bootleg2go
Enlightened
- Joined
- Jan 26, 2005
- Messages
- 440
Today I just found out a co-worker who is in my same lab, majored in optoelectronics and has worked with lasers in the past at a company called "particle measuring systems"; and had a long talk with him on the subject of lasers and such.
The first thing I found out is that I was wrong in my assumtion that the inverse squre law applies to laser/coherent light. You can calculate the power over a distance by measureing the divergence(area of illumination) at a distance. The other subject I talked with him about was the use of an LED to measure the power output of a laser like many of us are doing. Some here in the forum and myself included questioned wether the LED would provide a constant (linear) output over a large range ie would a 500mw laser that was directed into an LED provide 100 times the current output of a 5 mw. I explained the current levels were in the range of 14ua to 1000ua or 1ma. He told to me that the LED is very linear in it's operating range and will provide an output current relative the light shown on it up to a point. That point is the point of saturation, which is the point at where an increase in light power will no longer increase the current output or the other way around and increase in current through the LED will no longer increase the light output. This would mean at some point when the laser output reachs the saturation level of the LED the current produced will max out, so if the laser is powerful enough to saturate the LED, the power read from the DVM will be lower than the actual amount. Basically he said that as long as saturation does not occur and someone has come up with this divide by 2.8 to get the power in mw by using a device of known power outout like a known and measured 5mw laser, the a 500mw laser will produce 100x the current unless saturation occurs, then it will be less than 100x; however at the current levels we are looking at here <1ma no saturation should be happening yet.
To prove his point and have some fun experimenting, he is going to arrange to borrow a rather expensive power meter of some sort and well as another piece of test equipment he said was even more accurate that measured the power of a laser by the thermal energy in produces on it's sensor.
Boy this stuff is fun!!
Jack
The first thing I found out is that I was wrong in my assumtion that the inverse squre law applies to laser/coherent light. You can calculate the power over a distance by measureing the divergence(area of illumination) at a distance. The other subject I talked with him about was the use of an LED to measure the power output of a laser like many of us are doing. Some here in the forum and myself included questioned wether the LED would provide a constant (linear) output over a large range ie would a 500mw laser that was directed into an LED provide 100 times the current output of a 5 mw. I explained the current levels were in the range of 14ua to 1000ua or 1ma. He told to me that the LED is very linear in it's operating range and will provide an output current relative the light shown on it up to a point. That point is the point of saturation, which is the point at where an increase in light power will no longer increase the current output or the other way around and increase in current through the LED will no longer increase the light output. This would mean at some point when the laser output reachs the saturation level of the LED the current produced will max out, so if the laser is powerful enough to saturate the LED, the power read from the DVM will be lower than the actual amount. Basically he said that as long as saturation does not occur and someone has come up with this divide by 2.8 to get the power in mw by using a device of known power outout like a known and measured 5mw laser, the a 500mw laser will produce 100x the current unless saturation occurs, then it will be less than 100x; however at the current levels we are looking at here <1ma no saturation should be happening yet.
To prove his point and have some fun experimenting, he is going to arrange to borrow a rather expensive power meter of some sort and well as another piece of test equipment he said was even more accurate that measured the power of a laser by the thermal energy in produces on it's sensor.
Boy this stuff is fun!!
Jack
