Laser pointer for start viewing: something affordable?

[dotancohen]

I have a cheap $8 USD 5mW green laser for pointing out stars to my daughters and neighbours. This laser does not have a safety rating on it, so I treat it as a class 3. It is getting weak and I need to replace it.

My first thought was to order from Wicked Lasers [1], who had been recommended to me in the past. However, their 5mW green laser costs $30 USD plus another $18 for shipping. I simply cannot afford that. So, are there any lower-cost quality lasers available? What do the community members around here use?

Thanks.

[1] http://www.wickedlasers.com/lasers/Core_Series-67-3.html

 

[Drakkith]

Is it getting weaker because the battery is dying or because the laser is degrading somehow?

 

[dotancohen]

Fresh batteries do not increase the brightness, so I suspect that either the laser component itself or something else is degrading. I'm not qualified to open it up myself and check.

 

[mp3car]

Looks like you can find green pointers on amazon.com for decent prices (~$10) some of them with free shipping... keep in mind, green pointers that advertised 10mw, 30mw, 50, 100, etc. are likely the same hardware, the laser diode's current is just pushed up - a lot in some cases - which shortens the life. Are you sure yours was actually emitting 5mW and not more? 5mW is enough to use for stars, but not nearly as good as 20mW or more, and since yours didn't have a safety label on it, i wonder if it was higher than 5mW output.

Just be happy they're so cheap now... I purchased my first green pointer in approximately 1996 for $400... my first red pointer was about $120.

One last tidbit which you may or may not know, or care about... green laser pointers use an IR laser diode to drive other optical components, which ultimately end up emitting green.

 

[Meatball]

Avoid Wicked lasers at all cost.

All talk and no walk.

If you want visibility, 15-50mws will be just fine assuming you keep with the 532nm wavelength. If you're in no hurry, o-like.com has provided up to spec pointers for very reasonable prices, as well as customer support. They do NOT have IR filters on their models unless otherwise specified, so you know the drill. No pointing at things you wouldn't fire a 50 cal at.

You should not have to spend more than $1/mw for a green laser for your application.

 

[Drakkith]

Fresh batteries do not increase the brightness, so I suspect that either the laser component itself or something else is degrading. I'm not qualified to open it up myself and check.

Are you sure? I'm almost certain I've had a laser pointer in the past that lost brightness as the battery ran down.

 

[dotancohen]

Looks like you can find green pointers on amazon.com for decent prices (~$10) some of them with free shipping... keep in mind, green pointers that advertised 10mw, 30mw, 50, 100, etc. are likely the same hardware, the laser diode's current is just pushed up - a lot in some cases - which shortens the life. Are you sure yours was actually emitting 5mW and not more? 5mW is enough to use for stars, but not nearly as good as 20mW or more, and since yours didn't have a safety label on it, i wonder if it was higher than 5mW output.

It may have been putting out more than 5mW, I have no way of testing that. The laser was very bright when new, very clear and distinctive. Now, even with fresh batteries, the laser is so dim that my observers have difficulty discerning the beam. Even if they see part of the beam, it is not clear at which star it ends.

I looked at laser pointers on Amazon, and they all seem to be the same non-rated Chinese model that I have, the housing and even the case are the same. And one user mentioned the dimming of the laser device after some use:
https://encrypted.google.com/url?sa=t&source=web&cd=1&ved=0CBMQFjAA&url=http%3A%2F%2Fwww.amazon.com%2Fgp%2Fcustomer-media%2Fproduct-gallery%2FB001AAVVM0%3Fie%3DUTF8%26totalImages%3D49%26pageSize%3D10%26sort%3Dnewest%26currentImagePage%3D0%26currentImagePageOffset%3D6%26currentImageID%3Dmo2BFF8DU3M2S02%26action%3DsetImg%26page%3D0&ei=b8O3TdqJB4W2hAeclsX3Dg&usg=AFQjCNHqpsqvpgJCoRXve81Zffoy3lpm-g&sig2=I6blhAY1ftERxGAh55IGxA

Just be happy they're so cheap now... I purchased my first green pointer in approximately 1996 for $400... my first red pointer was about $120.

I do remember those times. Here (Israel) the prices were roughly double that!

One last tidbit which you may or may not know, or care about... green laser pointers use an IR laser diode to drive other optical components, which ultimately end up emitting green.

Yes, and this is very dangerous because the IR leaks out and does not cause the blink response. I have heard that the IR can leak out in a much wider cone than the visible spectrum, but I do not know if it is true. It sounds plausible if the IR is non-coherent (but I think that it should in fact be coherent). If I'm not mistaken, a 532 nm green laser uses a 1064 nm diode, then some polarised crystal to half that?

