About

This is a blog related to my laser web site. I get lots of questions by email and I thought a blog would be more suitable for discussions, see let’s see how it works! Please feel free to drop by, english and german spoken here.

Contact me under: rxlaser #at# k-net.fr

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34 Responses to “About”

  1. Richard Schatz Says:

    Hi,

    We really share the same interests. I started with radio in the seventies, building transmitters and receivers for shortwave and FM-band. Since 1987 I have been a researcher in photonics at Royal Institute of Technology designing single mode lasers for telecommunications (1.55µm). I am very impressed by your work with the lasers and laser drivers and the holograms you have made. I wonder if you have the remaining 60 mW 658 nm mode laser still for sale? I am interested to buy it.

  2. rxlaser Says:

    Hi Richard,

    thanks for your interest! Well right now I am having returns due to lasers not running clean single mode, one laser came back with a completely distorted spectrum. I need to find out what had happened and so far I’ll put everything on hold!

    Best regards,
    W

    • Barrie Monkman Says:

      Hi,

      I have been trying to send you an email but it gets blocked.
      Here it is posted on your blog.I can understand you must get inundated with emails, so if this gets boring for you go to the end two paragraphs where I get to the crux of my question.
      I have read some of your Laser- Projects page, especially the parts relating to holography. You certainly know your stuff, I can follow about a third of what you
      discuss and then the rest goes over my head. I became an electrician in my younger years but gave it up about 40 years ago for professional diving.
      If I had the time I would study in more detail the properties of lasers and diodes which would give me a greater understanding of the complexity and behavior of light waves.
      When you mention that differences in temperature of just 1/1000 of a degree can alter the stability of a diode, plus understanding the driver circuitry to keep the diode
      as stable as possible at the lasing threshold, leaves me wondering at my age whether I would have the time to take on the challenges to use diodes to follow my desire
      to make color holograms.

      About 20 years ago after reading a book I was lucky enough to make some 4”x 5” reflection holograms using a Red 640nm infiniter 4mw laser pointer on the old Russian “ Red Star”
      holographic film ( I have still kept about 30 sheets of film in the refrigerator all this time but I imagine its useless by now). To my surprise the exposures came out clean with no noise or grain. At the time the infiniter pointers were supposedly considered to be among the best of the low wattage diodes with good coherence length and a stable beam( I don’t know if you have looked at these in times past ?). Whether it was the beam quality or the fact I had extremely stable conditions. I set up a basic table on inner tubes down an opal mine, well out in the desert area. This opal field is called “Lightning Ridge” It is so quiet you could hear the silence. The mines temperature would have been very consistent with zero airflow. Perhaps this contributed to how well the holograms came out. Rainbow holograms were being made at the time but I didn’t keep in touch with it all, life’s pattern taking a different path.

      That is until recently I have seen some amazing full color holograms done by Hans Bjelkhausen, Yves Gentet and others. (I notice an excellent hologram of your shell is on the Gentet website using his high resolution emulsions). Seeing these has renewed my passion in holography immensely. I can’t see myself producing holograms of this quality, I imagine there is so much to learn, but I would like to try.
      This is why I wouldn’t have the time or the electronic equipment to build driver circuitry and build lasers. I have basic electrical monitoring equipment but no oscilloscopes etc. I have a workshop where I can weld and turn down parts that would be needed to build a good table and instrument supports. But I have no light source at the moment ! Except for the infiniter pointer.

      Which brings me to my questions and I hope you can offer me some advice.
      I see you are not selling any of your laser equipment for reasons I can understand.
      Hans Bjelkhausen has suggested to me I can but a Green laser: 532 nm at output power 100 mW (Cobolt Samba DPSS laser);
      and a Blue laser: 457 nm at output power 50 mW (Colbolt Twist DPSS laser).
      I am waiting for Cobolt to get back to me. These solid state lasers sound like they are among the best but I know the price they will quote will terrify me !!
      Whats in that little box ? Is it a special diode? The crystal or the solid state Circuitry? ( or all of the above)
      I have a resonable budget but I don’t want to go in to the tens of thousands of dollars for a set of RGB lasers.
      You have done a study on the Coherent compass 315-M 532 nm which you calculate is excellent for holography. I can pick a good one of these up for around $1800.
      This will put me in the middle of the green but I will still need a red and the elusive blue. I read about the blue 457 nm nichia diode you studied which would be nice for a handful of dollars if it could be made stable. Litiholo have a blue and green diode in a kit, no disrespect to them but I think they must be low milliwatt for school students, its shot on polymer and the images appear to be very grainy and low quality.
      Bottom line is with all your expertise and my lack of it, what is your opinion which are the best (RGB) lasers or DPSS lasers that are trouble free for holography use, and are best value for money?

