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Lasers for medical device!

r34p3rex

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I'm back on LPF! Except this time, I'm not really looking into high powered lasers.

Long story short, for my senior design project, we're designing a low cost and portable oral cancer diagnostic device that requires several light sources of different wavelengths. The device operates on the principle of Elastic Scattering Spectroscopy (ESS).

We are actually improving on the design done last year which utilized LED's and a photomultiplier tube (PMT) to amplify the LED output (the light travels through a fiber optic cable) in order for the photodiode to detect an adequate amount of light.

There are several problems with this design:
1) PMTs are expensive. We are looking to reduce the cost of the device
2) Without a PMT, the LEDs are not bright enough for the photodiodes to make an accurate measurement.
3) PMTs do not operate linearly in that they are less sensitive to near-IR wavelengths (650nm+). Based on past research, the wavelength with the highest signal-to-noise ratio for ESS is around 680nm. Therefore, there is a larger margin of error by using a PMT in the design.

Having played with lasers in the past, this got me wondering. Theoretically, lasers should output enough light to eliminate the need for a PMT. My primary concern is that many of the diodes commonly used here on LPF are high powered. For example, the 445nm diodes operate at 300mW+. Since the laser diode output will be directed into a fiber optic cable (200nm thick) and make contact with the patient's skin, I was wondering if the high power should be of concern. I realize that only a small portion of the laser radiation will be directed into the fiber optic cable (and therefore onto the patient's skin)

1) Would de-focusing the laser reduce the amount of radiation entering the fiber?
2) What's the lowest power output you can use on the 445nm diodes?

If you have any other suggestions, let me know! Thanks in advance :D
 

Cyparagon

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There is no way you can get even a majority of the light from a common blue laser diode into a 200nm fiber. Too much power isn't a concern, anyway, because if you reduce the current, you reduce the power.
 

r34p3rex

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There is no way you can get even a majority of the light from a common blue laser diode into a 200nm fiber. Too much power isn't a concern, anyway, because if you reduce the current, you reduce the power.
Yea that's what I figured. Thanks for the confirmation :D
 




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