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99

Your iPhone is a pretty good grating. I just did a simple experiment with an iPhone, a green laser pointer and a sheet of graph paper. This was the result: The display of the iPhone 6 has a resolution of 326 ppi - meaning we have a "grating spacing" of 25.4/326=0.0779 mm. Different models have different resolutions - make sure you find out what your ...


8

If you've got a grating with known distance between the slits, you can use diffraction: let the light fall in perpendicular to the grating and place a screen a few meters further away. You'll find the maximum intensities (the light dots if you've got a grating with 100 or more slits per mm) under an angle of: $$\sin\theta_m = n\frac{\lambda}{d}$$ with $n$ ...


3

You haven't said precisely what instrument you are using, but what you are seeing is normal for grating monochromators. Suppose we have light of one and only wavelength $\lambda$ incident normally on a grating. Scattered light will be seen at the following angles, $\theta$: $$ d \sin \theta = m \lambda \qquad \text{for } m=0, \pm 1, \pm 2, \pm 3, \ldots$$ ...


3

First, webcams do use CCD or CMOS sensors, usually whichever chip is cheapest at the time. You can catch photons, but not reliably. In other words, for every photon that you catch, you will miss several. There will also be a noise signal, typically equivalent to many photons, Consider a CCD sensor. When a photon arrives, it may successfully excite an ...


2

You can not avoid stimulated emission! This is a fundamental mechanism that has a certain likelihood depending on the intensity of the pumping laser light. However as you say, as long as the lasing threshold has not been reached this likelihood is very small and most of the radiation is done under spontaneous emission. The ratio of the likelihood of ...


2

Laser modes are the eigen-modes of a laser resonator: only specific distributions of electro-magnetic field can "resonate" in each particular resonator. Due to the 3D nature of our space, each mode is described by 3 numbers, or indices, $m$, $n$, $q$. The latter is the longitudinal mode number, and is easy to understand: to form a standing wave, the ...


2

No, the photons do not travel in a helix, they travel in a straight line but with a phase delay that is dependent on position. Looking across the beam's wavefront there is a phase delay that is dependant on the polar angle $\theta$ around the beam axis. If we take a simple helical mode's complex amplitude as $\zeta(r,\theta,z) = u(r,z) e^{-ikz} e^{il ...


2

Infrared lasers are much more dangerous to the human eye compared to a visible laser of the same power, because infrared lasers do not trigger a blink reflex, which means the laser has much more time to damage your retina. Your other questions can be answered by reading about the many differing ways that visible and infrared light interact with matter via ...


1

A Gaussian beam has a width that changes with distance because of diffraction, which is an effect that takes place in any wave phenomenon. It has a pretty similar description to the Heisenberg uncertainty principle in QM if you're familiar with that. Namely, as the position in the $x$ and $y$ directions (with the optical axis pointing in the $z$ direction) ...



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