      Oh finally the DPSS laser modules have a cooling fan as well as a heat sink.
      Do you turn the fan off just before you shoot? I imagine that any kind of movement on the table will vibe out the exposure.

      I hope you can shed some insight and point me in the right direction, I will appreciate your help.

      Thank you in advance.
      Best regards

      Barrie

      • rxlaser Says:

        Hi Barrie,

        glad you found it interesting!

        Here are few comments:

        1) Laser pointers use low power diodes, like 1mW, and many if not most diodes run single mode there. The tricky point is to boost this beyond 10 or 20mW.

        2) The DPSS Lasers you mention use crystals that are pumped by infrared laser diodes, typically in the Watt range. They involve a number of high precision optics and often complicated resonators, and that’s why the single mode versions of such lasers are as excessively expensive as stable. The Coherent Compass’ are excellent!
        Some variants are a bit different like the Coherent Sapphire at 488nm. Sometimes one can get good used ones eg on ebay but they are usually retired near the end of lifetime with often reduced specs. So it’s a gamble.

        3) As for recommendations: For green there are are plenty of possibilities in the form of single mode DPSS lasers. That’s the least of the problem. For red, medium power laser diodes can work fine at 50-100mW. They are not too difficult to be built of one keeps power low. A HeNe is the least cumbersome laser, though.

        The problem is for blue. Despite it is possible to get 100mW blue out from laser diodes, these things tend to be orders of magnitude less stable. Blue Coherent Sapphire lasers might be a way to go, but typically they have 488nm which is not ideal. I got one of those which is good at 15-20mW, I am however undecided whether I like to sell it.

        4) I am still trying to construct a stable blue ECDL laser with Osram diodes, but above 20mW or so they become really unstable. So far I dont have a satisfactory solution, partly because I took a break for a couple of years due to job workload. But recently I was restarting work on diode amd TEC drivers. I am more into electronics than holography, I confess 😉

        5) Yes, a fan is something that should not be running openly in the vicinity of a holography setup, even the slightest air drafts can ruin a hologram. Switching off just before the hologram shot can make the laser mode jump, I think it is best to shield the laser thermally off but keep it running.

        6) There are varius websites, sometimes ppl sell lasers there, eg at
        http://www.photonlexicon.com/forums/forumdisplay.php/54-Hologeekery
        There is also a FB holography group.

        I hope that helped!

        Regards,
        W.

  3. Richard Schatz Says:

    Hi,

    Well, single mode stability at high power is very tricky. Even change of humidity in the air can change the AR-coatings, giving weak back reflections distorting the spectrum. And at high power spatial hole burning can cause DFB lasers to become multimode due to the induced chirp of the grating.

    Please let me know your progress. In fact, I am still interested to buy your complete laser package with current and TEC even without any single mode laser mounted because I expect cheap devices with better single mode performance on the market soon. Ondax seems to have good single mode lasers with external gratings throughout the visible wavelength range but the prices are still too high for me.

    You have an impressive lab including the the almost homebuilt OSA with parallell wavelength readout! Your experience would be invaluablein any university or R&D lab.

    Richard

  4. Guido Hoppe Says:

    Hallo W,

    ich bin auf der Suche nach einem Ersatz für meinen alten HeNe Laser.
    Der 640nm Laser hat mein Interesse geweckt. Wie ist das mit dem Strahlprofil, geht der sauber durch das Raumfilter, oder ist da noch eine aufwändigere Strahlformung notwendig?
    Gibt es schon Erfahrungen zur Lebenserwartung?
    Wäre ein Gerät verfügbar?

