Project 405

Quest for a Violet Laser


Introduction

(06 Dec 2008)

Having completed my powerful red laser about two years ago, I decided that it was time to increase my laser collection and begin work on another laser. Now the red laser project was only possible due to the production of cheap DVD burner drives, from which I could extract the powerful laser diode. DVDs use a 650nm laser to read/write DVDs. In early 2006, a new high-definition format was finalized - the Blu-ray Disc (BD). Now the difference of BD from DVD or CD was that it uses a blue laser (actually violet) to read and write on this new optical storage disc. The first BD players started shipping in mid 2006, though it faced competition from HD-DVD (which also uses the same violet laser). BD eventually won (in Feb 2008), leaving it as the sole victor and ending the format war between BD and HD-DVD.

The part that is relevant to this project is the violet laser diode which is inside all BD drives. Up till the mid 1990s, the only way to get a blue or violet laser was to use large and expensive gas-lasers requiring large amounts of power and strong cooling systems. Hence blue/violet lasers were much sought after. Only recently did technology allowed the creation of small and relatively inexpensive blue/violet laser diodes. So obviously I had to get one! The only barrier stopping me was the cost.

The most logical place to find this violet laser would be in any BD player, and I discovered that the Sony Playstation 3 had such a drive. Back in 2007, it was still reasonably expensive to buy one such PS3 laser module online (roughly in the range of USD$80). So I waited. Now in the closing of 2008, I managed to strike a deal of a brand-new PS3 laser module sled (complete with optics, with model number KES400A) for a relatively low price of $50SGD (eqv. to about USD$33)*, marking the birth of this little project!

*After more searching, it appears that the price of the diodes has dropped considerably, and I might be acquiring more, and higher-rated diodes for a more powerful laser*

UPDATES (Jan 2009)

Shortly after building the simple driver circuit for my KES400A laser, an accident caused Catastrophic Optical Damage of the KES400A laser diode, rendering useless. Fortunately, I simultaneously discovered a source for extremely affordable PHR803T laser sleds. These sleds are used in the Microsoft X-Box, and similar to the PS3's BD reading capabilities, contain a violet diode (in this case, used to read HD-DVDs). Unlike the KES400A, whose violet diode is packaged in the same diode package as the red and IR laser diodes, the PHR803t contains 2 separate diodes - one red/IR, and one purely violet. The good news is while the KES400A violet diode is known to be pushed to 20mW-30mW output max, the PHR803t has been known to operate quite happily up to 100mW! Given the low price, I bought some of them. By New Year's Day 2009, they had arrived to my house. Perfect opportunity to revive Project 405, and an exciting way to begin the new year.

This page layout has thus been reformatted, with latest news and photographs below the introduction, followed by details and optical characteristics of violet laser diodes, the KES400A diode, and finally the PHR803t diode.

Contents

1. Introduction
2. Optical Characteristics
3. KES400A - Extraction of the Laser Diode
4. KES400A - Design of the Drive Circuit
5. PHR803T - Extraction of the Laser Diode
6. PHR803T - Improved Design of the Drive Circuit
7. Construction of the Laser Enclosure
8. Project Results and Photographs
9. Good Links


Optical Characteristics

KES400A

I was unable to find the exact datasheet for the laser diode in the Sony PS3 laser assembly KES400A, but a quick search turned up some useful results. Laser diodes are not only extremely ESD (electrostatic discharge) sensitive, they are also very current sensitive and have a small working window for current. Too little current (below threshold) would not start lasing, but a bit too much would fry the laser diode. Due to lack of sensitive measuring equipment, I could not measure whatever current I was pumping into the diode. After some reading... I found out:

Violet Diode: manufactured by Nichia
Optical Output: 400-415nm, ~405nm
Threshold Current: 18-35mA (depending on batch)
Operating Voltage: 4.5-5.5V
Operating Current: ThresholdI+10mA to be safe
Typical Laser Output: =< 20mW
Temperature shift: +-0.04nm/degreeC
Operating Life-time: 5,000 - 10,000hrs at lowest operating current

