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At first glance you might think the Fresnel lens ($area=34 \times 44 = 1496..in^2$) is better than the parabolic mirror ($area=\pi ({{40}\over 2})^2=1257..in^2$) because it is concentrating the sunlight from a greater area. But the Fresnel lens has some disadvantages compared to the parabolic mirror that out weigh the small 19% larger area.

6) The glass or plastic's index of refraction changes with frequency so different color light will be directed to different foci.

4) If the Fresnel lens is thick glass it will be very heavy to mount. If the Fresnel lens is floppy plastic, you have figure out some mounting to keep it flat or the focus will be degraded.

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At 401nm, a violet laser pointer emits a pale purple beam that is very close to the ultraviolet range. It is less visible than either red or green because it is so close to the Ultra Violet (UV) range. The violet beam is at the very far end of the visible spectrum of light so you won't be doing ray studies with this violet laser pointer. However, it is a shorter, more high energy wavelength beam that is energetic enough to be perfect for teaching and demonstrating all about fluorescence, spectroscopy, and microscopy. This is a unique and enticing piece of equipment for all types of light/matter science experiments.

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The Fresnel lens has many concentric rings of glass (or plastic) with their surfaces tilted at slightly different angles to the normal. Perpendicular light from the sun is refracted by this glass so the light is redirected toward the focus of the lens.

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Violet, the newest laser pointer color, has a stunning blue-purple glow at 401nm and is used in spectroscopy, fluorescence, microscopy, and more!

I want to make solar concentrator which can reach 2000F or above temperature at focussed spot, so I came across parabolic mirror and fresnel lens but I can't decide which one is better. Also I will be using heliostat and I want to know which one of them is easier to be added with heliostat to track sun, so which one is better for my applications?

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So the answer is not clear. For a first try I'd be inclined to go with the Fresnel lens, just because it's safer to mess with the target. With a mirror, if you try to adjust the target you can inadvertently stick your hand in the beam. With a lens, it's easier to avoid that little problem.

What's your metric for better? The Fresnel lens has a collection area of about 1500 square inches, while the mirror is about 1250 square inches. $$A_{mirror} = \pi r^2 = 1256$$ $$ A_{lens} = length \times width = 1496$$Depending on the Fresnel material, it may or may not absorb significant amounts of IR. The mirror will also get less power than the area allows if used on-axis, since the target holder will block some sunlight. You can get around this by using the mirror off-axis, but then the sharpness (and brightness) of the sun's image on the target will be degraded. Big plastic Fresnel lenses are pretty good concentrators, but not perfect.

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Built to Last- We select only the best quality lasers with proper IR filtering. Production of the Violet laser pointer is done in clean rooms that protect the laser diode from damage by dust or moisture. These lasers are aligned by experienced engineers who check several critical points during assembly to ensure reliability. This increases the life expectancy of the laser relative to cheaper versions.

The bottom line is, go with the parabolic mirror. It will direct more sunlight to a tighter focus than the Fresnel lens...but be extremely careful to stay away from the focus and not burn yourself.

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Violet, the newest laser pointer color, has a stunning blue-purple glow at 401nm and is used in spectroscopy, fluorescence, microscopy, and more!

5) The glass or plastic will transmit a narrower band of the sun's frequencies than the silvered metal mirror of the parabola will reflect.

3) The transition of glass from one ring to the other is not perfectly sharp and area is wasted from an angle of glass that doesn't direct light to the focus.

Yes, for gathering bulk sunlight the lens. For virtual reality cockpit simulators that use a small footprint, using a silvered beamsplitter and concave mirror reduces the chromatic and other distortion. The Lens are cheaper. The larger optically perfect lens will cost more. If it is quality, go with mirrors. If it is just concentration of sunlight to a target, the Lens might be cheaper for the short run.