Beam Waist Measurement I-Advanced Physics-Lab Report, Exercises of Advanced Physics

Download Beam Waist Measurement I-Advanced Physics-Lab Report and more Exercises Advanced Physics in PDF only on Docsity! Laser has many applications in medicine, industry etc. But laser needed in different application should of some special properties. One of them is beam diameter. In sensitive applications of laser care about beam profile is needed. Beam profile:- One of spatial characteristics of laser is beam profile. Beam profile is actually plot of variation of beam’s intensity in a plane transverse to beam. For laser beams, transverse irradiance is given by Gaussian distribution. So we can say that optical beam of laser does not have sharp boundary as Gaussian distribution does not has. But all beam’s energy is not important. We can cut beams those part which has smaller energy than its peak value. Some time it is cut at full width at half maximum of intensity. It can also be cut at 1/e 2 of its peak value. In this experiment we measured beam waist. If laser beam is not collimated i.e. beam has some convergence or divergence then its diameter is changing continuously with space. Beam divergence is described by angle θ. But in this case we can measure beam waist. Beam waist is minimum diameter of beam. From size and location of beam waist we can measure diameter at any other point by applying simple trigonometric formula. Some importance of beam waist:- In nonlinear optics, Frequency conversion efficiency of nonlinear optical material is proportional to square or cube of input intensity. To get highest possible efficiency input beam to that nonlinear optical crystal which is used for frequency conversion is made such that it has smallest beam waist inside the crystal. Beam Quality:- one of the importance of beam waist is to find beam quality from it.Beam quality parameter is M 2 . If M 2 is small then beam is good quality and has ability to be focused to a small spot. Whereas BPP is Beam Parameter Product = Radius of beam waist × divergence (Ѳ1/2). For TEM00 mode of laser M 2 =1 which is ideal value. For real case M 2 >1 and beam has poor quality in this case. Beam quality has its own importance. Beam quality M 2 =1 is required in single mode fiber. docsity.com Experiment objective:- To measure beam waist and find its location. Apparatus:- Laser source, different size filters, a convex lens, screen. Experiment procedure:- This experiment is performed as, 1. First of all align laser such that it is parallel to ground or table. As for our experiment convex lens was fixed in front of laser so in alignment we need to pass beam at center on lens. The lens is such that it can be moved horizontally and vertically for changing position of beam horizontally and vertically on screen. 2. Next to lens there is a system in which a filter is inserted or fixed in it. This system is capable of moving the filter back and forth in front of laser. Both filter and lens position is important. They should be adjusted such that laser beam can pass through it. The alignment of these components is done by adjusting positions of lens and filter from fine screws attached with lens and aperture. 3. After alignment for filter, initially of large aperture, we started from point closer to lens. As at that point, laser beam was converging, so initially there were fringes on the screen which were due to the diffraction from the edges of aperture. This indicated us that laser beam diameter is larger than size of aperture. 4. Then we moved the filter gradually away lens and we were continuously observing the fringes on the screen. There was a point on which fringes just disappeared. We noted that point and moved the filter further. Now there were no fringes on screen. Then there were another point on which fringes started again. Just before that point there were no fringes. We also noted that point. The fringes produced are called Airy patterns. 5. Form the points noted above we can measure position of beam waist. Position = docsity.com