What is Laser diode: Definition and 23 Discussions

A laser diode, (LD), injection laser diode (ILD), or diode laser is a semiconductor device similar to a light-emitting diode in which a diode pumped directly with electrical current can create lasing conditions at the diode's junction. Laser diodes can directly convert electrical energy into light. Driven by voltage, the doped p-n-transition allows for recombination of an electron with a hole. Due to the drop of the electron from a higher energy level to a lower one, radiation, in the form of an emitted photon is generated. This is spontaneous emission. Stimulated emission can be produced when the process is continued and further generate light with the same phase, coherence and wavelength.
The choice of the semiconductor material determines the wavelength of the emitted beam, which in today's laser diodes range from infra-red to the UV spectrum. Laser diodes are the most common type of lasers produced, with a wide range of uses that include fiber optic communications, barcode readers, laser pointers, CD/DVD/Blu-ray disc reading/recording, laser printing, laser scanning and light beam illumination. With the use of a phosphor like that found on white LEDs, Laser diodes can be used for general illumination.

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  1. Q

    I How to narrow a beam to 1 mm diameter?

    I have a collimated beam from a laser diode d= 10 mm and want to narrow it down to 1 mm. I suppose to use a lense to focus it and then use a lense to collimate it with d=1mm but this lense must have focus distance of 1 mm?? Are there such lenses? Or I must do it in other way?
  2. bmihalik

    I Using Lenses with Laser Diode Microscope to Reduce Aberrations

    I would like to build a microscope witch can be used with different monochromatic light sources (laser diodes), and this system should has small astigmatic and coma aberration, but keep the chromatic aberration property. Can I use two spherical or ashperical lenses (facing with convex side to...
  3. Aymangh994

    According to which criteria should I choose a laser diode?

    Hello everyone, I don't know which laserdiode and lens system should I choose for my Project. It is all about AFM Microscopy with a cantilever ( Length= 450 um, width = 50 um and thickness= 2um). So as you see it is not a small cantilever. As far as I Know, the larger the cantilever is, a larger...
  4. Stonestreecty

    Troubleshooting Laser Diode Circuit with Arduino and PN2222a Transistor

    Hi, all I have a circuit where the base transistor (PN2222a) leg is plugged into the pin 9 of the Arduino. When I power everything up and send the signal from the Arduino to the transistor base leg, the laser diode doesn’t light up, but my design strictly follows Complete Tech Guide to Laser...
  5. T

    Problem with this Laser diode circuit

    I have dismantled an old DVDRW drive and taken a 4-pin laser diode from it. After connecting it to two 2A batteries (red with positive, and blue with negative), the light beam is diverging, and the brightness is even dimmer than another laser diode that I got from a presentation pen. Also...
  6. R

    Best way to bond laser diode materials together

    chemical vapor deposition, Molecular beam epitaxy or magnetron sputtering What is the best way to bond GaAs to the intrinsic layer of a laser diode? I am planning on building a refactory oven on a concrete pad this summer once I clear of one side of my yard. There is just no way around it...
  7. Pattarasak

    I How to calculate the photons/pulse of Laser diode?

    Hello everyone, I'm an Undergrad and I'm trying to set the Quantum key distribution experiment by using weak laser pulses(the laser diode with attenuated filter). but I don't know how to calculate the photon number per pulse. Can anyone tell me how to calculate the photon number per pulse...
  8. U

    Direct Modulation and Photon Lifetime - Laser

    Hello, There is a thing I struggle to understand on laser physics. There is a modulation method called direct modulation for semiconductor lasers where by changing the current we modulate the light which is emitted form the laser cavity. There is a picture below It is stated in...
  9. D

    How do you calculate the power requirement for a circuit? (laser diodes)

    I have 52 laser diodes, rated 5VDC, 5mW, wired in parallel and powered by a battery, rated 5V, 2A (I measure 2.7). I'm thinking some diodes burn out because as the voltage drops, the current becomes too great. The diodes manufacturer states the maximum operating current of each diode is 20mA. I...
  10. M

