You now have a basic understanding of the fundamental principles underpinning the structure of longitudinal modes. Continuing our Laser Fundamentals series, the follow-up to this blog will examine a laser’s design to ensure that it operates with only a single longitudinal mode. In that article, we will cover both adding external optical elements to a traditional laser diode and modifying a laser diodes structure to allow only one mode to reach the gain threshold.

I don't think anyone can advise you on that second one unless they happen to have tried it.  It's too radical in design to even guess about.  Could be great, could be a nuisance.

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I have also seen something looking identical to the Dicfeos under other brand names, such as Qinhum, Ponacat, and ALLOMN - not your household name brands. Probably all made in the same factory.

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not sure what i would do without my visor magnifiers. but i do know i could not do much as i would not be able to see much.

For light I have a 4' daylight LED fixture hanging above the workbench, nice and bright. And i have a swing arm lamp that contains a daylight LED bulb that I can pull down to side light projects I'm working on. I also use OttLites for reading lamps by my chair, bed and desk.

I do wear glasses, so I also have one of the headset types with multiple lenses and built-in LED lights, but I've never actually used it 'in anger', the desk lamp is more than good enough.

Laser diodes must meet two critical requirements to facilitate the lasing process. The first requires that, at a minimum, the laser cavity’s gain increases to the point that it reaches unity with the level of losses. This unity state is known as the gain threshold. If you missed it, read our previous blog, titled “Laser Diode Fundamentals: Diode Gain Threshold,” to get an in-depth understanding of this phenomenon. The second requirement is that there must be a longitudinal mode present inside the optical cavity, coinciding with the laser’s gain curve. This article explores precisely what longitudinal modes are and how they affect the laser diode‘s performance.

I use a pair of reading glasses prolly #3s over my regular glasses and down on my nose so I can watch the football replays over the top. I got mine at the local supermarket pharmacy and tried on several before getting just the right ones. Very cheap.

There is only one led light, and it's centered. Dual lights over each earpiece would be a little nicer when it comes to eliminating shadows. The light can be tilted up or down  independently of the magnifier lens, which is nice. The light given off by the led spreads out more than enough and is a very white/blue color not a warm yellow color temperature light. Probably around 5000K would be my guess.

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#3 Two major problems. 1 - It is hard to work on models looking through the lens.  Too much stuff in the way.  2 - The arms are always in the way.  They are like a helix in that they need their space.

Or the kind that attaches to the table and you look through? I've got a couple of these in storage:  https://www.amazon.com/Ironton-Magnifier-Lamp-4in-Watts/dp/B07N8JP6HB

One advantage of the design is that if you have a magnifier flipped down you can look around it (look over it by pointing your nose down, or under it by tilting your head back). That is a plus vs the optivisor design which I imagine makes it a little harder to find tools on your work desk when using a high magnification lens.

Oh, and seconding what reklein says about soldering fumes - don't take unnecessary risks, always use good ventilation no matter how safe the materials are supposed to be.

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Maybe I will see if I can get a tiny cheapo fan, separately. None of these lighted-magnification headband thingies come with a fan attachment :D

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I got this light because it is fairly bright. I find that it is easier to use an Optivisor and good lighting when soldering small things like 0402 SMD LEDs. I also have an LED lit magnifier and I find myself using the Optivisor more frequently.

Being a good model railroader, I never throw anything away until it is in microscopic parts.  My lights did come from Amazon and were 2 for $30.  They are on tripods and led panels of the on/off variety.  Needed one over my work area.  Got the incandescent model from the cellar that wouldn’t work with a heavy led bulb.  Dissection and cable ties gave me a result that I really like.  I did have to remove a spring from the arms for balance.  I did the same with the other one and use it in the cellar.  Might start going to a garage sale or two now......

I use a version of number 1 because I ware glasses and #1 works with glasses.  I set it up for maximum magnification and never change it.  Once in a while I use the round magnifier.  I can ware it for hours on end with the flip up.

As for as the magnifying headsets, you might consider ordering both styles and see which style you prefer.  If you buy them through Amazon you can return the one you don’t like.  The knock-offs may be just fine verses an Optivisor- the difference is probably plastic vs. glass lenses.

Both multi-longitudinal mode and single longitudinal mode diode lasers have their inherent pros and cons. Multi-longitudinal mode diode lasers are typically more straightforward and cost-effective to produce, with the added benefit of generating much higher output powers, due to the larger number of modes. On the other hand, single longitudinal mode diode lasers have a much narrower bandwidth, making them more desirable for applications that require precise knowledge of the wavelength. However, these diode lasers typically produce much lower power and are more challenging to manufacture.

