# Tag Info

19

To elaborate on ratchet freak's answer; CD-ROMs work by sensing the intensity of the light reflected from the CD as it is spinning. More light being reflected stands for a 1 and less light being reflected stands for a 0 (or vice versa). One way to encode the information would be to have highly reflective surfaces for the 1's and dark patches for the 0's. ...

15

Your equation is partly correct. You've calculated the energy per photon ($\hbar \nu$), but you've neglected the number of photons. That's why the units don't match (power is energy per unit time, while you've only got energy for each photon). The ideal power (energy per unit time) depends on the area of the solar panel, $A_p$, the number of photons ...

12

There are a lot of questions in your question, and it should probably be broken up into multiple different questions. I don't want to wait until that happens though so I'll address the ones that I know the answers to. How is heat converted to an electrical signal (current or voltage)? A microbolometer is just a special case of a bolometer which ...

11

The lenses which make up the scope will always reflect some light (~0.5%). All optical materials will reflect some amount of light. This is due to the fact that light travels slower inside of the medium than it does in the surrounding air. The slowing down of a wave always results in some reflection; in optics it is governed by the Fresnel equations, ...

11

Because of optical interference. When the laser is fully in a pit or fully on land then it gets reflected cleanly and will be picked up by the sensor. However, on the transition, half the laser is in the pit and half is in the land and the reflections will interfere with each other and the sensor won't pick anything up. The pit depth and laser color (...

11

There are many reasons why highly monochromatic light, such as that emitted by a laser, is useful for delivering a large amount of power to a small spot. First of all, incoherent light sources such as a lamp are extended sources which means that they are emitting light from a piece of material which takes up a finite amount of space. When focusing this ...

10

Yes, increasing the illumination on a solar cell by using lenses or mirrors increases the electric power output. However, there are limiting factors. The efficiency of a solar cell goes down with temperature. The current stays roughly proportional to the photon flux, but the open circuit voltage goes down as the semiconductor junction is heated. Still, ...

10

The earliest CRT displays were in fact round. However, that was more due to manufacturing tradeoffs of making large glass envelopes with vacuum inside than a desire for the display area to be round. Rectangular makes more sense than round for a variety of reasons: It's what people want to look at. We use rectangular pieces of paper. Photographs are ...

7

You can easily measure the brightness of any light source in the visible with a silicon (Si) or indium gallium arsenide (InGaAs) photodiode. Both can be picked up at relatively low cost especially if buying in bulk. A photodiode works in the reverse manner to an LED. With an LED running a current through the device causes it to emit light; with a ...

7

A few points that don't fit into a comment but could help you: Get a better laser source than a 4 \$laser diode. "Better" means a laser with higher beam quality. When you look at a laser's data sheet, it should specify a value$M^2\$ or "BPP" (beam parameter product). Both these numbers are related, the smaller they are, the better you ...

6

Look at it this way: A simple compass will detect from zero to about 0.1 Hz your AM radio detects around a MHz your cellphone around a few GHz or so Radar systems anywhere from 100kHz to 1 THz Special materials can handle parts of the range from 10 microns to 0.1 micron (which includes the visible) Special crystals & other things can detect hard ...

5

Briefly: The way to distinguish your signal from any others (and incidentally get a massive gain in signal to noise ratio) is to use modulation. The simplest modulation scheme just turns the laser on and off very quickly (a few MHz) and your detection circuit (synchronized with the switching of the laser) ADDs detected signal when the laser is on, and ...

5

There are several types of ultrasound images. The most familiar for medical imaging is probably the B-mode type. This type of device uses a linear array of transducers to generate sound waves and to detect the reflected signal which is then processed to form a 2D cross-section or planar image of the tissues being scanned. When a sound wave passes into an ...

5

This could be done with a laser (and I'll give you one idea of how), but honestly you will probably be better off with an array of infrared LEDs instead of a laser. The infrared LEDs can be treated in much the same way over distances of a few meters. You would collimate each LED with a small lens and then put another lens in front of the receivers (i.e. ...

