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Laser experiment

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laserstudent

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I am a student doing an experiment that involves lasers. I am trying to determine the optimal wavelength of laser that will pop a balloon in the least amount of time at different distances. I was thinking of setting up my experiment as three rows of black balloons, one row for one particular color (wavelength) of laser (which will be red, green, and blue), and measuring the time it takes for each laser to get through the rows of balloons (pop the balloons all the way to the end). My assumption is that at shorter distances, the blue laser will pop the balloons the fastest due to higher energy of its photons and the red laser will be the slowest. As the distance between the lasers and the balloons gets larger, the blue laser will take a longer time to pop the balloons due to its shorter penetration depth through the air and the red laser will take relatively shorter time to pop the balloons due to its relatively larger penetration depth. So at some time, the red laser will catch up to the blue laser as they both make their way popping through the line of balloons. For this particular experiment, I want to keep the wattage of the three lasers equal.

My question is, what approximate laser wattage range should I use for the lasers such that a) I can see the difference in the rate of popping by the three lasers, and b) I can see the differential effect of laser energy travel (penetration) distance for the red, green and the blue laser. Preferably, I am hoping to be able to see the laser beam travel distance difference, somewhere in a 1 to 10 meter range.

Subsequently, I would like to know where I can buy the red, green, and blue lasers to do this experiment. I would like to buy diode assemblies (diode + lens) with the drivers attached. I would also like to know how to power these lasers.

Any help would be greatly appreciated. Thanks.
 





It would have been better if you used your first post to introduce yourself. Members are more likely to help you if you tell us a little about yourself and where you live.

Your experiment is a failure before you even get started as the power of the laser is the same for each laser regardless of wavelength. The power density of your beam is far more important than its wavelength. The smaller the beam profile for a certain power laser makes it more able to pop the black balloons. For this, I would use a BDR-209 laser diode which is ~405nm, but is a single mode diode with a tight divergence. If you drive it at 550 mA you should get around 800 mW of power out, but the dot will be smaller than another diode at that power because it is the only single mode diode that can be driven to that much power. If you had another single mode diode of any visible wavelength at that power it would work just as well.
 
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Paul if he ran a set of diodes at the same wattage, and assuming he kept the lens at a certain standard of focus to have similar power dens. Would then he be able to compare the effects of the spectral power of having a blue laser pop through something much faster or at a further distance than a red laser. Or is the difference of the wavelength at the same power not enough of a difference to test easily?
Also learning with him..
Thanks for the response!
 
laserstudent said:
I am a student doing an experiment that involves lasers. I am trying to determine the optimal wavelength of laser that will pop a balloon in the least amount of time at different distances. I was thinking of setting up my experiment as three rows of black balloons, one row for one particular color (wavelength) of laser (which will be red, green, and blue), and measuring the time it takes for each laser to get through the rows of balloons (pop the balloons all the way to the end). My assumption is that at shorter distances, the blue laser will pop the balloons the fastest due to higher energy of its photons and the red laser will be the slowest. As the distance between the lasers and the balloons gets larger, the blue laser will take a longer time to pop the balloons due to its shorter penetration depth through the air and the red laser will take relatively shorter time to pop the balloons due to its relatively larger penetration depth. So at some time, the red laser will catch up to the blue laser as they both make their way popping through the line of balloons. For this particular experiment, I want to keep the wattage of the three lasers equal.


Any help would be greatly appreciated. Thanks.
Click to expand...

The energy of the individual photons does not matter, only the power matters, more specifically the power density. A red and a blue laser at the same power just emit different amounts of photons, the red emitting more. You can calculate the difference easily.

The distance will not make a difference, at the distances you'd need to see a difference you wouldn't be able to pop a balloon.

You need to take into account the beam specs, for this experiment to work each beam would need to have an identical divergence, geometry and power output. Assuming you'd see a difference in the first place.

You'd also need to adjust for the slightly different absorption at each wavelength for the balloons you are using.
 
The only affect wavelength would have on the speed of popping balloons would be its absorption/reflection depending on the color of the balloon. For example, my 180mW 638nm can't easily pop a red balloon or a clear balloon, but will readily pop the other colors. It seems though this effect doesn't matter after a high enough power density is reached, as my 1.8 watt 445nm will instantly pop any balloon, even clear ones.
 
