I don't know about simulating it using comsol. However,  you need to provide certain information about the current radiation system:

1 . what will the mirror reflect ? ex: normal sun rays with certain radiation wave lengths, gamma, infra ..etc

2 . the focal point material properties: absorptivity,  reflectivity and emissivity regarding concentrated wave length.

3 . the current climate condition of temperature, pressure,  wind speed, to determine the heat lose and apply the laws for thermodynamics equilibrium

Thanks Mr. Khaled 

In my Scenario I am looking for 

1. Normal sunlight 

2. as for focal point material I am flexible to try any material as long as I can achieve maximum temperature. 

3. normal clear sunny weather 

can you please suggest any software or equations I can use to simulate these conditions .... 

first of all for the software, I suggest using Matlab package,  its simulink can become a little more handy regarding its flexibility.

You can check the two links which will explain to you more about calculations, long story short:

# for calculating the heat gain:

1. The spectrum of the sun radiation is close to that of the black body, So, you can treat it as a black body.

2. apply plank's law to calculate the energy emitted from the whole sun, then using the sun surface area, earth surface area, angle of incidence, atmospheric filteration, you can calculte the thermal energy by radiation that will be located on the mirror surface area.

3. assuming all the solar radiations will be concentrated and propagating in a certain direction "theoriticaly not true" you will multiply the radiation amount by the difference in the surface area's between the mirror and the focal point. 

4. the amount of heat gain will be regarding the focal point material absorptivity and reflectivity. 

#The heat loss will be a transfere function of heat loss by conduction from the focal point to the surrounding air take in consederation the surface area of the focal point material,  the air temperature,  wind speed ..etc.

After determining the heat gain/loss, you can now apply thermodynamic equation to determine the dT/dt and hence get the focal point temperature through the whole day

#If I had some free time I would have constructed the whole model for you, However, I am currently busy with my Phd subject. 

Regards,

https://www.google.com.eg/url?sa=t&source=web&rct=j&url=http://www.eeh.ee.ethz.ch/uploads/tx_ethpublications/Zapata_Riveros_Efficient_heating_Taking_into_account_the_working_temperatures.pdf&ved=0CDkQFjAIahUKEwjmrpmmueHGAhWB3iwKHTOrBnY&usg=AFQjCNGAUhxMmyqS6NYboVefB49GH28JHw

physics.stackexchange.com/questions/67380/how-to-calculate-incident-solar-energy-on-earth-in-a-given-day-with-a-spectral-f

check that out, to give you an idea

piserjournal.org/wp-content/uploads/2014/12/V16-165-167.pdf

I believe that the recently added "Ray Optics" module of COMSOL may model such type of problem. It has the capability to couple geometrical optics with heat transfer. Have a look at example models from their website:

http://www.comsol.com/models/ray-optics-module

@ Mr Ashish : I have been looking at the COMSOL example of solar dish 

can you please help in how does it specify the sunlight strength i.e. differenciation between sunny and cloudy day or by air temp of any particular day