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Violet BluRay / HD DVD laser

   To increase density of data storage in optical discs, a shorter wavelength of the light is needed. This is why Blu-Ray and HD DVD drives uses 405nm laser diodes (for DVD it's 650nm and for CD it's 780nm). Radiation with wavelength of 405nm is a visible light in violet color. The most popular devices that has this type of laser diode inside are drives designed for PCs or notebooks, Play Station 3 consoles (Blu-Ray readers) and external HD DVD readers for Xbox360 consoles. Lasers described here comes from PS3 console and Xbox HD DVD readers. Below you can see two long pictures that shows step by step how to get out the laser diode. On the left is a Play Station 3 and on the right is an Xbox360 HD drive.

                               

   That drives can also read CD and DVD discs so there are actually three laser diodes in both of them. In PS3 all three diodes are closed in one 5-pin casing, while in Xbox drive 650nm and 780nm diodes are closed in one 4-pin casing, but 405nm diode has a separate casing (standard 3-pin). All of that diodes are in TO-18 casings.

   In Xbox HD DVD drives two different kinds of the laser sleds can be found. They are labeled DT0811 and PHR-803T, the second one is older and rare, a laser diode in it has greater power than in DT0811. On two pictures below both kinds of sleds are shown.

   All of the diodes I've taken out from DT0811 sleds had their maximum current less than 130mA, mostly it was about 100mA. Above that current some areas of the diode structure stops lasing (temporary) - it means that the diode is just about to die. I've found only two PHR-803T sleds in several drives that I've had, one of that diodes works fine at 300mA (I haven't tried more), but the other one died when I tried to power it from 250mA (or it has been already dead because of ESD or something, but I doubt it). According to other laser freaks's power measures, the optical power of these diodes is equal by value to the current flowing through the diode. It means that this laser diode powered by 100ma of current can emit even 100mW of light. At this current and collimation with an acrylic lens that diodes can light matches, so this power is quite possible. Below you can watch a video with laser diode from DT0811 at 105mA lighting matches.

   Voltage drop of these diodes is 5-6V depending on current. It's quite much in compare to DVD laser diodes (about 3V) or IR laser diodes (2-2.5V) - light emission at such a short wavelength needs greater barrier voltage in semiconductor because photon energy @405nm is a bit more than 3eV.

   PS3 diode's power is the least, because it's max current is about 50mA. Light at 405nm is seen by human eye as violet. It's poorly visible, eye sensitivity at this wavelength is about 200 times less than at 555nm (green) and 20 times less than at 650nm. Below you can see a V(λ) chart showing dependence between eye sensitivity and wavelength. I've marked some kinds of lasers on this chart.

   It's hard to show this color on photos, because digital camera sees this light as a blue (every pixel of a CCD sensor is made of red, green and blue sensors and only the blue sensor responds to the 405nm light). On the left picture below you can see a PS3 diode in comparison with Xbox HD drive diode at the same current 50mA (diodes are connected in series) - there's no visible differences. The PCB that is shown on that picture is a dual regulated current source that I've built specially for powering laser diodes, it's described HERE. On the right picture is a light beam from DT0811 diode, it's clearly visible at night even in clean air.

   Light from these lasers looks like bright blue when falling on a white sheet of paper. It's because of a bleach used in paper manufacture that fluorizes blue under UV light. The wavelength of the light emited by described laser diodes is short enough to cause that bleach to fluorize. Some of the 405nm light is absorbed and then the bleach emits a longer wavelength light, that is better seen by human eye so it looks brighter.
   The right picture below shows some 405nm laser modules and a 650nm module with a DVD-RW diode (@250mA). I used a tiny buck driver to power each diode - this circuit is described HERE.

   Below two macro pics of the DT0811 laser diode structure.

   The left one has been taken through a red glass, so that all the high power violet light that is dangerous for the camera was stopped. A thin wire that supplies current for the diode is clearly visible. The right pic shows the same laser diode but it has been taken through a glass from a welding mask. That glass attenuates all of the light very strongly. On this picture you can see that LASER effect acts only on a tiny spot in the corner of the crystal actually.

   Here some pictures of a laser module with a DT0811 laser diode with a red (DVD-RW) and green (5mW DPSS pointer) lasers. There's also a violet pointer that I've made. Unfortunately the case I've used for it is pink, but I haven't had another one! so please don't laugh :P There's a 9V battery inside and a little driver I mentioned before.

   

   

   The next three pictures shows that three laser spots merged on a sheet of paper.