Blarg King said:
The only affect wavelength would have on the speed of popping balloons would be its absorption/reflection depending on the color of the balloon. For example, my 180mW 638nm can't easily pop a red balloon or a clear balloon, but will readily pop the other colors. It seems though this effect doesn't matter after a high enough power density is reached, as my 1.8 watt 445nm will instantly pop any balloon, even clear ones.
Click to expand...

Not entirely true, a lower wavelength beam can be focused to a smaller point and thus achieve a higher power density, so absorption isn't the only wavelength dependent effect.
 
diachi said:
Not entirely true, a lower wavelength beam can be focused to a smaller point and thus achieve a higher power density, so absorption isn't the only wavelength dependent effect.
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True. I was just thinking if they were all focused the same and had the same output in mW.
 
If you'll notice in my first post the use of black balloons, this negates the need for absorption of different colored balloons. Black balloons will make all things equal in this experiment. I still have some from years ago. You can get them on eBay dirt cheap.
 
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paul1598419 said:
If you'll notice in my first post the use of black balloons, this negates the need for absorption of different colored balloons. Black balloons will make all things equal in this experiment. I still have some from years ago. You can get them on eBay dirt cheap.
Click to expand...


You'll find that the absorption isn't flat across the whole visible range, the difference won't be massive for most of the range but if you really want to be scientific then it's something you'd account for.
 
Oh, I'm sure there is a small difference among wavelengths being absorbed by black balloons as they aren't totally black, but I believe it is negligible. I think for all intents and purposes, one can assume all visible wavelengths to be equally absorbed.
 
paul1598419 said:
I think for all intents and purposes, one can assume all visible wavelengths to be equally absorbed.
Click to expand...

Not when all variables are held constant besides wavelength. And I think that's what OP is trying to do. A percent or two would make a difference.
 
No, he's trying to find out if a wavelength of a laser at equal powers will have greater energy to pop balloons with. It won't. He assumed that the blue wavelength laser at 1 watt would pop balloons faster than a red laser at 1 watt, all other things being equal. One watt of power is one watt.
 
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paul1598419 said:
No, he's trying to find out if a wavelength of a laser at equal powers will have greater energy to pop balloons with.
Click to expand...

That's not what he said. He said:

I am trying to determine the optimal wavelength of laser that will pop a balloon in the least amount of time
Click to expand...

If you could somehow have identical beam profiles and powers, the absorption spectrum is no longer insignificant in determining which beam will penetrate first.
 
But, he further says:

laserstudent said:
My assumption is that at shorter distances, the blue laser will pop the balloons the fastest due to higher energy of its photons and the red laser will be the slowest. As the distance between the lasers and the balloons gets larger, the blue laser will take a longer time to pop the balloons due to its shorter penetration depth through the air and the red laser will take relatively shorter time to pop the balloons due to its relatively larger penetration depth. So at some time, the red laser will catch up to the blue laser as they both make their way popping through the line of balloons. For this particular experiment, I want to keep the wattage of the three lasers equal
Click to expand...

Are you suggesting that all things being equal, power, distance and beam profiles that this is a question that needs an answer?
 
I apologize for not introducing myself. This is my first time posting in a forum. I am a high-school sophomore, living in California. I am doing a science project for class and this is my first time working with lasers, so my knowledge is limited.

I understand the comments made by paul1598419, diachi, Blarg King, and Cyparagon, I am trying to experimentally determine what diachi has already stated.

“The energy of the individual photons does not matter, only the power matters, more specifically the power density. A red and a blue laser at the same power just emit different amounts of photons, the red emitting more. You can calculate the difference easily.
The distance will not make a difference, at the distances you'd need to see a difference you wouldn't be able to pop a balloon.
You need to take into account the beam specs, for this experiment to work each beam would need to have an identical divergence, geometry and power output. Assuming you'd see a difference in the first place. ”

I plan on keeping the power of the lasers, the beam profiles (power density), and the distances between the laser and the black balloon the same for all lasers. For my experiment, I am also assuming that the absorption spectrum of the black balloons are the same. Given that, I want to still experimentally see whether wavelength will affect the time it takes to pop the balloon.

I want to buy pre-assembled laser diodes with a lens, in a housing, with the driver attached. I am looking for three such assemblies: blue, green, and red. I want to find out what laser assemblies I can buy to carry out this experiment. Also, what should the wattage range be for the lasers to pop the balloons at a distance of around 2-5 meters?

Thank you for all your help!
 
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