    Viele Grüße
    Guido

  5. rxlaser Says:

    Hi Guido,

    es haengt vom Collimator ab, je nachdem bekommt man einen duennen Strahl mit schlechterer Qualitaet aber 10-15% mehr Leistung, oder einen dickeren aber ganz sauberen Strahl mit eben etwas weniger Leitsung. Im Moment versuche ich einen Collimator zu finden, der guter Kompromiss ist.

    Ueber Lebenserwartung kann ich kaum etwsa sagen, ausser dass die Dioden typischerweise im Bereich von 50% ihrer Nennleistung betrieben werden (darueberhinaus wird single mode immer schwieriger) und bei reduzierter Temperatur, so dass von der Diode her eine sehr lange Lebensdauer erwartet werden kann,

    Ja, ich denke ich werde einen 640nm Laser in Kuerze zur Verfuegung haben, allerdings gibt es noch einen anderen Interessenten den ich zuerst fragen werde, weil er sich frueher gemeldet hat. Mittelfristig plane ich ein paar ECDL. zu bauen.

    Danke fuers Interesse,
    und vieke Gruesse,
    W.

  6. Guido Hoppe Says:

    Hallo W,

    noch habe ich etwas Zeit, der alte Laser läuft ja noch.
    Was würde die ECDL Version in etwa kosten?
    Um ein kreisrundes Strahlprofil zu erhalten, möchte ich gerne ein anamorphes Prismenpaar integrieren. Wäre das möglich?
    Optische Strahlengänge könnte mein Kollege mit OSLO simulieren.
    Um das Prismenparr nebst geeigneter Fassung würde ich mich gegebenen Falles kümmern.

    Viele Grüße
    Guido

  7. rxlaser Says:

    Hallo, also fuer das Gitter plus den feinverstellbaren mount waeren das schonmal 100$ mehr, in etwa. Die Frage ist nur, ob ein ECDL laser ueberhaupt besser funktionieren wuerde, bisher ist das nicht so klar (dh ob die single mode Leistung ueberhaupt entscheidend hoeher ist).

    Mit An. Prismenpaar integrieren… ist gemeint: in den Laserkopf? Also in die bisherigen passt das nicht mehr, aber in einen ECDL waere das nach Absprache wohl schon moeglich. An sich ist es eine gute Idee, nur sind eben solche Prismenpaare, wenn sie entspiegelt sind, recht teuer. Jedenfalls haben die 640nm Opnext dioden schon ein recht unsymmetrisches Strahlprofil, und zwar im Verhaeltnis zur Polarisation in eine unguenstige Richtung, also koennte sich das uu schon lohnen. Kennen Sie eine gute Quelle solche Prismen?
    Ich habe leider nur welche fuer 532nm.
    Viele Gruesse,
    W

  8. Guido Hoppe Says:

    Hallo W,

    70mW wären für mich schon ein Traum, aber ich hörte der ECDL sei weniger anfällig für Rückreflektionen, also evtl. stabiler im single Mode Betrieb, daher mein Interesse.
    Sie haben sicher noch mit dem Agfa Holotest Material Erfahrung gemacht,
    ich zehre immer noch von alten Beständen. Wie ist die Empfindlichkeit vom Ultimate 08 in Relation zu Holotest 8E75 (oder 8E56)?
    Ich habe bis gestern geglaubt das Prismenpaar muß direkt hinter die Diode, was aber bei den Divergenzwinkeln schon wenig Praktikabel wäre.
    Wenn das Gehäuse beim Strahlaustritt einige Gewindebohrungen hätte, um evtl. eine Strahlformung nachzurüsten, bräuchte mann nicht am fertig abgestimmten Gerät herum zu bohren.
    Eine gute Quelle für die Prismen? Bei Edmund S. gibt es zumindest welche, die brauchbar scheinen, kosten aber nackt ca 150€.
    Es gibt auch eine gefasste Version, aber die lässt sich wahrscheinlich schlecht anpassen und kostet knapp 400€ mit Mwst, da versuche ich lieber selbst eine Aufnahme zu konstruieren.

    Viele Grüße
    G. Hoppe

  9. rxlaser Says:

    Hallo,

    nein mit Agfa habe ich keine Erfahrungen, aber sehr gute mit beiden Ultimates – aber fast ausschliesslich nur bei 514nm.