To determine threshold current (if you have suitable equipment), hook up your laser diode to a controllable current source starting from 0mA and slowly turning it up. Even at low currents (as low as 1mA), some violet light can be seen. This is not lasing and should appear quite violet (in a diffuse circle) on a white piece of paper. Turning up the current slowly, observe the output and at threshold, the violet circle should turn into a dim blue oval (blue because the paper will fluoresce) with visible speckle. Record this threshold current. While the output (mW) increases generally linearly with the input current (mA), remember that driving it at higher power reduces the lifespan of the diode, and a bit too high results in a very expensive (and dim) LED, especially when Catastrophic Optical Damage (COD) occurs. When that occurs, optical output drops significantly at the same input power; beam symmetry would change, produce side lobes and spots, banding, etc..

Having had some experience driving the much more powerful 200mW red laser diode (previous project), and with the data gathered above, I was then able to proceed in creating a simple current regulating circuit to drive my violet laser.

PHR803T *New Jan 2009*

Similar to the diode in the Sony PS3 laser sled, the actual laser diode used in the X-Box PHR803T is unknown, and it is equally sensitive to ESD and current. However, the PHR803t has some very interesting characteristics which makes it more appealing than the KES400A. Of most significance is that it appears to be able to handle a much greater current, in the order of 100mA for stable operation, outputting ~80+mW at that power.

Like the KES400A diode, nobody really knows the exact part number for the diode itself, and hence nobody was able to find any datasheet. Fortunately, I managed to find some very useful charts from the good guys who took the effort to test (up to the point of failure!) and characterize the performance of this diode, by DrLava and Zom-B (in order of appearance):


Here Drlava has compared the PHR803t diode with the KES400A diode and one from a 6x BD writer


Zom-B writes along with his chart:
"The four of my 803T diodes performed quite differently. Heruursciences found a diode (Sharp GH04P21A2GE) which could be the diode in the 803T
because the specs are almost the same. Indeed, all my diodes fall within these specs. The horizontal and vertical colored lines were my
 recommended settings for each diode. The diode with the yellow line will probably go much higher, but I did not dare to do so at the moment, as it
was my most powerful specimen. Further analysis of the data (still in progress) reveals that even the diode with the blue line might go as high as 185mA."

After reading and considering, I thus came up with a general guideline with which to run these diodes safely and reliably (they can obviously handle much more power, but at a significantly reduced life-span.:

PHR803:
<125mA Maximum
<110mA Reasonable Lifespan in a Good diode
<100mA Maximum to be Safe
<95-97mA Ideal for long life-span
<80mA Safe

KES400A:
<50mA Maximum
<38mA Reasonable Lifespan in a Good diode
<20mA Safe (but might be below lasing threshold)

How bright should this laser look appear to our eyes?

You would probably have noticed that green laser pointers appear a lot brighter than their red counterparts; in fact, many companies latch on this fact to sell their lasers, claiming that their 5mW green laser is '20x brighter' than red lasers. But why do green 5mW lasers appear so much brighter than 5mW red lasers? It turns out that the human eye is more sensitive to the green wavelengths of light, much more so than violet or red. I found a nice chart listing the relative visibility of light at various wavelengths to the human eye at http://www.repairfaq.org/sam/laserioi.htm#ioicav2 and hence quote directly from the page:

The following table lists the relative sensitivity of the Mark-I eyeball to wavelengths (including common laser sources) of light throughout the visible spectrum and somewhat beyond. Of course, not everyone comes equally equipped. Your mileage may vary (and the number of significant figures in some of these entries should not be taken too seriously)!

Note: In the table below, the entry under 'Color' attempts to describe the actual appearance while the color listed under 'Typical Source/Application' is what you are likely to see in a laser catalog.