5

If you have a DMM with a uA current range, then a photodiode is the simplest detector. I get about 15 uA of current in my lab (PD area is 44 mm^2) An LED held up close can give more than 1 mA of current.

5

The technology to do what you want has existed for decades, and it is called holography. The problem with common photographic sensors and displays is that they only record/reproduce amplitude information about the light. In order to know e.g. what angle the ray came from, you need to also record the phase information of the light. This is precisely what ...

5

Acrylic and glass do let 800-900 nm IR radiation through quite well (see, e.g., here). However, your problem is probably that part of the light gets reflected at each of the surfaces. This is unavoidable, though it can be reduced by some anti-reflective coatings, but those are not available off-the-shelf as they need to be designed according to material and ...

5

Ok let me draw some pictures you right now have the following situation: If you add a convex lens to this setup you get: Which does work. However you may want to add a concave lens after the convex lens so that you can more readily adjust the beam focus and shape giving you more freedom to shape your periscope.

5

Why this is hard One micron is on the border of what is theoretically possible. You cannot create a parallel ray at this scale. One micron is almost as small as the wavelength of the light you are trying to focus, so the usual rules of optics don't apply. Lasers normally produce what is known as a Gaussian beam, and they have a distinctive shape. You can ...

4

I you look up sunspotter on the internet you get many things that look like this. While this appears to do precisely what you say you don't want, i.e. imaging the sun whith a bit of calibration it could also be used to determine alignment. Effectively this is just a folded up telescope. You could align it by firing a light source perpendicular to the ...

4

Pulsed lasers release their energy in very short pulses which can have incredibly high peak powers. A run-of-the-mill nanosecond laser will have a peak power in the multi-kilowatt range while a femtosecond laser can easily reach into the megawatt range. In contrast, CW lasers generally do not reach power levels in excess of a few hundred Watts. When these ...

4

Just a lot of pinholes (without lenses) will be enough. With a high enough density Your eyes and brain will be able to compensate the lack of complete vision pretty dang well. It'll be darker and you shouldn't go driving while wearing it but you'll be able to see enough to enjoy a party. One method could be to stretch a piece of thin black fabric over a ...

4

The simplest method will be a multi-step approach. The first step will be a defective product detection, that gathers general data about the product stream and quarantines defective products. On a parallel path, a small batch of samples will be also sequestered from the main line to be analyzed continuously for detectable defects. A laboratory analysis ...

4

There are two issues here, noise and resolution. Combining the optical images from multiple telescopes would reduce the overall noise. This is because each image is independent of the others, so all the noise would be uncorrelated. Averaging multiple images attenuates uncorrelated noise. You wouldn't really get any enhancement of resolution. There are ...

4

Large telescope mirrors are made by spinning a disc of molten glass so its surface assumes a parabolic shape, and then slowly cooling it while spinning so it retains that shape after it solidifies. Mirror blanks up to ten meters in diameter are routinely cast this way. After the mirror blank is finished, it is placed under a four-axis polishing machine ...

4

If you have access to a CO2 laser or a makerspace which has one, you can cut the profile of your light guide from acrylic sheet of suitable thickness. You don't have to have the rather expensive thick acrylic, but rather use multiple layers of thinner material. I've "extracted" the profile from your image: This particular shape would be easy ...

3

This means that the line in question can be apparent or not depending on whether the spectrum has been absorbed for other reasons. Or as Wikipedia states: ...the reabsorption near the line center may be so great as to cause a self reversal in which the intensity at the center of the line is less than in the wings. Also, there is a paper that takes this ...

3

This is just an addition to the answer of Chris Mueller. When you think about lasers, you always think about an aperture with lot of mirrors, lenses and optics in general. Lets say that you manage to create a focused (wide spectrum) beam at one point, now you want to bring it to the point of application. With a wide spectrum it won't work well, as the beam ...

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