00:01
Hi.
00:02
So we are given that a gaussian laser beam with width of w is equals to 0 .5 centimeter and a planar flash front is incident on the lens with focal length f is equals to 10 centimeter.
00:22
The laser wavelength lambda is equals to 800 nanometer.
00:28
In a part, how far after the lens is beam, we are still located, as we have to find out here.
00:36
So let's get started with the concept which we are going to use here for this question.
00:44
Since we know that the rayleigh range formula, that is zr is equals to pi times of w, means width that whole square, divided by lambda.
01:00
So let's plug in the values.
01:02
Pi is a constant whose value is known to us as 3 .14 and 2.
01:07
The width is 0 .5.
01:09
That whole square divided by the wavelength is 800 nanometer.
01:14
So nano means to say 800 into 10 to the power minus 9.
01:21
So after simplifying and solving, this zr will comes nearly equals to 812 .5...