I've got two small things I need to order from Amazon anyway, and either #1 or #2 will put me over the free-shipping threshold, so I think I will go ahead and give #2 a try. If it doesn't work out I won't bother trying to return it, I'll just write a negative review :-P.

I was sort of hoping for some discussion about the comfort or ease of use between the two types I posted links to - the optivisor kind that uses a headband across your forehead with a flip-down portion like a motorcycle helmet visor, and the kind you wear like glasses with a flip-down lens like flip-up clip-on sunglasses.

Just a safety note about soldering with your nose five inches away from the solder. Use a FAN over your work area to blow fumes away.

The first one is a lot like the Optivisor, which I used constantly, couldn't be without it.  The one pictured in your link has some additional features that could be good, again, no way to guess without using it.

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I've tried quite a few magnifier and lighting solutions. The visor types just don't give my eyes what they need to focus through a depth of field without constantly moving my head.....dizzy. Obviously they work for a lot people just not for me. The several lights with a lens in the middle that I have put money into over the years have all been given away or tossed.

What do you use for light/magnification? The temporary workbench I have has terrible light - florescent can lights way overhead that cast shadows more effectively than they help me see. I need something like one of these:

It seems most people have gone for the optivisor. For the price of just the light attachment to the optivisor, let alone the optivisor itself, I can buy one of each type of knock-off to try, but which one should I start with?

I have tried lighted optivisors and found that their extra weight gives me a headache. I'd rather use a std unlit set and good aux lighting.

The #2 option says in the Amazon Q&A that it works over glasses, and also has a headband that can be used (similar to the optivisor?) instead of the ear/nose pieces. It also has various magnifications from 1.0 to 3.5, so I think I will try that one due to its versatility.

https://www.amazon.com/SE-Illuminated-Dual-Flip-Magnifier/dp/B003UCODIA/ref=zg_bs_2236129011_6?_encoding=UTF8&psc=1&refRID=6B0FCCJ9SRXAS31PCX9Q

https://www.amazon.com/Dicfeos-Headband-Magnifier-Mounted-Magnifying/dp/B075WR4M99/ref=zg_bs_2236129011_22?_encoding=UTF8&psc=1&refRID=6B0FCCJ9SRXAS31PCX9Q

I was delighted to find a magnifier with lights at Harbor Freight for a great price. They lasted approximately one minute. Instant headache!

I had a similar problem, which I initially solved with a Maplin's fluorescent desk magnifier, but the arm mount was a mite flimsy and gave up after a couple of years. I replaced it with a Chinese unit of similar design, but a bit stronger construction. I wasn't happy with the colour of the light from the fluorescent tube, though, so I replaced all the internals with a couple of 12v self-adhesive, reflectorised LED chains sold as daytime running lamps for cars, powered by a small switch-mode power supply from one of he big supply houses (I think it was Rapid Electronics, but it may well have been RS-online; it was a while ago now). I now have crisp, 6500k light and good magnification.  A look around ebay - and maybe Amazon - should throw up several similar LED units, fluorescents now being  seen as less 'environmentally friendly'.

You can acquire the specific, allowable spectral modes by superimposing the laser diode’s gain band on top of the Fabry-Perot cavity modes, as shown in the figure to the right. The laser can only produce these remaining modes (or wavelengths), referred to as the laser’s longitudinal modes. If a particular longitudinal mode’s gain is greater than the total cavity loss (the gain threshold), amplification of that mode is allowed, and lasing can occur. The interrelationship between gain threshold, gain bandwidth, and longitudinal mode spacing ultimately determines whether a diode operates as a single or multi-mode device. A laser is classified as ‘single longitudinal mode’ (SLM) when the gain threshold is significantly high, and the gain bandwidth substantially narrow, allowing for only one mode to lase. Conversely, a laser is classified as ‘multi-longitudinal mode’ (MLM) when the gain band is substantially broad and the threshold significantly low, allowing for many modes to lase at once.

One thing about it worth mentioning is that the led light takes three AAA batteries, which are housed over the bridge of the glasses underneath that Dicfeos logo, accessed from the back. That make the whole thing a bit heavy. I know they make led flashlights that work on just one AA battery, so I question their engineering choice. Perhaps using it for a long session it would begin to get heavy, but it hasn't bothered me yet as I use it in short stints, and it comes off as easy as a pair of specs. This unnecessary weight is really the only 'con' I have discovered so far. I've not tried the elastic headband, I use it in glasses-mode.

