Talk:Laser diode

LED versus laser diode

What is the difference between an LED and a laser diode? —Preceding unsigned comment added by 64.246.146.251 (talk) 23:36, 18 July 2008 (UTC)

phase coherence, is the difference between laser and normal light. At lower current/voltage, most laser diodes function as an LED until the 'lasing' happens. Phase coherence means all the light is in 'phase' so for the same amount of photons, the peak energy is bigger. It gives laser light many special properties. See: Coherence (physics). It probably should be in the intro, so great point. 184.144.115.253 (talk) 23:07, 28 February 2022 (UTC)

Laser Diode Photo #3

Regarding the visible light micrograph, I believe the picture is actually of a photodiode and not the actual laser diode.

Here's a picture of a red laser diode, taken from one of several cheap laser modules I have: http://i51.tinypic.com/wheik7.jpg Here you can see something that looks to me a lot like what that picture shows, and I'm fairly certain is a photodiode used for feedback.

http://i56.tinypic.com/2mi3hig.jpg Here's the diode in operation, with the laser diode clearly visible as the sandwich in the front.

(Moved from the file discussion page, got no response there) —Preceding unsigned comment added by 67.204.164.5 (talk) 09:35, 28 December 2010 (UTC)

I'll second that - that looks like the power sense photodiode. Awesome picture with the laser! I just took some pictures that were more illustrative than #3, but I like but I really like yours, too! Morcheeba (talk) 06:24, 27 March 2011 (UTC)

HeNe in Laserdisk players

Were Helium Neon lasers used in early CD players, or just laserdisks? --Slashme 11:12, 19 December 2005 (UTC)

If the information in the Compact disc article is correct, HeNe's couldn't have been used for CDs. the CD article says that the pits are 1/2 of the 780 nm LD wavelength, whereas the shortest emission wavelength from the HeNe is 633 nm. Presumably Philips' earliest audio laser discs would have been designed for HeNe's but the discs made for those systems wouldn't be compatible with today's CDs. If it's true (please cite sources), it might be reasonable to say that "laser diodes have replaced HeNe lasers in laser disc players, which were originally designed for the larger gas lasers" or something like that.

--The Photon 04:28, 20 December 2005 (UTC)

That's a very far fetched interpretation. While HeNe lasers almost certainly have been used in one way or another to develop the technologies that enabled CD consumer devices and to study prototypical data storage and retrieval in test systems they would have never been used with CDs simply because they have not been miniaturized from their bulky fragile implementations into something of practical relevence to a consumer product.

Laserdisc players were mass produced (more or less) with HeNe's. So it wasn't at the time impossible in principle to make a HeNe-based consumer device. The question, not yet answered, is, have Laserdisc players been built with diode lasers replacing the HeNe's? -- The Photon 01:58, 5 August 2006 (UTC)

Multi-wavelength Diode Lasers

With the advent of BluRay and HD DVDs there is a need for multi-wavelength diode lasers to read/write not only these discs but also red DVD and IR CDs. I think these are for now hybrid modules with multiple laser diodes and detectors on an optical pick-up. While these are magnificent examples of miniaturisation they are delicate and yields muct be low. Anyone have any info on what the industry is doing about this?

I am sure they will ultimately be monolithically integrated but this is a tall order given how dissimilar the laser structures are. This may be a stumbling block for the expansion of the HD DVD market IMO. Royzee 12:36, 1 February 2007 (UTC) Feb 1 2007

How it Works

This article does not tell how the diode laser actually works... what is the process in which a laser beam is created in this setup that is different than a regular diode... —The preceding unsigned comment was added by 84.94.198.180 (talk) 23:40, 8 February 2007 (UTC).