  Wavelength  Response   Color           Typical Source/Application
-------------------------------------------------------------------------------
    350 nm    .00001?  UV
    380 nm    .0002    Near UV
    400 nm    .0028    Border UV      Nichia violet GaN laser diode
    410 nm    .0074     "                  "
    420 nm    .0175    Violet
    442 nm    .0398    Violet-blue    Violet-blue line of HeCd laser
    450 nm    .0468    Blue
    457.5 nm  .0556     "             Blue frequency doubled Nd:YVO4
    457.9 nm  .0562     "             Blue line of argon ion laser
    473 nm    .104      "             Blue frequency doubled Nd:YAG
    488 nm    .191     Green-blue     Green-blue line of argon ion laser
    500 nm    .323     Blue-green
    510 nm    .503     Green          Emerald green line of copper vapor laser
    514.5 nm  .588      "             Green line of argon ion laser
    532 nm    .885      "             Green frequency doubled Nd:YAG or Nd:YVO4
    543.5 nm  .974      "             Green HeNe laser
    550 nm    .995     Yellow-green
    555 nm   1.000      "             Reference (peak) wavelength
    567 nm    .969      "             Green line of Helium-Mercury laser
    568 nm    .964      "             Y-G line of some krypton ion lasers
    578 nm    .889     Yellow         Gold line of copper vapor laser
    580 nm    .870      "
    594.1 nm  .706     Orange-yellow  Yellow HeNe laser
    600 nm    .631     Orange
    611.9 nm  .479     Red-orange     Orange HeNe laser
    615 nm    .441      "             Orange line of Helium-Mercury laser
    627 nm    .298      "             Orange line of Gold Vapor Laser
    632.8 nm  .237     Orange-red     Red HeNe laser
    635 nm    .217      "             Laser diode (DVD, newer laser pointers)
    640 nm    .175      "                 "
    645 nm    .138      "                 "
    647.1 nm  .125     Red            Red line of krypton or Ar/Kr ion laser
    650 nm    .107      "             Laser diode (DVD, newer laser pointers)
    655 nm    .082      "             Laser diode
    660 nm    .061      "                 "
    670 nm    .032      "             Laser diode (UPC scanners, old pointers)
    680 nm    .017      "
    685 nm    .0119    Deep red
    690 nm    .0082     "
    694.3 nm  .006      "             Ruby laser
    700 nm    .0041    Border IR
    750 nm    .00012   Near IR
    780 nm    .000015   "             CD player/CDROM/LaserDisc laser diode
    800 nm    3.7*10-6   "             Laser diodes for pumping Nd:YAG, Nd:YVO4
    850 nm    1.1*10-7   "
    900 nm    3.2*10-9   "
  1,064 nm    3*10-14    "             Nd lasers (including YAG)
  1,523.1 nm  0.0000    "             IR HeNe laser
  3,390 nm    0.0000   Mid-IR         IR HeNe laser
 10,600 nm    0.0000   Far-IR         CO2 laser

This is according to the 1988 C.I.E. Photopic Luminous Efficiency Function. A plot of these data may be found in Response of Human Eye Versus Wavelength. The C.I.E. (Committee Internationale d'Eclairage) may also be known by other initials indicating the English translation (ICI for "International Commission on Illumination").

A variety of information on color perception including many charts, tables, references, and links, can be found at the Color and Vision Research Laboratories of the University of California, San Diego. However, the corresponding table at this site is the older 1931 version. In 1988 C.I.E. updated the Photopic Luminous Efficiency Function because the 1931 function did not sufficiently weight the higher blue response of young people.

Notice that 555nm is the reference wavelength of maximum human response. Hence a red laser of 650nm at 0.107 would appear 8.3x less bright than a 532nm green laser of similar power, and my 405nm laser would appear some 87x less bright (using an extrapolated response figure) than an equivalent green laser!

But the violet Laser doesn't really seem that dim..?

If one has played around with such a (violet) laser, one would have noticed that (1) You can see the beam in the dark and (2) The laser spot looks bright for its wavelength. Why? The reason why such a [relatively] low powered violet laser produces a visible beam is due to Rayleigh Scattering, where the air molecules scatter the violet beam around (same reason why the sky is blue). In fact, you'd notice that violet beams have a characteristic 'misty' beam appearance due to precisely this reason.

