Project 405
The 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)
==================================== KES400A
====================================
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)
KES400A - 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
====================================
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 - Improved Design of the Drive 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/Videos
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 :)
Back to
main page
(c) Gao Guangyan
2008, 2009
Projects
Contact: loneoceans [at] gmail [dot] com
