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Audio/RF amplification using lasers? (crazy idea time)

Discussion in 'General Electronics' started by Jon Noring, Jul 12, 2003.

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  1. Jon Noring

    Jon Noring Guest

    A crazy and, more likely than not, stupid idea (and which no doubt has
    crossed the minds of others) hit me as I thought about amplifying weak
    audio and RF/audio signals. The usual technologies for amplification
    include tubes and transistors. Why cannot lasers be used for electronic
    signal amplification? (Maybe they have, but I have not yet found any
    discussion/information on such devices...) Let me explain what I mean:

    In triode tubes, for example, when a weak input signal is applied to
    the control grid, it regulates the higher-power current flow from the
    plate to anode. Amplification of the signal is achieved.

    If we now visualize the laser analog to the triode, where we replace
    the current flow from plate to anode with a high-power continuous
    laser beam directed at a spot photocell, and replace the control grid
    by something else which modulates or deflects the laser beam based on
    the weak input signal, then in essence we can (at least as I see it)
    potentially achieve a very high gain of the input signal, and, if
    properly and cleverly designed, may also achieve quite linear, low
    distortion, low-noise response. It may open up new possibilities for
    high-end audio components (amps, phono-amps, radio tuners, etc.) and
    for various scientific applications where space/weight is not a
    critical factor.

    For example, in the simplest "mechanical" analog of this system,
    imagine a higher-power laser beam directed at a photocell via a small
    reflecting mirror. By applying to the mirror the weak input signal so
    as to somehow deflect it a tiny bit, we can effect quite large
    deviations of the reflected laser beam directed at the photocell
    target. The photocell would then output a much higher powered signal
    modulated by the weak input signal.

    There may also be "non-mechanical" ways to modulate/deflect the laser
    beam, but I do not have any concrete ideas regarding those.

    So, is there a fundamental problem with this idea? (Of course, there's
    lots of real world issues, such as vibration and inertia issues for
    mechanical type of modulation, and various inherent sources of noise.)
    Has anyone done research and development in this area, possibly even
    marketing a product which accomplishes pretty much as described above?

    As my graduate advisor once told me: "A person can think of a thousand
    reasons why something won't work, but all you have to do is think of
    ONE way to make it work."

    I look forward your thoughts and, of course, criticisms on this nutty

    Jon Noring
  2. Charles Jean

    Charles Jean Guest


    How about the laser beam shining through what amounts to one segment
    of an LCD, and modulate that? Is it possible to turn a segment
    "partially" on? I guess what I'm really talking about here is an
    electronically variable light filter. Doesn't Bill Gates have
    something like this on his house windows?
    (Another thought: a rotating polarized filter might produce a very
    clean sine wave in the audio range.)

    If God hadn't intended us to eat animals,
    He wouldn't have made them out of MEAT! - John Cleese
  3. DarkMatter

    DarkMatter Guest

    The "Optical Transistor" is the only ting eluding us from building
    an optical computer. A mere 4-bit version of which would toast
    anything you ever laid your hands on by an order of magnitude.
  4. Mathew Orman

    Mathew Orman Guest

    Lasers are oscillators and when used as an amplifiers there ware found to be
    very unstable.
    So instead the Erbium Doped fiber amplifiers are in use now for amplifying
    Search for more data using keywords +"optical amplifiers"+"laser"


    Mathew Orman
  5. Mike Poulton

    Mike Poulton Guest

    Huh? Lasers can be oscillators or amplifiers. LASER means "light
    AMPLIFICATION by stimulated emission of radiation" -- whether configured as
    an amplifier or an oscillator, it's still a laser. An EDFA is a type of
    laser which happens to be a very good amplifier. Some other types of
    lasers don't make good amplifiers, usually because the gain is too low
    (argon ion, for instance). "Stability", whatever that means, is
    irrelevant. Non-oscillating "gain blocks" are common in high power pulsed
    laser systems, like NOVA and the National Ignition Facility. A Q-switched
    seed laser is used to feed many stages of Nd:YAG or Nd:glass slabs that act
    as laser amplifiers, with high enough gain to be completely depleted in one
    pulse. This allows the production of narrow pulses (Q-switched pulse
    widths) at power levels that would annihilate any Q-switch. Very handy.

    Mike Poulton
    MTP Technologies

    Live free or die!

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    even close to sufficient reason.
  6. I think the original question was more along the lines of why lasers aren't
    used in place of more conventional amplifiers at audio and RF frequencies.
    Aside from noise and stability issues, the simple answer is that there are
    very good simple electronic means of amplifying electronic signals up through
    microwave frequencies. It's hard to beat 40 dB of gain from a 10 cent
    transistor circuit. :)

    --- sam | Sci.Electronics.Repair FAQ Home Page:
    Repair | Main Table of Contents:
    +Lasers | Sam's Laser FAQ:
    | Mirror Site Info:

    Important: The email address in this message header may no longer work. To
    contact me, please use the Feedback Form at Thanks.
  7. Subhajit Sen

    Subhajit Sen Guest

    There will always be applications in which the fundamental
    noise mechanisms (kT/R for thermal noise and IkT for shot noise)
    of electronic systems will be obstacles to amplification and
    detection(detection of gravity waves for example). Trying
    out lasers or other optical means may be a
    smart idea but I have no clue as to how they would work.