    In Bezug auf Anamorphic Prisms.. ich habe etwas herumgeguckt, ja die von EO schauen gut aus, sind beschichtet, aber ob es der Preis wert ist…ich weis nicht. Jedenfalls wollte ich mal gelegentlich bei diversen chinesischen Firmen herumfragen, uu ware ein Gruppenkauf einer groesseren Anzahl lohnend.

    In Bezug auf Stabilitaet sind soweit ich sehe, ECDL nicht unbedingt besser, sie neigen viel leichter zu mode jumps, der Hauptunterschied ist m.E. die sehr geringe Linienbreite, was fuer uns aber nicht so relevant ist. Jedenfalls ist die Variabilitaet selbst zwischen Dioden gleichen Typs gross und ich habe bisher noch keine klare Linie sehen koennen.

    Viele Gruesse,
    W.

  10. Guido Hoppe Says:

    Hallo W,

    dann harre ich fortan geduldig in Erwartung eines verfügbaren 640nm Lasers von Ihnen.

    Viele Grüße
    Guido

  11. Wenhai Lee Says:

    Hello W,
    I am a teacher at University of Ottawa, and I am interested in your works on lasers. I’m wondering if you still have some 1MHz wide band low noise photodetector for sale? PCB or completed boards are ok. If so, please tell me the costs with quantity of 5. Thanks a lot.

    Wenhai

  12. Guido Hoppe Says:

    Hallo W,

    hat mit der HL6385 Diode schon einmal jemand erfolgreich Hologramme (auch split-beam) aufbelichtet!

    Viele Grüße
    Guido

  13. rxlaser Says:

    Hi Guido,

    ja ein sehr bekannter Holographer hat zwei meiner HL6385 Koepfe mittels Hologrammen getestet und sie danach gekauft, den Namen sende ich per mail.

    NB: ich habe wieder ein paar dieser Dioden aufgetrieben und moechte sie fuer ECDL verwenden. Leider haelt mich die Mechanik etwas auf.

    Viele Gruesse,
    W

  14. Leslie Says:

    Hi,

    I found your website via google when looking for a PWM TWC controller – specifically this page:
    http://redlum.xohp.pagesperso-orange.fr/electronics/PWM-TEC.html

    I ahe been getting into TEC cooling for PCs and was looking for a PWM TEC controller, but none seem to suit the application.

    As you are sure to know, CPU’s in PC’s put out a HUGE heatload, sometimes up near 300W, and to cool that heatload requires a number of TECs drawing a large current (sometimes upto 80A in some configurations) – but it has been impossible to find any PWM TEC controllers that would support such high current output.

    If it is not too much bother, would you have the time to let me know what would need to be modified with your PWM TEC controller for it to support at least 50A output current?

    Please let me know if this would be possible and if you would be able to do that and post a revised schematic.

    Much appreciated,
    Leslie

    • rxlaser Says:

      Hi Leslie,

      I am surprised that 50A or 80A were necessary. Most higher power TECs use like 10 or 15A but higher voltages, and if one needs more power one can put them in series so that only the voltage needs grow. The higher voltage of a few tens of volts is no big issue at all. Producing moderate currents like 10-15A is at least an order of magnitude easier than producing 50A or 80A; that would require very special cores for the inductors, capacitors, even the wiring, etc. I didn’t build such a thing but I would recommend not to attempt this without a lot of experience; doing 10A is already a challenge for the newcomer!

  15. Phil Bergeron Says:

    HI,
    Ondax has tested the new red diode also with good results! I pointed out your work and they are loving it…so much free testing information for them. I am working with them to put a 100 mW SLM laser on the marketplace under $5K, maybe under $4K. Great work on the Sapphire also…good information for all. Best, Phil, 142laser

  16. Jose Crespo Says:

    Thanks for the information in your site. I’m trying to change a HeNe in a speckle interferometer by laser diodes, and for months I was unable to do it by a problem with stability of fringes. With the information about diodes and single mode longitudinal regions, I take the red diode and low power to stable region, and all things OK.