Are these non-rated no-IR-filter green lasers on Amazon dangerous? Would I be better off with a purple or red laser that uses a visible-light diode and thus has no IR leak?

Thanks!

 

[Drakkith]

Yes, watch out for some pointers. Some do not have a filter in them that would remove the IR light. In all cases you should ALWAYS avoid pointing the laser pointer anywhere near someones face. As long as you keep proper control over it and no one abuses it you should not run into any problems even if it does "leak" IR out. But it's up to you whether you want to risk it.

 

[dotancohen]

Avoid Wicked lasers at all cost.

All talk and no walk.

If you want visibility, 15-50mws will be just fine assuming you keep with the 532nm wavelength. If you're in no hurry, o-like.com has provided up to spec pointers for very reasonable prices, as well as customer support. They do NOT have IR filters on their models unless otherwise specified, so you know the drill. No pointing at things you wouldn't fire a 50 cal at.

You should not have to spend more than $1/mw for a green laser for your application.

Thanks. That site seems to have the same lasers that I have, and certainly don't address the IR concern that led me to question their use. Do most astronomy use-cases use non-rated, no-IR-filter green lasers like this?

Are you sure? I'm almost certain I've had a laser pointer in the past that lost brightness as the battery ran down.

The laser most certainly loses brightness as the battery wears down, but it's fresh-battery brightness is now less than the threshold change-the-battery brightness of the same device when new. In other words, if the brightness-to-charge graph of the laser when new was similar to the torque graph of a Tesla S roadster, then the brightness-to-charge graph of the laser in it's current shape is similar to the torque graph of a pencil sharpner.

 

[Drakkith]

The laser most certainly loses brightness as the battery wears down, but it's fresh-battery brightness is now less than the threshold change-the-battery brightness of the same device when new. In other words, if the brightness-to-charge graph of the laser when new was similar to the torque graph of a Tesla S roadster, then the brightness-to-charge graph of the laser in it's current shape is similar to the torque graph of a pencil sharpner.

Oh, ok, my mistake. Now I understand what you are saying. I misunderstood your 2nd post.

 

[Meatball]

Most astronomy pointers aren't rated because their not necessarily your most higher power greenies available. Because they can be made cheaply, it turns out China ends up being a source for many if not most DPSS laser manufacturers. These pointers are sold on sites like pandawill.com, tmart.com, dealextreme.com etc...

Cheap websites.

You CAN buy high quality, spec'd, and IR filtered pointers though. They simply cost more.

Optotronics is a popular reseller of handpicked Viasho products. Laserglow is a popular CNI retailer. Each of the sellers can sell you a pointer with more guarantees.

But to be honest, I only pointed you to o-like.com because they are a balance between China cheap, not non-Chinese customer service/guarantees. And they also manufacture their own products. Not sure if that's why they're a bit cheaper? If they send you a laser not up to spec, you can send it back and they'll send out a replacement.

A cheap DX China laser can, (not always) be resold as a higher power module. This does cause the non-linear optics inside to degrade rather quickly. A quality greenie should remain up to spec for about 5000 hours of CW use.

When the pump diode is driven too high, it begins wasting light on the YAG as heat. These heating and cooling cycles cause instability in power, mode hopping, and even the structural failure of the crystal.

Your older pointer has simply degraded. No big deal, a simple replacement will do.

Again, I recommend 15-20mws for complete darkness use. And no more than 50mws for times just after dusk and before dawn.

ALWAYS watch out for aircraft of all kinds! You will be caught and prosecuted for endangering lives. The Feds care little about the legit reason's "why" you were spitting coherent photons near a plane. If the see your beam, pilots have to report its presence, and its location. So that everyone here knows, be careful!

Though being an experienced star pointer, I'm sure you are!

 

[mp3car]

I thought of another thing last night that can lower brightness... have you dropped it? Since, as Meatball eluded to, I believe still to this day, green lasers (solid-state, non-gaseous green lasers - yes, HeNe can be tuned for green, and I believe yellow and orange emission too, not just red) are all pumped by a high power (200-500mw or more) IR laser diode, 808nm... this "pumps" a YAG crystal to lase 1064nm (I assume they do this b/c high power ~1064nm IR diodes are more expensive than the YAG crystal??), which is then frequency doubled (cuts wavelength in half) to produce 532nm, green. This process is fairly inefficient, so you may have a 200mw IR diode that ends up coming out as 5mw of green wavelength. I have only owned two, and both had IR cut windows on the end, it's the last optic in the line, usually square and slightly purple/blueish tinted when you angle it, a very thin glass element.