    Subhajit Sen
  8. Jon Noring

    Jon Noring Guest

    Yes. This is not for optical amplification, but simply to use the unique
    properties (coherence, collimation, etc.) of laser light as noted. It's
    akin to using a laser for land surveying, burning off unwanted hair, etc.
    -- just another application of lasers using its unique properties.

    Well, of course. But if 10 cent transistors were adequate for
    everything, then everything would be built with 10 cent transistors.
    Last I looked, tube-based amplifiers have been making a steady
    comeback in the audiophile community.

    I simply wish to explore this idea, whether proven silly or not, since
    the *potentially* very high gain, high linearity, and low distortion,
    are very intriguing, especially for the audiophile community (and
    maybe for certain scientific applications). Of course, like anything,
    when one moves an idea from concept to implementation, things like
    "reality" rears its ugly head. <laugh/>

    I think the questions to ask of this idea is *how* one could build at
    least an audio signal amplifier using a lasers as I previously
    described (I focused on mechanical means, such as a movable mirror to
    deflect the beam, but other types of beam attenuation are also
    possible), and what the potential gain, linearity, distortion and
    noise would be. Be creative -- don't let current reality get in the
    way. It might turn out that with the right set of clever solutions,
    one may find a use regime (albeit specialized) where the electronic
    equivalents of transistors and tubes are not competitive.

    Jon Noring
  9. But not in low noise high linearity systems. In many systems, low noise
    or otherwise, $0.10 would be highway robbery for a transistor. In
    applications I worry about, transistors are free
    For audiophiles, don't worry about signal quality metrics. If you can
    sell snake oil, you can sell audio.
    If you wish to amplify electronic signals, you have the problem that the
    input impedance of the amplifier dominates system noise. Generally, you
    can expect all noise in this type of system to be sensor intrinsic noise
    or input noise. How does a laser get around these?

    In a sense, there are "laser amplifiers" of the type you mean in use.
    For example, CD and DVD focus and tracking methods use a laser and
    photodiode sensors to obtain electical signals proportional to error
    from desired focus and position. The measurement noise is dominated by
    the shot noise in the photodiodes. That is, the electronic amplifiers
    following the detectors need not be especially low noise in the focus
    and tracking paths. The sensor equivalent noise of a $0.10 operational
    amplifier might be just a couple of nanometers while the sensor noise
    might be 10X that.

  10. Yes laugh, since I designed (in the long ago past) both tube amps
    (for a band for example) and transistor amps (in the more recent past),
    I can tell you that the one that suggested to you the tube amps were:
    'more linear, more robust, more (whatever good)', was at least lying.
    I have never, even for 2 milli seconds, longed back for the 807 push pull
    zero bias stage after I build my first SEPP transistor output.
    And that was in 1968
    Since then transistors have improved a lot.
    The choice of tubes has decreased a lot.

    And, as mentioned by Sam, a 10 cent transistor is a good
    solution as it requires low overhead (power supply, whatever you are
    going to need for the laser).
    In fact at light frequencies, of cause you could FM modulate a YAG
    (or whatever it was called) laser, mm maybe mechanically ;-) and then
    use frequency doubling, that would double the deviation, then somehow
    detect it.
    Audio is at lower frequencies then light, maybe mix it up a bit?
    Really are you trying to create an other nonsense-market (after tube amps)?
    Use the laser for what the laser is good at, and the transistor for what it
    is good at.
  11. In fact, this is the sort of research I'm involved in. But it's to FM
    modulate a laser at microwave and higher frequencies for use in fiberoptic
    networks, lidar/radar, and medical imaging. With these, the unique properties
    of lasers are essential.
    Yep. :)

    --- sam | Sci.Electronics.Repair FAQ Home Page:
    Repair | Main Table of Contents:
    +Lasers | Sam's Laser FAQ:
    | Mirror Site Info:

    Important: The email address in this message header may no longer work. To
    contact me, please use the Feedback Form at Thanks.
  12. Mark Johnson

    Mark Johnson Guest

    Hi, people.

    Although not really related to the topic at hand, this thread brought
    to mind the new technology called Hypersonic Sound, which I first read
    about around a month or so ago in one of my engineering magazines
    (either Electronic Design News or Design News).

