On Thu, 28 Aug 2014 10:08:12 EDT, Barry OGrady
wrote:

Some can work at 2Thz.

I suspect you might mean 2 GigaHz. The PL-259 is only rated to 300
MHz:
http://www.amphenolrf.com/products/uhf.asp

Tests of the PL-259/SO-239 connectors:
http://www.hamradio.me/subjects/connectors/

I would say that it's potentially a problem above about 300 MHz:
http://www.hamradio.me/wp-content/uploads/2011/10/UHFvsOtherConnectors.png

Mo
http://www.wa1mba.org/UHFconn.htm
http://en.wikipedia.org/wiki/UHF_connector

However, lousy performance above about 300 MHz doesn't have any effect
on HF operation from 2 to 30 MHz, so they're perfectly acceptable for
use with the OP's SDR radio.

I have a HENE gas laser that connects to the
handpiece via a PL-259.

Ummm... PL-259 connectors are only rated to 500 VDC:
http://www.amphenolrf.com/products/uhf.asp
How many volts (peak) are you using to drive your laser?
1400v is typical.

--
Jeff Liebermann
150 Felker St #D http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann AE6KS 831-336-2558