We are having a continuous wave laser and we want to find the on-axis fluence F and total input energy E. Since it is a CW laser, there is no pulse duration. Then, how to find the fluence and Energy for CW laser?.
Energy meter generally doesn't work for continuous lasers since they are triggered at the repetition rates of the pulsed lasers. You could use a power meter to get the average power of the laser. Once you have the average power of the laser and the beam spot size (from knife edge measurement), you could calculate the fluence and energy emitted per second.
Thank you Mr. Turaga. The input power of laser is 23 mW and the beam spot size is 36.78 µm. Can u kindly let me know the formula, it would really help a lot..
You need a calibrated power-meter at 10.64 um. The products of laser mean power and exposure time gives us total irradiated energy . If you divide total energy by exposure area, then the CW-laser dose is obtained. This total energy density per irradiated area may be defined as fluence too. If you divide the CW-laser power by exposure area , then the power density is found.
Parvin sir, can you kindly tell me how to exactly measure or find the exposure area.. for examples films and liquid samples..
Do you mean that, exposure area of sample means the diameter of laser irradiated on sample???
Kindly help..
Dear Pramodini S
As the first approximation and usually adequate for many purposes, the exposure area is corelated to the laser cross-section. However, the beam profile of CW-CO2 laser is nearly Gausian (radial intensity distibution is not flat) , hence you may employ a proper beam profiler for exact measurement of laser beam profile. There are inexpensive IR cards available to demonstrate the beam crosss-section. Knife-edge is another way to determine the beam profile.
Several years ago, I and my students published an article for a novel UV laser beam-profiler as below:
P. Parvin, B. Jaleh, H.R. Zangeneh, Z. Zamanipour, Gh.R. Davoud-Abadi, "Excimer laser beam profile recording based on electrochemical etched polycarbonate", Radiation Measurements,43(20080S617-S622.
Though, It is not applicable for IR lasers, the article reviews various methods for beam profile measurements which may be useful.
Theoretically, you can calculate the energy density from:
Ed = P (W)/(U x d); in which U is the scanning speed (m/sec) and d is the spot size in (mm). The energy density Ed will be in (J/mm^2).
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