    It's kind of like "laser" sound waves. If you haven't yet read about
    it, I think regulars to alt.lasers will enjoy the short read at the
    links below:,16106,388134,00.html

    I'm wondering how this could be used for laser shows!!!
  13. Skywise

    Skywise Guest

    (Mark Johnson) wrote in
    DAMNIT!!!! I am too slow...I had this idea YEARS ago....oh well....
    glad to see it developed would allow the use I
    originally had it in mind for....although I think I'll wait for
    the price to drop a bit first.

    I originally thought of using ultrasonic transducors at different
    frequencies to set up a 'beat' frequency when the ultrasonic waves
    struck an object, specifically a car. That way I could tell that
    driver very specifically what I thought of their driving without
    it being broadcast to everyone else at the same time. The target
    driver would not be able to tell where is was coming from since
    the sound would be emenating from their own vehicle.

  14. Mark Johnson

    Mark Johnson Guest

    Don't you just HATE it when that happens?!?!
    That's an absolute FANTASTIC use for this...why didn't I think of it?
    Especially after (just this morning!) being one of around 15 other
    vehicles stuck behind a woman driving an SUV kinda slow in the fast
    lane. People were going around her in the middle lane, and when I
    passed her, she was yacking on her cell phone. I honked my horn, and
    she just honked back. I recognized her from another day, doing the
    same thing, even to talking on the cell phone. Yep, I honked then

    I would LOVE to be able to tell her what I think (I wonder if the
    person she's talking to on the cell phone would hear?), instead
    of...errrr...the other way I let her know how I feel. I know, that's
    bad, but I drive 30 miles each way, with around 10 miles in
    construction (last 2 years!!!), and it's so incredibly rude to
    intentionally interfere and hassle with other people who simply want
    to get where they're going.

    I swear, I think that even the world's rotation slows down when I'm
    stuck behind one of these morons.

    It sounds like YOU have this problem too, eh??
  15. Skywise

    Skywise Guest

    (Mark Johnson) wrote in
    I have had this problem ever since I started driving. I
    live in the LA suburbs....I used to get pretty ticked in
    driving at times. But I've forced myself into some new
    tactics and it's lowered my blood pressure quite a bit.

    What I do depends on if I'm in my car or on my bike. On
    the bike I pretty much do whatever I want on the road
    simply to keep myself as far away from any other vehicles
    as possible. Safety first, laws second. Once I realized
    a few tricks my 'close encounters' have dwindled
    dramatically. I have quite a rule list (which I ought
    to write down someday) but probably number one is "always
    go faster than those around you." Does wonders, and I've
    even had motor officers agree with me.

    In the car I'm much more subdued. A lot of times if
    someone cuts me off I just go around them...maybe change
    lanes right back in front of them, and I'm over it. Or
    sometimes I'll see someone being a not-so-good driver
    and I'll toy around with them a bit; like speeding up
    and slowing down at appropriate times so they can't
    slalom their way through traffic like they are so
    obviously and desperately trying to do.

    Fortunately I'm one of those individuals that becomes one
    with the vehicle I'm operating so my reflexes are pretty
    damned quick. I've startled myself a few times at how I
    just simply went around something and then thought later
    "how did I know to do that?"

    And in case anyone is wondering, I have only ever had two
    tickets in 16 years of driving and 3 accidents, none of
    which was my fault.

    If you've read this far, sorry this was so off topic.
    It was just a chance to gripe a little. I really could
    go on and on about bad drivers.

  16. Cory B

    Cory B Guest

    Might I suggest using a 60mW DPSS green pointer from spacecoast
    electronics to flash blind the idiot instead of shooting him? It's
    not legal, but it's not looked down on quite as bad as shooting the
    idiot. Not to mention you don't have to shoot one of your windows
    out... Just a thought....
  17. Skywise

    Skywise Guest

    Sheeet!!! If someone ever does that to me when I'm on my bike
    I'll be getting their license plate and charging them with
    assault with a deadly weapon.

    For the other posters, I've thought of various laser devices
    to use but ruled them all out as there was no way to
    guarantee that innocent bystanders would not be placed in
    harms way.

  18. You're part of the problem, NOT the solution.
  19. LA Sucks.

    You suck

  20. Some Guy

    Some Guy Guest

    Uh, FYI: they have a name for drivers that try to control or punish other
    drivers in this (or any other) fashion. The name is: VIGILANTE. And in
    case you didn't know, being a vigilante is ILLEGAL. You should be ashamed.
    You should be arrested. You should have your license revoked simply based
    on this confession of lawbreaking. At least you aren't one of those jerks
    who will straddle two lanes in an effort to keep people from passing them in
    the merge lane at a road construction site. Or are you......?

    Also, you should be made aware that the safest place to be when confronted
    with one of those in-a-hurry not-so-good drivers is BEHIND them... so you
    can keep an eye on them, and will have time to react if they do cause an
    accident. If you are such a good driver, you should be making it easier for
    them to get past you, not harder. I would never act in such a way as to
    remain in front of a driver I considered to be a hazard.
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