    Thanks

    • rxlaser Says:

      Hi,

      thanks for telling! For sake of completeness, can you tell which diode you used and with what power (or current) you obtained single mode operation?

      Best regards,
      W.

      • Jose Crespo Says:

        RLD65PZB5. In 25mW I obtain good speckle correlation fringes in a shear arrangement. The displacement about 4 um in circular plate, off-axis arrangement. Next weeks, I’m going to mount a TEC and an arduino based controller for temp stabilization, and a photodiode for sampling and normalize the emited power and imagen obtained.
        The photodiode and meter, I want do a custom madre arrangement. Can I inquire you by mail and discuss which diode??

  17. rxlaser Says:

    Hi Jose,

    mail is ok but we can do also here. So the diode is just for monitoring power and to normalize the singnal? Virtually every diode will be ok, but better would be one with a large sampling area, let’s say at least 3mm x 3mm or more!

    How do you read the fringes?

    All the best,
    W.

    • Jose Crespo Says:

      Yes, only for normalize…
      What you see, is an specklegram, like holographic interferometry, you take a frame from object in un unstressed state, stress the object (heating, pushing) and take another frame in stressed state. Diferentiating images, you can see the correlation fringes, which are dependent from off plane deformation suffered by the object. Another approach is applying a phasehift on the first specklegram obtaining the whole phase, then stress and sabe prodedure, substracting phase in each point, and here are the fringes.
      Like holography, coherente lenght is critical point and normalization for each frame’s luminosity do better results.

      PS: Sorry, write from my iPad is vera difficult, sometimes it change word in english by another word in spanish according to the spelling… Frustrating.
      I’m preparyng a blog on speckle interferometry. Soon I will can send you a link with preliminar works and shemes of speckle interferometers.

  18. Eric Lindquist Says:

    I need a good diode laser for holography to replace my 300mw 650nm unit. Please e-mail if you can help me ibidala@gmail.com thank you
    Eric Lindquist

    • rxlaser Says:

      Hi Eric,

      sorry for late reply, well currently I am not building lasers due to lack of time. And 300mW single longitudinal mode with a 650nm diode seems very difficult to achieve even with ECDL setup, typically the
      maximum is around 100mW!

      Thanks neverlessess for your interest!
      -W

  19. Radek Sobczynski Says:

    Hi W,

    BTW, nice and impressive site.

    When you were experimenting with the HL63133DG 170mW / 638nm laser diode in ECLD configuration, did you use AR coated R<0.1% diode (facet) or it was just the original diode?

    Best Regards,
    Radek

    • rxlaser Says:

      Hello Radek,

      I use always the original diodes, mostly windowed, knowing that a coating would probably improve things, but this is out of the question for a hobbyist. At any rate, the single sample of that diode I tested was practically perfect for my purposes (I don’t need wide tuning range, etc). I don’t know whether this good behavior applies to all of those HL63133DG, or just to my sample. As a rule I found the Opnext diodes typically perform better than those form other manufacturers.

      Thanks for your interest!
      Best regards,
      W.

  20. Radek Sobczynski Says:

    Dear W,
    Thanks for your input.
    BR,
    Radek

  21. Marc Chenevier Says:

    Dear W, Your work is very interesting for me, I try to use LTC1923 to control a dfb laser temperature. I have some trouble with my power fet one of it is systematically shorted (P and N all together close on the same chip). Have you some idea about that? I use the schematic given on page 26 of LTC 1923 datasheet. Best regards.
    Marc

    • rxlaser Says:

      Hi Marc, well I just used the schematics as per the datasheet and as shown at my website, and the single sample I built had worked from the start and never gave problems. Perhaps use a multichannel scope to check the drive pulses to the Mosfets, to see whether there is any bad overlap. I vaguele remember also that there might be a component to control the dead time between pulses, perhaps there is a problem with that component.

      Good luck! Thanks for your interest!
      -W.

  22. ashok Says:

    Hi, i have tried PWM circuit (W’s simple high power PWM TEC controller) with SG2525AN with 10K NTC thermistor. But out is not coming. At pin 13 vc always high. there is not oscillation.what could be the reason. Pl. let me know. Regards, ashok

  23. Barrie Says:

    Hi W, Thanks for your quick response and some helpful answers. I am learning! It seems the shorter the wavelength of the diodes the more erratic they behave. If blue is more unstable than green and then red. Perhaps when you get down to violet below 400nm maybe they are even more unstable again. Just a couple of final questions and then I will direct my questions to the holography forum of the link you shared. I realize this is mainly a laser blog.

