I want to instill a laser, but I need to use lenses to focus the laser on the sample. what's the difference between 1 lense and 2 lenses, i want to get high laser intensity on my sample, how should i choose the amount of lense? Thank you very much!
Well, I’m afraid it depends. Very often the short answer is use two lenses: a pair of aspheric collimators, the second used backwards.
The longer answer is more complicated. It varies wildly depending on the description of your laser beam. Please describe your laser, in particular the output beam size, intensity profile, beam quality (or divergence) not to mention the wavelength. Then describe your desired target spot: how small of a spot would you like? How close to the target are you willing to put the last lens. Finally describe your cost tolerance. This can probably done with a few hundred dollars, but might be done better for several hundred dollars.
Since your LASER is monochromatic and you are probably on-axis, meaning the beam is going through the center of the lens, you are contending only with spherical aberration. Spherical aberration is solely attributed from the spherical curvature of the lens, which the end result is blurring of the spot at the focal plane. Because of this aberration you have four options.
1. You can use a single aspherical lens to focus your beam.
2. You can use an achromat doublet; a doublet has two lenses (four surfaces) that are adhered together and those four surfaces work to cancel spherical aberration.
3. You can use two lenses separated with an air gap; this is essentially the same as option #2. Option #2 is a better option because the glued doublet is easier to work with.
4. If you want to use a large LASER beam entering into your lens (larger entrance aperture will create a tighter/smaller focal spot), then you may want to use a combination of option #1 and #2 eliminate spherical aberration. Remember, the larger your beam is the more of the edge of the lens you will use, which means more spherical because the edge of a lens causes more aberration.
To start off, I would use a cemented doublet and face the more curved side of the lens towards the beam (try both sides). Calculate what the PSF should be (2.44*lambda*f/D) where D is the diameter of the beam entering the lens, not the lens diameter. Use a profiler (camera) to measure your actual PSF and if the theoretical and actual PSF match then you have eliminated spherical aberrations; if not then you have spherical aberration blurring your PSF and making it larger (spherical will not make the PSF to be smaller).
Hope this helps,
Logan.
If you have a laser beam diameter of no more than 3 mm, then you can use a webcam lens with its front surface turned towards the laser (this is the cheapest option). If the lenses burn out from the laser beam, it will not be so expensive.
You can use a ready-made microscope objective with the desired working length. For a thin laser beam, this may be the best option. The main thing is that the lenses of the objective can withstand the power of your laser.
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