I guess the above question (not by me) is answered in the article by now. Another one: Why is the light polarized? Polarization is already mentioned twice, but it is no clear how a typically broadband laser diode can always lase in one polarization. Arnero (talk) 16:35, 12 March 2008 (UTC)

Although polarised, it isn't very polarised. 86.182.66.217 (talk) 13:11, 27 May 2010 (UTC)

When light reflects off a dielectric surface, it becomes partially linearly polarized. Glass is a dielectric surface, as is the surface of a semiconductor. The amount of polarization depends on various factors that I don't know entirely off the top of my head, but one factor is the number of times the beam of light bounces off the dielectric surface. In many lasers, the beam bounces many times off the end pieces before it eventually escapes to form the output beam. Note also that when a photon stimulates the release of another photon, the stimulated photon will have the same polarization as the stimulating photon. So, a laser beam that is composed largely of stimulated photons will be more polarized than a laser beam that is composed largely of spontaneous photons.

http://www.rp-photonics.com/polarization_of_laser_emission.html

http://www.princetel.com/tutorial_pigtailing.asp

Pooua (talk) 09:50, 30 August 2010 (UTC)

I believe that clarification (preferably visual but possibly written) is needed to explain the "checkerboard-like" pattern of direct-bandgap transistor. I'm afraid it's a bit confusing... Any better explanations should be included! Ivangiesen (talk) 16:59, 14 February 2019 (UTC)

The three pictures of more advanced laser diodes are excellent. If anyone can find or make a similarly high quality picture for simple laser diodes, it would enhance the unity and quality of this article. Ivangiesen (talk) 17:12, 14 February 2019 (UTC)

Efficiency

We need figures for voltage, current, watts, lumens, and lumens per watt for typical devices.-69.87.203.48 20:53, 19 May 2007 (UTC)

And general numbers too, like "up to 50% of the electricity used will be converted to laser light". I know that the high power laser at the bottom of the page, which is from a NIF-offshoot project, is about 12% and is expected to scale to 20% in the short term. That's about the only number I've seen though. Maury 01:36, 11 October 2007 (UTC)

Yes, I came looking for limitations of laser diode versus some of the higher power lasers. CO2 and crystal lasers are for class 4 applications like laser cutting. I don't think a laser diode can be used for those applications. 184.144.115.253 (talk) 23:14, 28 February 2022 (UTC)

Merge from Distributed feedback laser

• Oppose - this article (laser diode) is already reaching the point where if it gets any larger, it should be split into sub-articles. The DFB article could stand expansion, with the current small paragraph here pointing to it. --Bob Mellish 17:13, 30 November 2007 (UTC)
• Oppose - quantum cascade lasers commonly use distributed feedback to achieve single mode lasing. Distributed feedback is a general technique, not specific to diode lasers.--Miles Weida (talk) 22:07, 25 March 2008 (UTC)
• Oppose - The DFB laser is an important type of laser diode with unique and highly useful characteristics. A complete and informative encyclopedia article treating DFB lasers should be constructed to appear in Wikipedia -- Jabeles (talk) 19:15, 23 May 2008 (UTC)

1st class article

This article, particularly the three photos at the top right, are of excellent encyclopaedic value. I suggest we promote this idea for more articles. --Wierdy1024 (talk) 15:07, 28 July 2009 (UTC)

Distinguishing Crystalline Lasers

A paragraph in the article currently states that "As charge injection is a distinguishing feature of diode lasers as compared to all other lasers, diode lasers are traditionally and more formally called "injection lasers." (This terminology differentiates diode lasers, e.g., from flashlamp-pumped solid state lasers, such as the ruby laser. Interestingly, whereas the term "solid-state" was extremely apt in differentiating 1950s-era semiconductor electronics from earlier generations of vacuum electronics, it would not have been adequate to convey unambiguously the unique characteristics defining 1960s-era semiconductor lasers.)" However, these statements are false or misleading, as:

1) diode lasers can (in some cases) be optically pumped; they are not all charge-injected.
2) diode lasers are, in fact, distinguished from solid state lasers, by designating diode lasers as semiconductor lasers. The curricula under which I received my AAS in Laser Electro-Optic Technology so distinguishes between the two types of lasers. So, a ruby laser is a solid state laser, but a laser diode is a semiconductor laser.

Sam's Laser FAQs has a useful reference: http://www.repairfaq.org/sam/laserdio.htm#dioopsl Pooua (talk) 09:38, 30 August 2010 (UTC)

To MaterialScientist:

Are all these also book and paper promotions?