Secondly, the laser really is quite dim especially when viewed on a non-fluorescing surface. But it turns out that many things around are fluorescent, e.g. paper or a white shirt washed with some detergents, which fluoresces blue, or in the case of the white paint on my home wall, white! In fact, you would notice that blue light (of roughly 450nm) appears approximately 9x brighter! If one were to shine the violet laser at a non-reflecting, non-fluorescent surface, you'd notice that it actually appears quite dim. These properties, coupled with the fact that many camera CCDs are more sensitive to violet than our eyes, would make for some good photographs! Now where do I find Uranium marbles...

(08 Dec 2008)

 

KES-400A

KES400A - Extraction of the Laser Diode

Here is a photograph of the actual laser diode assembly, part number KES 400A; laser diode assembly from a Sony PlayStation 3, size compared to a AA battery. The rubber mat surface is has 1cm grids..

After a quick inspection, it is immediately clear where the violet laser diode is (white arrow). The actual laser diode can actually contacts 3 different laser diodes - a 780nm IR, a 650nm red laser and the 405nm violet laser we're interested in. They are connected together inside a Common Cathode Can configuration, along with a photodiode.

Above shows the pinout of this laser diode, which doesn't seem so weird now that we have established that each different pin corresponds to a different diode. The case of the diode is also connected to ground.

To remove the diode, I first unscrewed two little screws holding the laser diode assembly in place. But the assembly still seems stuck to the rest because it is connected via a small ribbon cable to power it. I used a sharp knife to cut it and the laser diode assembly comes off after a bit of shaking.

The laser diode is still stuck on it's own little metal bracket, which holds it in place and also acts as a little bit of a heat-sink. But we can't use it yet unless we carefully extract it from it's housing.

In order to remove the diode from it's bracket, I scrapped off a bit of the thermal paste surrounding it and balanced it between two coins. If you look carefully at the front of the assembly, there are two slots beside the diode can. Using a small screw-driver, I carefully knocked it and got the diode out.

Here is the actual laser diode can, complete with the little bit of PCB and the ribbon cable which we have to remove. Extraction of laser diode - successful!

(7th Dec 2008)

 

Driver Circuit

Design of the Drive Circuit

Referring to the data gathered above 'Operating Life-time: 5,000 - 10,000hrs at lowest operating current', it is recommended that driving current should be =< +10mA of the threshold current. You can easily power the laser using a 9V battery (or 4-6 AA/AAA batteries) using a resistor to limit current. But given the sensitivity of the laser diode, I decided to use a simple LM317 current limiting circuit instead. See the links below for a better circuit (especially if you plan to use a 9VDC non-battery source to power the diode). Here is the circuit I designed for the laser:

I'm using the common LM317 regulator as a current regulator, in a TO220 package. After some random experimentation, I found an adjusting resistance of 32.4 Ohms to be a good value, limiting the current to 38.6mA. This adjustment is done using a 15Ohm resistor with a 100Ohm variable resistor. Any higher and I risk damaging the diode; any lower and the output becomes quite dim. I had initally planned to use rechargeable 1.2V NiMHs as the power source, hence I used a 6-battery battery holder (since the diode requires 4.5-5.5V for operation). Alternatively, a 9V battery can be used, at the expense of a shorter battery lifetime (but much more compact). Below shows the initial setup using 6 AA batteries.

Before soldering the circuit together, the components were assembled on a breadboard and tested. The resistance of the 100Ohm variable resistance was carefully tuned to ensure that I didn't overdrive and fry the laser diode. In the above photograph, the laser diode has already been assembled inside its casing. Read the following section for more details about the laser casing. Once I was sure that everyone was done (it is a rather simple circuit anyway) correctly, I hooked up the laser and was greeting with a lovely violet laser beam! Excellent.

