Nowadays you can find lots of cheap laser diodes emitting light at wavelengths such as 405, 450, ~640, ≥780 and, since recently, also ~520 nm. But it's really hard to find a laser diode emitting at 590 nm or around that (if they even exist yet). It's moderately easy to find (very expensive) DPSS lasers with sum-frequency generation—but not a diode one.

At the same time it's very easy to find orange LEDs. They have been around for decades: I had a cell phone with orange backlight about 20 years ago. So apparently, making p-n junctions in semiconductors with the necessary band gap has long been possible.

What is then the reason that orange diode lasers are still not common (or don't exist)?

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    \$\begingroup\$ Orange LEDs using AlGaInP for 590–620nm visible light. However AlGaInP lasers emit in 630-760 range, which is red and infrared. I have no idea about the physical aspect of this, only saying that you cannot draw parallels between LEDs and laser diodes. \$\endgroup\$
    – Maple
    Dec 8 '19 at 16:41
  • \$\begingroup\$ This isn't an answer because it's supposition: I suspect that there's not much market pressure for an orange laser. You want lasers that work at all or that propagate in fibers for communications -- hence IR. You want lasers with as short of wavelength as you can get -- hence red, and then the jump to blue. But once you've got cheap red lasers, and effective blue or ultraviolet lasers, why go backward to orange? \$\endgroup\$
    – TimWescott
    Dec 8 '19 at 17:31
  • \$\begingroup\$ @TimWescott well, they did go back to deep green (510-520 nm), as well as cyan (490 nm). All these are easy to find at ebay or aliexpress. So, why not something between green and red? There are also some medical applications of yellow and orange lasers. \$\endgroup\$
    – Ruslan
    Dec 8 '19 at 17:58
  • \$\begingroup\$ @ruslan Semiconductor materials don't work like that. If you don't have the materials to do it, you can't do it. You can't just mix a little red and a little green and get something in between. These aren't paints. \$\endgroup\$
    – DKNguyen
    Dec 8 '19 at 19:53
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    \$\begingroup\$ @KevinWhite it's the DPSS that you describe (532 nm=1064 nm/2). A little while ago pure diode ones appeared, emitting 510-520 nm. \$\endgroup\$
    – Ruslan
    Dec 9 '19 at 5:08

LEDs and lasers are different types of a devices. The light emitting medium in a laser has to be capable of population inversion, where more emitters are in the excited state that in the ground state. This requires complex 3 or 4 level systems with long lifetime intermediate states. Once the population is inverted you get light amplification through stimulated emission - lasing.

An LED just has to emit light, so lots of materials that can be used to make good LEDs cannot be used for laser gain media. I don't know the detailed energy levels of orange LEDs, but probably they are not suitable for laser gain media.

Edit: Based on the other comments, it is worth pointing out that good laser gain media are rare. Most materials, even those that efficiently emit light, cannot efficiently amplify it and so make bad lasers. Of those that make good lasers, those that can be electrically pumped are even rarer. That is why high power laser diodes are available at just a handful of wavelengths; there happens to be an exceptional material available for that specific photon energy.


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