    Setting up a circuit to drive a Laser Diode

    Hello fellow physics friends (alliteration: always a strong opener). I am writing today because I find myself struggling to complete something which ostensibly doesn't seem that difficult to the average physics undergrad working in a lab. However, electronics and circuits are definitely a...
  11. D

    Extreme Fiber Coupled Laser Diode Power Loss

    What could cause a laser source with fiber coupled laser diodes to have extreme loss of power? The laser diodes have a wavelength of 658nm and have an output rated at 60mW but it seems as though the optical channels actually output ranges between 58 to 70mW. During some troubleshooting I...
  12. R

    Connecting a Diode: Tips for Li-Ion 18500 Battery

    I've done my background research on this but i want to double check with others since the last time i did this i blew $30 because i shorted my diode. I got a new one but I'm really nervous about starting it up. These are the two parts...
  13. M

    Laser Beam Propagation: Calculating Power & Radius

    Hi all, I am interested in finding the power of a laser diode as function of the distance z, assuming a free space propagation. I think to have enough information to work it out but I am stacked at the moment. Given: the initial power, P0 = 1mW beam width clip (e-2 = 13.5%), wx = 3μm, wy =...
  14. G

    Laser Diode Principles: Stimulated Emission & Voltage

    As far as I understand, when forward biased voltage applied, electrons from N diffuse to P, then recombine. Since energy gap between conductive electron and hole is const => only certain wavelength photons is emitted. In gaseous lasers for example you need to gain a populational inversion...
  15. R

    Band Diagram of Multi-Quantum Well Laser Diode

    Homework Statement This isn't for a homework problem per say, though it is a coursework question. I'm writing a lab report on Multi-Quantum Well Laser Diodes and am trying to explain the basic semiconductor physics behind it. As such I need a diagram of the band structure. Homework...
  16. W

    Warming a laser diode using a thermistor

    I use a green laser pointer at night to do astronomy related work. I got a cheap $5 green laser pointer off of ebay, and when it's a warm summer night, the device works fine. However, the second it touches the cold, it fizzles out and gives me almost zero output. My idea was to use a...
  17. S

    Two questions about the dynamics of a laser diode

    I am using a laser diode to count aerosol particles flowing through a gas stream. The refracted light is being funneled to a photo-multiplier via fiber optics. When there is no gas flowing (and therefore no particles) we are seeing some strange results from the output signal of the...
  18. hagopbul

    I am buying a laser diode but cant understand some parameters

    i am buying Pulsed Laser Diode in Plastic Package 25 W Peak Power SPL PL90 and there is some parameters about semiconductors lasers... Forward current = 40 A why all this current ? then in the catalog Reverse voltage= 3 Volt then they say the Threshold current = 1A ? what is the...
  19. S

    TE / TM polarization of a Laser Diode

    I am working with a Laser Diode and I need to observe the intensity of the diode in TE and TM polarizations. the Diode is polarized in the horizontal axis (linear polarization). Is it sufficient to use a half wave plate and rotate it by 90 degrees to observe TE and TM modes? Also, what kind...
  20. F

    Fastest modulation: laser diode vs LED

    fastest modulation: laser diode vs LED... Hello Forum, in the telecomm industry, the most common and economical form of modulation is direct modulation, acting on the current operating LEDs or diode lasers. Using an external intensity modulator (OOK), like a super fast chopper, the...
  21. M

    Pulsed laser diode driver - how it works?

    Hi everyone, I've been looking at the data sheet for a pulsed laser diode driver that I've been using, and I've managed to convince myself that there's a mistake. I was hoping that if I post my explanation of how the circuit shown in the data sheet works, that you guys can either confirm that...
  22. R

    Pulsing a 2W Laser Diode w/ 26 AWG Wire - Is Gauge Okay?

    I am going to be pulsing a laser diode at around 2 Watt (room temperature) with a frequency of around 1-10 MHz. Right now I'm planning on using 26 AWG wire. Anyone have any thoughts on whether this is okay? Is the gauge okay? Since it's pulsed I assume I don't have to worry as much about heat...
  23. H

    Eye Safety: Laser Diode Recommendations

    Can anyone recommend a good laser diode that won't cause damage to the eye with prolonged exposure?