For photographs of the KES400A product (and beam shots), scroll down to the results section. :)

Project Failure - COD of KES 400A Laser Diode

After a bit more effort, it was decided that the driver circuit be improve for more stable operation of the laser. This was done by adding a capacitor and diode in parallel to the laser diode, where the capacitor would soak up any voltage spikes from the battery (unlikely but possible), and the diode would sink any reverse voltage. To cut the story short, the diode failed to work after an initial positive attempt with the new driver. While the exact cause was indeterminate, the most likely cause was probably the capacitor shorting across the diode and thus frying it in the process. My KES400A diode was now rendered nothing more than an ELED (expensive LED). Like I said, I have no idea what exactly caused it but it led me to formulate the following precautions for my future laser work:

- Complete the entire driver assembly, solder it properly together, and doublecheck components and wiring before attaching diode
- Handle diodes with a lot of care (protection from ESD)
- When in doubt, do not try. Find out first!
- Install a switch to the circuit (vs. touching leads to diode)

Reality

No. of violet diodes now = 0
Therefore, I am unable to continue my project. Unless I get some new diodes.... (Dec 2008)

Update- Jan 2009 - New set of PHR803t violet diodes have arrived! (Continue reading below!)

 

PHR803T Laser Diode

PHR803t - Extraction of the Laser Diode

So just around New Year's Day 2009, I received my package of 3 PHR803t laser diode sleds (group buy) from the X-Box (as mentioned above), along with another sled from a 20x DVD burner (for a subsequent project). There you see the laser sled and part number sticker.

First up was to remove the metal bracket covering the diodes. This is easily done by unscrewing it. You should be able to see two separate diodes; one with 3 pins and another with 4. The one with 4 is the IR/Red diode and the one with 3 is the nice violet diode, which is the one we're interested in! By then I had completed my driver (see below for driver details) and did a quick test to determine if it was indeed the right sled. A flash of lovely violet spilled out all over my desktop! Note the little vial of sodium fluorescein.

Close up of the diode with labeled pinouts. Notice that it's seated in it's own little metal heat-sink, which is in turn glued onto the main assembly.

Extraction was easy; the first step was to chip away the glue holding the diode bracket to the main assembly. Once that was out, a little twist using two pliers easily snapped the diode bracket into to and allowed for easy removal of the diode. I decided not to remove the little PCB attached to the diode to avoid risking burning it out with my soldering iron. Like the KES400A, the next step was then to hammer it into the Aixiz housing (using a small screwdriver and a small hammer), then carefully soldering output wires from the diode. Extraction completed successfully!

(24 Jan 2009)

PHR803T Laser Driver Circuit

After a bit of tinkering, I settled for a improved driver circuit. It's essentially the same as the previous one, except for the inclusion of 3 additional components. The LM317 provides the current regulation. Power output is set to 1.24/13.1Ohm = ~95.4mA to the PHR803t diode. The 47uF 25V tantalum capacitor absorbs any residual battery voltage spikes; the 1.2k resistor drains away the capacitor charge when power is turned off, and the 1N4002 diode protects the laser diode from back currents. The circuit is powered by a single 9V battery. Of course the 1.2k resistor eats some current away (~3mA) so the total power to the diode is just over 90mA. This should give me around 60 - 90mW output of consistent and reliable laser light.

After testing out the circuit on a breadboard, the components were carefully soldered together as a single complete package without the need for a PCB. Design and construction took half an afternoon on the 3rd Jan 2009.


Construction of the Laser Enclosure

Laser and Collimator assembly

Due to the characteristics of the laser diode's emitting junction, the emitted laser beam is wedge-shaped and very divergent. In fact, divergence of the X and Y beams are unequal and the focal lengths required to collimate the beam differs slightly. The general emitted beam shape will appear elliptical/asymmetric, and generally linearly polarized. In any case, given a beam divergence of 10 to 30 degrees from the laser diode can, external optics are required to collimate it. In order to save the trouble of finding a suitable lens and enclosure, I purchased a 650nm 12x30mm + case for $4.50USD from Aixiz Lasers (http://mfgcn.com/_wsn/page2.html). Perfect for my purpose and not overly expensive either.

Above are the original 650nm red laser diodes. (Referring to the second photo), the right most laser being the 10mW one and the left most the 5mw one. Notice the difference in beam output (they're both under-driven though). Nonetheless, I had to sacrifice the red laser diode to make way for the new violet diode!

The first step was to open up the diode casing, both the back assembly as well as the front lens assembly. Once this was done, I now had to find a way to remove the red diode which was attached firmly to the casing (see last photograph, where the diode is in the centre). The most obvious way would be to hammer the diode out using a nail-like object, but I tried a more subtle approach and...

