by 141.214.17.5 (talk • contribs) 06:34, 22 January 2006 (UTC)

You missed one thing: the short duration of the generated terahertz pulse does not require a rapid carrier trapping (or recombination) time in the substrate. A rapid increase of the photocurrent is sufficient; a rapid decrease also works but is not crucial. In fact, most practitioners of THz-TDS use semi-insulating gallium arsenide (GaAs) substrates for THz generation. In that material, the photocurrent persists for nanoseconds after optical excitation, and yet the generated THz pulse is still short. —The preceding unsigned comment was added by 70.240.180.76 (talk • contribs) 00:40, 24 January 2006 (UTC)

Yes, that is correct. I thought it might be too involved to explain so succiently. Good edit.

-JSW —The preceding unsigned comment was added by 208.178.99.146 (talk • contribs) 20:20, 24 January 2006 (UTC)

nonpolar?

The introduction says one of the advantages of the form of spectroscopy is that the radiation is "nonpolar". This term requires some elaboration. It's not clear to me what is meant, and I am more familiar with TDS than the typical reader. Spiel496 18:50, 6 March 2006 (UTC)

I would have to consider that to be an error. Which I am about to fix. There is no meaning in describing electromagnetic radiation as 'nonpolar'. —The preceding unsigned comment was added by 70.240.204.99 (talk • contribs) 03:38, 15 March 2006 (UTC)

Thz Spectroscopy =/= TDTS

Can I ask why is the Terahertz Spectroscopy completelly redirected to TDTS?!

That's ridiculous! THz Spectroscopy can be

• time domain (TDTS)
• frequency domain (FDTS)

We us broadband THz sources for time domain measuremnets (by optical rectification, photoconductive witches,...). Measurements are usually slow, lower resolution, but wide spectra. We us monochromatic (continuous wave, CW) THz sources for frequency domain measuremnets (by frequency matching - +tunable,...). Measurements are quick, high resolution in the frequency domain, but usually narrow spectra. —The preceding unsigned comment was added by 86.49.61.227 (talk • contribs) 19:57, 17 November 2006 (UTC)

Please do create new articles on Terahertz spectroscopy and Terahertz frequency domain spectroscopy as necessary! Melchoir 19:24, 18 November 2006 (UTC)

Thanks. OK, I'll do it. I don't know how to create and set them "as necessary", but they'll be created, some basic info will be added. Milan Berta 19:59, 18 November 2006 (UTC)

Removal of Surface Emission Generation

I removed the recently added reference to the 'Surface Emission' generation technique because, as far as I know, this technique is not commonly applied to spectroscopic applications. If you could provide some references to its application, I would be happy to look through them and reconsider its inclusion. ronningt (talk) 15:02, 19 July 2008 (UTC)

Diagrams

I think that we really need to show time-domain traces and spectra for a pulse transmitted through a sample, compared with a reference pulse from an empty TDS system. This will make it much easier to explain how materials can be characterised. Papa November (talk) 11:06, 17 April 2011 (UTC)

Analysis

I also think we need to include a bit of maths here... an explanation of how to calculate the refractive index/thickness, Fresnel reflectivity and Beer's Law absorption coefficient from the Fourier-transformed traces. Papa November (talk) 09:02, 27 July 2011 (UTC)

Safety

Can someone with domain knowledge speak to the information presented in this paper? http://arxiv.org/pdf/0910.5294v1.pdf