    I looked up your exposure time calculator for the different emulsions and the do it your self photosensor light meter. The calculator doesn’t appear to be working (page will not display), but never mind you described some calculations how you achieved such bright holograms such as your chandelier ( I assume by the color you were using the sapphire laser for these shots.) The triceratops is particularly bright. if I understand correctly your formulas for exposure are based on the quality of the plates, the type of hologram, the wavelength used, the brightness of the reference beam with consideration of the brightness of the object beam, calculated with the voltage reading of whatever particular sensor your using. Now what I would like to query and this will make a few things clear for me is. The laser after being split in to the reference beam and the object beam and allowing for the brewster angle plus using mirrors or prisms and lenses to expand the beam and cover a larger size plate obviously continues to weakens the intensity of the beam and so the more powerful the laser the less exposure time needed. Please correct me if I am wrong but holographers are wanting more wattage with as much stability from a laser as possible ? I see that portraits are shot using pulsed lasers with exposure times in nano seconds. This otherwise would not be possible because of movement. Sorry for the ramble its relative to my questions. You have suggested some exposures take 6 seconds and some up to 90 seconds for denisyuk (this is quite a length of time). If I use a very weak diode (say 1mw) to do a shot of your triceratops for instance, would I get the same result if I use an extremely long exposure? I am guessing wildly but would you have used a 20 mw laser and a 6 or 10 second exposure to get that perfect brightness on the U15 plate. What I am trying to understand is if use a weak light source and a 5 minute exposure or longer will the hologram just be washed out because of the actual weakness of the source light. Or is it because of some form of movement is inevitable on the table over a longer period of time and the hologram will not be crisp or totally vibe out ? Or is it a noise factor? There must be some reason or we could be using the stable low watt blue diodes and doing longer exposures. I remember in the early days of photography the subject had to remain still for minutes at a time to get enough exposure with the old box cameras.The pictures still came out with very good quality.
    The last question relates to the one you have already answered. The cooling fan on the DPSS laser. You suggest to ” shield the laser thermally off but keep it running”. I understand what your saying, but not quite. Is the fan on the holography table itself or beside it ? I understand you don’t want air currents around the table, but a running fan will cause vibration if its on the table wont it? Pardon my ignorance but I don’t understand how a fan or a water cooled laser for that matter wont have some movement of the table. I can see a large heat sink would be more stable but can’t grasp how a fan fits in on a holography table? I think its a fantastic idea you have your computer set up in a different room from the table. You monitor everything for stability before making your exposure. That is a goal I am going to strive for !!
    Thanks W. regards Barrie

    • rxlaser Says:

      Hello, I am currently travelling, I’ll answer later! Bests, W.

    • rxlaser Says:

      Hi Barrie,

      now I got back from travel and found time.
      Some comments:

      1) The exposure calculator did not work anymore since my web hoster
      does not allow to run programs. I may find a way around it at some point.

      2) “Please correct me if I am wrong but holographers are wanting more wattage with as much stability from a laser as possible ?”
      Yes

      3) “If I use a very weak diode (say 1mw) to do a shot of your triceratops for instance, would I get the same result if I use an extremely long exposure?”
      Basically yes

      4) “. Or is it because of some form of movement is inevitable on the table over a longer period of time and the hologram will not be crisp or totally vibe out ” This is the main problem!

      5) ” I understand what your saying, but not quite. Is the fan on the holography table itself or beside it ? ”
      No moving parts on the holo table by all means!
      But even if the fan is on a nearby table there might be some air draft reaching over. This needs to be shielded. Same for air currents created by movements. I prefer not to be in the room at all, rather I wait 10min outside before a shot, and then do it by remote control. Again, the shutter creates vibrations and therefore is off-table together with the laser.

      6) “You monitor everything for stability before making your exposure.” Indeed – I can monitor whether the laser runs stable for some while or not.

      Have fun!

      -W.

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