Discussion Forum

I did another test:
-I removed the rectangle and used the gaussian pulse (suppose a gaussian beam instead of the wanted tophat), as in the example. Change the expression for the analytic component into:
p_laser*gp(x-v_feed*t)*gp(y) , with gp1: the gaussian pulse.

So far it's looking promising. The results (about 1100°C) are realistic.
However, when looking at the attached image comsol2, I believe it is strange there is this variation in the max. temperature. Why is this?

So, the moving problem is fixed. But what about how to create a Top Hat distribution. Anyone an idea?

Attached the current model.

About the top hat: you can use something like p_laser*step1(sqrt((x-v_feed*t)^2+y^2)), where step1 is 1 when its argument is smaller than r and 0 otherwise, with r the radius of your top hat.

About the variation of the maximum: I have not counted but it seems like the amount of peaks in the t-Tmax graph is roughly equal to the amount of mesh elements encountered along the length of the bar. Try a finer mesh and see if it makes any difference.

Hello,

I would like to create a model in which heat transfer to the double layered material is done using a laser moving in meander shape. Can any one please help me out in creating a meander shape moment of laser for heat transfer. any ideas how to do??

with regards;
meera

If your laser would not be moving, what would be the expression for the distributed heat generation?

I now can simulate a moving laser in one direction, and oscilating in the perpendicular direction.
Thus moving in Y+ direction, at for example 200 mm/min, and oscillating in the X+ and - direction at 100 Hz. The laser in my case has a tophat power distribution. But a gaussian is of course also possible.

Is this what you mean, or what do you mean by meander?

Thank you for your response.

for example my material is of length 1cm and width 1 cm, and my laser has to move in straight line in y-direncton example 0.75cm/min and then move straightly in x-direction for example 0.25cm/min, then again move in a straight line y-direction same 0.75cm/min, then again move in x-direction for 0.25cm/min... like wise.. can you please suggest me some ideas

Maybe it is a solution to try to make different move functions, for different limits in space or time?

for example x: x-v_feed*t for [x:... to ...] etc.?

I am new COMSOL user, I am unable to understand how to represent my equation and how it reflects in the COMSOL model. First, i just tried moment in only y-direction using some examples from website, but I couldnot able to understand how it is refleting the model output.

I have seen few examples like , "Heating with a moving laser", here the laser is moving in circular direction and thez draw that circle on the wafer, but i didnt understand how they represented in the form of equatio in comsol. And another example "laser heating of silicon wafer", here the wafer is rotating and the laser is also moving along its diameter, but here also they didnt explain the moment of laser in the form of equation in comsol...

Is their any better to understand and represent the equations. I am stuck at the begining only..

Hi Meera,

Your laser light will be absorbed in the material on which it shines, acting as a heat source. The amount of heat generated is proportional to the light absorption, which is proportional to the light intensity. In the horizontal direction the intensity of your laser beam can have any distribution, although gaussian is quite common. In the vertical direction (the light propagation direction) the light will decay because of absorption. In formulas now the strenght of your heat source can be described as
A*exp(B*(-x^2-y^2))*exp(C*z), where A is related to the light intensity, B defines the width of your beam and C determines how fast the light is absorbed. exp(B*(-x^2-y^2)) is the gaussian distribution and exp(C*z) is the exponential decay.
If it is described like this the center of your beam will be where x=0 and y=0. If we now want to shift it a distance d in the positive x direction we can write it as A*exp(B*(-(x-d)^2-y^2))*exp(C*z).
If we want to shift it a distance d per second we can write it as A*exp(B*(-(x-d*t)^2-y^2))*exp(C*z).
x, y and z are defined in comsol, and t also if you do a time dependent study.
Now if you want to want the beam to move in a square you can write it as A*exp(B*(-(x-fun1(t))^2-(y-fun2(t)^2))*exp(C*z) and you have to define the functions fun1 and fun2 correctly (so first fun1 increases gradually and fun2 remains the same, then the other way around, then fun1 decreases gradually and fun2 remains the same and then again the other way around). There should be something in the comsol help/manual about defining your own functions but if you do not manage please ask.

Does this help you?

Hello,

I am trying to model a laser pulse which has a rectangular shape in 2D axisymmetric domain.
I have already modeled a Guassian shape with the equation: I0*exp(-2*(r/W)^2) as the boundary condition, where: I0: peak light intensity
r radial direction (i.e. the x axis) (Y axis is light falling on the surface)
W: beam width.
How do I express rectangular shape in mathematical expression using either step function or rectangular function?
Please suggest some ideas.
Thank you,
Ishan