On Sun, Jan 6, 2013 at 10:33 AM, Simon Quellen Field <
sfi...@scitoys.com> wrote:
> In radio, you multiply the two signals. That can be done with a diode mixer.
Wikipedia and a professor I had for a radio class said the signals get
added or subtracted, not multiplied... unless by multiplication you
mean amplification...
>
> Generally you get the sum and difference frequencies, and filter for the one
> you want. Using the same frequency for both inputs gets you a frequency
> doubler, and you don't have to filter, since the difference is DC. Digikey
> has lots of RF mixers. The one I have used the most is the NE602.
>
> A beam splitter will not multiply. Otherwise you could get UV light by
> putting two beams of green light into a beam splitter. What you need is a
> medium that multiplies. The common green laser pointers use a frequency
> doubling crystal to double an infrared laser at 1064 nm into the green at
> 532 nm.
No I'm interested in wavelength doubling, not frequency doubling.
From that PhD thesis:
"A 50/50 beam splitter combines the LO beam with the signal beam
and splits part of the combined beams off to the detector and part to a
NIST traceable surface-absorbing calorimeter. "
>
> The photodiode in the article is not there to keep the brightness stable. It
> is there to detect the Doppler shift in the lidar apparatus he is working
> with. Light goes out, and is reflected back, and the signal and reflection
> are mixed, and the difference frequency is in the 10 GHz range for fast
> aircraft, which is why they need fast diodes.
>
I understand that the thesis is using 334.5nm combined with a tunable
334.5nm LO, and feeding the difference (in the low GHz) into a power
analyzer... seems just like AM radio where the difference is audio
frequency and the data, is, well audio
> Almost any non-linear response will work. You can disassemble a cheap green
> laser pointer to get the lithium niobate or potassium titanyl phosphate
> crystal out of it, and send any wavelength you want into it to get a
> doubling. The laser has to have a fairly high power in order to trigger the
> non-linear response, and the output will be much lower than the input,
> typically a tenth or less in optical power. There are losses, but the most
> obvious is the two photons in, one photon out limitation posed by simple
> physics.
>
> The crystal is inside an optical cavity (a pair of partial mirrors) since
> you'll want many passes through the crystal to get the most out of it.
>
> Check to see if the crystal and other optics in the green laser pointer
> operate in the UV ranges you are interested in. They may be opaque at those
> wavelengths.
>
> Doubling a 200 mw 405 nm violet laser gets you into the 202 nm range, and
> you still have enough power to be useful (10 to 20 milliwatts). Don't bother
> with expensive low pass filters, just aim it at a DVD and pick off the high
> frequency beam -- it will be going in quite a different direction than the
> low frequency (405 nm) beam, since it has half the wavelength. Filters are
> for when you need a compact device and you don't care much about price.
>
Again I want to double the wavelength... heterodyning 650nm with 260nm
or 280nm to increase the wavelength to a range that can make it past
the CCD window. Here are my calculations:
650nm == 4.6122*10^5 GHz
260nm == 1.1530*10^6 GHz
280nm == 1.0707*10^6 GHz
(260nm) - (650nm) == X nm
1.1530*10^6 GHz - 4.6122*10^5 GHz == 691780 GHz
691780 GHz == 433.36 nm
(260nm) - (650nm) == X nm
1.0707*10^6 GHz - 4.6122*10^5 GHz == 691780 GHz
609480 GHz == 491.88 nm
--
-Nathan