All lasers must contain three key components: an active gain medium, a resonator cavity, and an excitation/pump source. To understand what longitudinal mode is and how it’s derived, we will focus solely on the resonator cavity, ignoring the gain medium and excitation/pump source. To further clarify our initial analysis, we will also assume that both mirrors in the resonator cavity are 100% reflective, effectively giving us what’s known as an “ideal resonator.” In the simplest case, the laser’s optical cavity is formed by two opposed plane (flat) mirrors surrounding the gain medium (a plane-parallel or Fabry–Pérot cavity). In this scenario, all light waves are trapped within the cavity, creating a standing wave as the light propagates and reflects between the two mirrors. For a better conceptualization, think of how guitar strings can sustain the same note or frequency, resulting from the wave propagating along the medium and reflecting off the string’s fixed ends (standing waves).

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I ended up buying the Dicfeos (how do you say that?) headband/magnifier linked in the OP as the second link. I thought I'd write a little mini-review.

One helpful comment in the thread was about not wanting to hold everything 5" away. That's true for me to, I'm doing soldering in a fast tracks jig on the table, I can't be holding stuff up in the air and I don't want to have to bend over within 5" and singe my mustache. So I am putting some stock on the fact that the #2 choice has changeable lenses.

I use the Optivisor from Micromark, magnification is good, vision is sharp and fully 3D at the right viewing distance and the headband is quite comfortable.  I find it very easy to use because just a quick push with one hand is all that is needed to move it, so I don't even need to put down what I am holding, whereas with glasses I need the full use of the fingers of one hand and often even both hands to manipulate reading glasses.

I wear glasses and have used an Optivisor for years with no fit or interference issues. I like the security of the headband and that the sides of the act like blinders which helps my concentration; but that’s just a personal preference.  Mine is an older version with incandescent lights on the side but I found they didn’t help much and I don’t use them.

6. Can be used for vehicle headlights in an emergency. Please be courteous to oncoming traffic and remember to switch to lo-beam and avert your gaze.

I started with the 1.0x lens, and then skipped over the 1.5x to try the 2.0x. The 2.0 is definitely enough for my HO-scale modelling purposes, I don't need the higher powered lenses that are included.

Light really helps. I have an older Ott light and it's frequently good enough to allow me not to wear my optivisor. A friend has a newer one but I haven't tried it yet. Having the big magnifying thingy on a light between me and my work is a problem for me. I used that when I had a brief career in manufacturing and it always seemed in the way.

For general lighting I have two swing arm lights, one each side of my workbench.  One is a plain light and the other has the magnifier lens, both with LED lamps. I occasionally use the magnifier on the lamp, but could get along just just fine without it.  When I visit family in northern California have access to a floor stand Ott Light with a magnifier and the light it puts out is great but, again, I rarely use the magnifying lens.

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I'm not soldering 5" away, that's the point. So I don't want something that forces that distance to get things in focus. So I do want something with variable magnification so I can get the right distance - more than 5".

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Given this quantization of suitable frequencies/wavelengths in the laser resonator cavity, we can see that an infinite number of modes can fit into the resonator, all with equal frequency spacing. These Fabry-Perot modes, as they’re called, heavily influence the laser’s spectral characteristics. However, no mirror is 100% reflective, and if they were, you couldn’t use them to generate a laser beam. A cavity with 100% reflective mirrors would block all transmission of light, making it impossible to output a usable beam. Since all practical resonator cavities will exhibit some loss at the mirrors, the Fabry-Perot modes can not be pure delta functions; rather, they have an inherent line width that varies based on their reflectivity percentage. A detailed analysis of the causes of this line broadening is beyond the scope of this blog post. However, the figure below illustrates the effects mirror reflectivity has on the mode structure.

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They are light weight, offer different lenses for different magnification, easy to swing up out of the way or readjust to see something. I can wear them over my regular glasses. They work with the bifocals. But what I like best is I can look over the top to see what is on the shelf above the work bench or to glance at the plans or tools just out of reach. OR even to speak to the wife when she comes into the train room. These were designed by a lady for needle work.I bought mine in the sewing department at Hobby Lobby.

I think for less than $15 it's got to be a better buy than the optivisor, though I've never tried an optivisor. I just can't imagine what would make the optivisor multiple times better to justify it's multiple-times-greater price.

I found an inexpensive flip down magnifier at Harbor Freight that clips onto ones glasses. It gives about 3x magnification for just general use.

I haven't used it a lot yet, but I find it comfortable to wear. It has a rubber pad where it rests against your forehead, that and the ears and nose supports take the weight. The rubber pad is textured and a little bit soft.

I do have glasses, but i'm slightly nearsighted so I usually take them off indoors. I will give the thing I buy a try with the glasses and post on here for all posteriors, er, posterity.