Anyhow, back to my question, did you drop it? My first one (the $400 5mw I mentioned in my first post) decreased significantly in power after i dropped it one time, presumably b/c the optics got out of alignment. I did not try to repair it since they are cheap now). the second one I bought (sold as a 5mw, but i cranked it up to XXmw) began to degrade after probably a few hundred hours of use because i cranked it up to who knows how many mw, but it would pop dark colored baloons (after i increased the power) and also get quite warm on your skin, especially more tanned areas like the back of your hand/arm.

Another thought, i suppose they could omit the YAG crystal and have a 404nm violet laser, but i guess that would be a waste since blue and violet diode lasers are actually blue or violet laser diodes... this reminds me of the other physorg article i read a few days ago about a recent advancement in green LED manufacturing... maybe it will help improve the green laser diode... I suspect that would increase the battery life significantly of green pointers.

 

[Meatball]

Dropping a DPSS is generally very bad. If the any of the optics, or pump sources get misaligned by even a fraction of a mm, you can lose phasing, power density, mode control, and proper collimation.

A YAG/KTP based 532nm DPSS system will typically land between 20-25% efficient via light power out over light power in. So a 1W pump diode can typically be the source of 200-250mws of green light. On a high end system, 300mws is not unheard of.

I will directly quote an explanation I once read, that best describes why YAG is still used, and why 405nm laser diodes are still a better option than directly doubling an 808nm laser diode. You can buy a 1064nm laser diode, but it can't pump a KTP because of its relatively wide bandwidth, non gaussian beam profile, and the lack of the ability to achieve a 50um wide beam with geometric optics.

The explanation excludes the fact that laser diodes are not perfectly monochromatic, whereas to get doubling, two photons with the exact same wavelength must be phased within the KTP before you convince any green photons to come out.

"Unfortunately, with KTP, it isn't simply dumping power into one end and watching it poop[word modified] out a stream of photons through the other.

Several issues come into play here; power density is one of the most obvious. You might think that 2.5W seems like a lot of power, but frankly, it isn't. Second harmonic generation (frequency doubling) has an extremely non-linear efficiency curve- the higher the power, the higher the conversion efficiency becomes. If the power density is too low, you won't get anything out at all.

To put it into perspective, your dinky 5mW green pen laser has WATTS of intracavity power at any given point. Said power is concentrated as a spot that's micrometers wide.

Shooting a diode through a KTP doubler won't get the power density you need, and not only because it makes one pass through the cavity.

Remember that power density is a combination of area and power- in the pen laser, the 1064 beam is only micrometers wide. With a diode, the spot will be significantly bigger.

Now, assuming you got the diode down to a small enough point, you'll also have issues with phase-matching the diode to the KTP. Considering that most diodes at that power are horrible multi-mode, multi-emitter devices, it certainly won't be easy. And assuming you could phase-match it perfectly (which is damn near impossible), it'd be just as hard to get the power density needed.

Anyone remember the directly-doubled Novalux Proteras? They used a special VESCEL diode (which produced a clean, Gaussian beam with very little astigmatism), which also had an external cavity. The cavity didn't just cover the laser diode itself; the doubling optic, the LBO crystal, was also part of the cavity. Consequently, the power within the cavity was higher by magnitudes than not only what was being pumped in, but also what was being emitted. Those diodes are extremely sensitive, but it was the only way to achieve direct doubling.

So, assuming you had an external-cavity, single-emitter 2.5W 808nm diode, you have a slightly bigger problem.

KTP is a glitch. By some quirk, it's brutally efficient at doubling 1064nm. By the same quirk, it can't be phase-matched to double below approximately 500nm, and it won't double at all below 490nm (if I remember correctly).

Consequently, you're left with other options including LBO (which is annoying to work with for more reasons than one) and BBO. Neither of them have the efficiency of KTP."

-Goninanblood from Laserpointerforums from thread "DPSS violet?" Post #3 on 4-26-11

I hope this covers it reasonably well..

this reminds me of the other physorg article i read a few days ago about a recent advancement in green LED manufacturing... maybe it will help improve the green laser diode... I suspect that would increase the battery life significantly of green pointers.

Green diodes are being developed in the 515-529nm range.

The only info I really have so far, shows that the 515nm diodes are single mode, maxing out at 50mws at 400mA...

horrible efficiency still, but it will get better.

 

[riquel2me]

I saw many astronomy laser pointers under $20 on amazon.com