   

   With that three lasers, 650, 532 and 405nm it's possible to make an 'quasi RGB' laser. Quasi, because the last one is actually violet, not blue. Appropriate dichroic filters can be used for combining that three different color beams. Then you need only (or as much as :P) a pair of galvo scanners to make a 'qRGB' laser projector or a laser show system! Recently I've had an occasion to buy that kind of scanners with an amp really cheap. I didn't know if it works properly but I managed with putting it all together and now it works fine, bit details of this will wait for another article on this website :) Now I will show you only two pics and one video showing these galvos with a PHR-803T laser diode module. The patterns are bright blue, not violet, because I used a white sheet of paper as a screen.



   405nm light is almost an ultraviolet, so the laser beam is visible in water with some highlighter marker dye diluted in it. A 'glow in dark' paint also reacts on that light, so it's possible to write i.e. on evacuation signs with 405nm laser pointer.

   There's some water solution of a radiator liquid in a couvett on the left picture. It turned out that this liquid fluorizes green really nice under 405nm light. The light beam is guided into the liquid at angle that is less than the critical angle so the light is reflected between the liquid surfaces. That's exactly how a multimode fibers work. On the right pic you can see a ghost that was painted with a glowing in dark paint, and a glowing curve on it made with my violet laser pointer.

   Here are links to two web pages with descriptions of similar lasers:

  • http://www.fineartradiography.com/hobbies/lasers/blu-ray/
  • http://ledmuseum.candlepower.us/eighth/blu-ray.htm

       ADDED, 2.09.2009

       As it was not hard to guess, 405nm laser pointers appeard on ebay recently. Of course I had to buy a few of them to see how they looks like :D

       Below you can see some pictures of these pointers. The casing is the same as in cheap chinese green laser pointers. These 405nm pointers obviously are chinese too :P

       The optics in not so sophisticated, because this is regular diode laser, not a DPSS laser like green pointers. But the laser diode driver is something interesting. The pointer is powered from two AAA cells, so it's 3V. Voltage drop across 405nm diode is about 5V. That's why the driver has a BOOST converter on board for increasing voltage to that level. Unfortunately, I didn't manage to take the driver out without damaging the pointer casing, so I won't show how the driver looks like here because I don't want to destroy any of these pointers.

       The optical power, according to the safety sticker, is lower than 5mW. But on the other hand, that value was printed on a piece of sticker hiding '<10mW' value, what you cen see on pictures below :P I'm not sure what was going on here but it's funny :P At last, the third picture shows what my laser power meter says about this pointer. The measure result is a bit over 40mW ...

       And here are a few nice photos with smoke and comparison of one of described 405nm pointers with a 50mW green and a 100mW red pointer.

       

       ADDED, 31.01.2010

       A few days ago, when taking out another 405nm laser diode from PHR-803T laser sled I decided to take the sled totally apart for fun and to see what's actually there. First of the pictures shown below shows all elements I found in the sled and a short description of that stuff.

       I think that the most interesting elements are diffraction gratings (10 and 11) and a small LCD panel (3). The gratings are used to generate additional beams of light than the main beam (which becomes a 'zero order' beam after passing the grating). That additional beams helps the focusing system to focus the light on the disc surface (something like AF assist in still cameras). It's quite untypical application for diffraction gratings because they're mostly used for splitting light for it's spectral components. This system can be also found in DVD drives, but not in all of them. I got the gratings' d numbers (which is equal to space between slits) by simply pointing a laser pointer with known wavelength on the grating, measuring distance from the grating to a screen (a wall, in this case) and distance between zero and first order dots and doing some simple calculations.

       The liquid crystal panel (actually it's not an LCD because it's not a display) is much more mysterious element. Something like this can be found also in laser sled from PS3 console (BluRay reader), so in laser modules that works with 405nm light, but there's no such things in DVD or CD lasers. After a few minutes of googling I found two websites giving some information about this element (here and here). There's no polarizers on the panel surfaces like in LCD displays, so it doesn't change the wave's amplitude but only changes it's phase. It's kind of tunable optical retarder divided for several areas controlled separately. It's used to correct wavefront aberration, whis is simply equalizing wave phase in beam's cross section. Probably it has to be done because of relatively wide band of this optic system (from 405nm for HD DVD and BluRay to 780nm for CD). Three of the pictures shown below presents this LC panel. After putting it between two crossed linear light polarizers (one of them was that one built-in into my notebook's screen ;) ) it behaves like an LCD so cells becomes visible. Notice that tiny IC that is mounted on the connecting tape :)

       The other pretty nice macro pictures shows the 405nm laser diode. I didn't use any microscope or sophisticated equipment to take these pics, just my favourite PowerShot A700 compact camera without any converters :)








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