   * B. Van Zeghbroeck's Principles of Semiconductor Devices( for direct and indirect band gaps)
   * Saleh, Bahaa E. A. and Teich, Malvin Carl (1991). Fundamentals of Photonics. New York: John Wiley & Sons. ISBN 0-471-83965-5. ( For Stimulated Emission )
   * Koyama et al., Fumio (1988), "Room temperature cw operation of GaAs vertical cavity surface emitting laser", Trans. IEICE, E71(11): 1089–1090( for VCSELS)
   * Iga, Kenichi (2000), "Surface-emitting laser—Its birth and generation of new optoelectronics field", IEEE Journal of Selected Topics in Quantum Electronics 6(6): 1201–1215(for VECSELS)

If you censor one you should censor them all. The book in questions is quite relevant to the discussion albeit the link to the book page might be directed to Google. Signed by Corrigendas. — Preceding unsigned comment added by Corrigendas (talk • contribs) 01:44, 14 December 2010 (UTC)

Mention of where hobbyist can get low power laser diodes

Folks:

Is it at all reasonable for an article to mention places where a hobbyist can get really low power laser diodes (under 100 microwatts)? I am a led jewelry artist and I am having trouble finding a source of very low power laser diodes.Allyn (talk) 05:34, 30 October 2011 (UTC)

corrections needed in Common Wavelengths

This article currently states:

• 635 nm – AlGaInP better red laser pointers, same power subjectively 5 times as bright as 670 nm one
• 640 nm – High brightness red DPSS laser pointers
• 657 nm – AlGaInP DVD drives, laser pointers
• 670 nm – AlGaInP cheap red laser pointers

There are no cheap laser pointers at or near 670 nm. There are only expensive 671nm DPSS laser pointers in the $500 - $4000 price range (Dragon Lasers, Laserglow). Cheap red laser pointers are nominally 650nm (actual 653-4) (spectra of red lasers, eBay). The part about 635 being five times as bright as 670 should be changed to a comparison between 635 and the nominal 650 of common cheap laser pointers, maybe with something in parentheses for actual rather than nominal wavelengths (chart of scotopic spectral sensitivity curve CIE 1978). Zyxwv99 (talk) 13:19, 15 June 2013 (UTC)

Agree. WP:SOFIXIT. SBHarris 18:48, 15 June 2013 (UTC)

Opening paragraph

The opening paragraph needs more descriptive information. Please take a look at the intro to the LED article, which has a lot more info.--Wyn.junior (talk) 13:16, 11 January 2014 (UTC)

Uses section

The Uses section of this article needs work. It needs headings or some bold for the individual uses. Someone should be able to skim the article and know what the uses are without actually reading it.--Wyn.junior (talk) 13:43, 11 January 2014 (UTC)

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Lengthy Theory of Concept

The section's a bit dense and contains too many different aspects of the functioning of a Laser diode. Also As detail and attention is given to a double-hetero structure laser diode, it seems that the fact a mono(or homo) structure laser is also just as significant, not necessarily in use, but as principle of operation. Thoughts?

I propose breaking up the section at least into two parts, one where the lasing of a laser diode is given detail, and then the principle behind the pumping process.

Ivangiesen (talk) 17:05, 14 February 2019 (UTC)

Lasing within Heterostructure

How exactly is the beam generated within a hetero-structure laser diode reflected off certain layers. I think a visual would elucidate the principle on which this works. Something to do with a varying refraction index values for each layer. Not sure on the specifics, but maybe this will jumpstart someone with more knowledge than myself.

Ivangiesen (talk) 17:18, 14 February 2019 (UTC)

The advantage of using a double hetero structure is vaguely explained and I don't think takes account of all the significant differences. A double hetero structure can run continuously, as opposed to a simple monostructure diode. Why exactly? I think something to do with the fact that less heat is generated to produce a beam of equivalent value, because somehow less volume is used. Again, not an expert, but find the explanation somewhat lacking, besides being simply too short. — Preceding unsigned comment added by Ivangiesen (talk • contribs) 17:33, 14 February 2019 (UTC)