Managed to pry out the red diode without damage to the diode AND the casing! Note the small driver circuit attached to the red laser diode. Yes it still works perfectly fine and well! Brilliant!

Remember the raw violet diode? I still had to remove the PCB and with 5 very fragile pins attached to it, it was quite a daunting task to remove. I eventually did but almost destroyed the whole diode. Maybe those of you with better soldering skills can do a better job. Nonetheless, I fired up the diode and it worked perfectly fine. Hammered it carefully into the casing (which also acts as a good heat-sink), soldered two wires to it, and assembled the whole thing back to how it should be. :) The process was exactly the same as for the PHR803t diode (right photograph), though I chose not to remove the PCB to avoid damaging the entire diode. (3 Jan 2009)

(12 Dec 2008)

Entire Laser Enclosure (for PHR803t)

Back in 2006, I constructed my red laser enclosure completely out of clear acrylic. Unable to find a more appropriate host, I resorted to the same tried and tested acrylic method and built a completely new enclosure for the violet laser. This took a complete afternoon of 3rd Jan 2009 (including design and assembly of the driver).

Note the overall design compared with the red laser. It's more compact and more sturdy, and does with it's supposed to do well. Features include: One momentary push button, one pole switch, and a stainless-steel wire battery catch. :) Violet Laser Complete!


Project Results and Photographs

Initial Results with KES400A laser diode

Immediately after assembling the KES400A laser into the collimator, I tested it out with some excellent results.

Here is the laser aimed at two glass vials containing a Quinine solution and a Sodium Fluorescein solution. Quinine has two main excitation wavelengths of ~250 and 350nm, with an emission wavelength of aqua blue 450nm; Fluorescein has an absorption maximum at 494nm and a strong emission of green 521nm in water. The quinine solution is none other than 'Tonic Water', available at all supermarkets and also commonly sold as 'bitter lemon'. Read here for more information. The violet laser doesn't appear that bright nor bluish as seen in the photograph though. In reality, it's a much deeper purple, more similar to commercial black-lights.

A nicer photograph with background lighting. Notice the driving circuit behind the laser, which is sitting atop a stapler box. Unfortunately, you cannot 'see' the beam since this laser is quite low powered. The photographs were taken with a bit of smoke created using a burning match. More photographs to come!

(12 Dec 2008)

 

Further Results with KES400A Laser Diode

Unfortunately I do not have a fog machine to make nice beams, nor do I have much optical accessories like mirrors or prisms, so we'll just make do with the above laser playground for now. It's just a clear box containing fluorescent water (water with some highlighter ink dipped in), some aluminium foil as 'mirrors' and one glass semi-circle block (which is about the only optical accessory I have). Laser is shining from the bottom right. Enjoy! I do not have any equipment to measure the output of the laser at the moment.

 

NEW - Results of PHR803T Laser Diode

Initial results of both the red and violet laser in action.

A Better and more realistic photograph of both lasers in action. The output of the violet laser is visible cleaner (much less speckle). While the violet laser itself is not very powerful, it appears extremely bright especially on white paper (which fluoresces a very bright blue), and outshines even the more powerful red laser. More photographs to come!

(04 Jan 2009)

... to be continued...

 

Good Links

The cool thing about the internet is its connectivity - manifesting itself in the form of hyperlinks! Here are some nice and very useful webpages which helped me in Project 405.

http://www.wickedlasers.com - Very nice website selling very powerful lasers; visit their forum for nice discussions on lasers
http://www.repairfaq.org/sam/Blu-ray/site1/index.html - Dissection of a BluRay Reader Assembly; very useful webpage from which I learned a lot from
http://www.repairfaq.org/sam/laserfaq.htm - Sam's Laser FAQ; THE definitive source for all lasers! A must read for any laser enthusiast
http://www.wikipedia.com - Just read it for great general knowledge :)


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(c) Gao Guangyan 2008, 2009 Projects
Contact: loneoceans [at] gmail [dot] com 

 

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