Dear Dmitry,

Check this out:

http://www.ipgphotonics.com/en/products/lasers/high-power-cw-fiber-lasers/1-micron/yls-cut-1-15-kw

Please wear laser safety glasses!! :)

Kin

Here are a few more:

1070 nm

https://www.coherent.com/lasers/laser/diode-laser-systems-and-fiber-lasers/highlight-fl-series

https://www.coherent.com/lasers/laser/diode-laser-systems-and-fiber-lasers/h-lase

https://www.coherent.com/lasers/laser/diode-laser-systems-and-fiber-lasers/o-lase

10.6 um CO2 laser

https://www.coherent.com/lasers/laser/co2-and-co-lasers/ch-series-high-power-lasers

https://www.coherent.com/lasers/laser/co2-and-co-lasers/fh-series-high-power-lasers

I am not endorsing these lasers. Just showing examples that may meet your needs.

Kin

Dear Kin,

Many thanks for the links!

Power and wavelength of these lasers are OK. However, as far as I understand, all these lasers have the beam diameter less than 1 mm, while we need the beam diameter of around 10 mm.

I don't know if easy solutions exist allowing to increase the beam diameter up to ~10 mm?

Would a CO2 laser with a beam expander (collimator) work?

Hello,

Take a look at http://www.prclaser.com/products.html

Igor

Dmitry,

You can indeed use a beam expander to increase your beam diameter to accommodate your application. There are a few potential parameters to consider:

(1) choice of wavelengths

(2) laser beam profile

(3) optics

(4) beam shape

(1) Near IR and Far IR (CO, CO2) lasers have different reflectivity on copper, so you may have to estimate how much of an incidence irradiance (W/cm2) is actually converted to heat on the copper before choosing your laser.

(2) The laser beam profile from the sources I pointed out are pretty good, in which the M-square values are very small and close to 1. This means the output beam is very close to Gaussian. Even if you expanded the beam with an expander to the diameter that you wanted (Gaussian beam diameter is defined at the 1/e^2 waist from peak power), the incident beam at your copper surface is not uniform. You may need to consider using a diffractive optical element (DOE) that converts a Gaussian beam to a tophat beam. This is easier for a NIR laser, but problematic for a Far IR (e.g. CO2) laser. You can find DOE from some vendors for VIS-NIR but you will need to know the threshold damage irradiance for those DOE's.

http://www.holoor.co.il/Diffractive_Optics_Products/Diffractive_Beam_Shapers/BeamShaper_home.htm

https://www.lasercomponents.com/us/product/diffractive-optical-elements-for-beam-shaping/

https://www.luminitco.com/products/light-shaping-diffusers

https://holographix.com/optical-diffusers.html?gclid=EAIaIQobChMIzeTZmvja2gIVCcNkCh1dxQQAEAAYAyAAEgLiQvD_BwE

https://www.rpcphotonics.com/engineered-diffusers-information/

(Again, I am not endorsing these companies. They may or may not work for your application)

Typical optics for UV-VIS-NIR are not useful for Far IR wavelengths and you are unlikely to find many who makes DOE for the CO2 laser. Which now brings us to the next point....

(3) The optics for the beam expander for the CO2 laser are more exotic. You will need to use Zinc Selenide, Germanium, Si, or GaAs, for example. They are more expensive and harder to handle/maintain.

(4) If you do not want a circular beam, you can again reshape your beam geometry from circular to square with a DOE, but could again run into the same issue with availability and threshold damage irradiance.

Kin

Dear friends,

Many thanks for your replies.

Dear Kin,

I'm really surprised about such a variety of existing DOEs for lasers. Theoretically, they can fully suit our needs (to have uniform laser beam 10 mm in size).

Still a couple of concerns remain:

1) Threshold damage irradiance. I doubt that existing DOEs can easily cope with the beam power of 5 kW. Even 1% of the light adsorption in the optical element will result in 50 W of heat generation in the optical element.

2) Power adjustment. In our experiments we need to gradually adjust power from 0 to the maximum value (5 kW). Is it possible with the existing lasers pointed out above?

You are correct that most DOE's in the market are unlikely to withstand 5 kW, more specifically 5 kW/cm2. This is especially true for DOE technologies based on resin and polymer/plastic materials. DOE made from etching process of glass materials may have a better chance of surviving high irradiances. Even then you will have to keep the surface very clean. You should call the individual vendors to ask for specs.

Yes, most systems should have controller electronics built in with software driver through which you can interface with from their proprietary UI, or write you own code based on your applications. However, with such high power laser systems, you will likely have a high lasing threshold current, where, for example, the lowest power you may get to is, say 100W, for a system spec-ed at 500W to 5kW. That is because the laser will only start lasing at a defined threshold current, and may operate outside of its linear region - so you need to calibrate yourself. Any light you may measure below the lasing threshold is just spontaneous emission and broadband.

In general, it is good practice to split a tiny fraction (e.g. 1%) of the laser beam off to a reference monitor/detector so that you know if your output power is consistent, drifting, or exhibiting hysteresis (when you go from high to low power vs. low to high power).

Kin

Dear Dmitry, diode laser stack may be a choice. A single stardand diode laser bar is 10mm wide and could provide 150W cw output at 976nm, more bars stacked, more power you get. The collimated output of the stack is polarized (so you can combine two stacks output with polarization prism), and is a natural 10mm wide rectangular beam (another side depends on number of bars you needed, the pitch between bars is around 1.5mm). With cylindrical lens combination, you could easily get 10mmX10mm beam on the copper plate. It's cheap, robust, and the power could easily adjusted by driven current.

Dear Kin,

Power range from 500 to 5 kW might be OK.

I think the range from 0 to 500 W can be covered using laser attenuator of some kind.

Dear Dmitry,

You can definitely use an ND filter or a splitter to get to the lower range depending on your system design, but you should have two sets of calibration curves.

Am curious what your results will show. Are you going to use thermal imaging to monitor heat transfer to and from the copper plate? It is a bit tricky to use a thermal camera to monitor a metallic surface because of the emissivity. But please do share.

Kin

Dear Hongyan,

Many thanks for your advice. We will try it.

Dear Kin,

For measurement of the substrate surface temperature and for determination of the local heat flux across the copper plate, we are going to use 2 thermocoples embedded in the plate.

OK, I will keep this thread updated with our progress.

dear Dmitry, I am afraid there is an issue more, that apparently was not considered in this thread. Every high-power laser has a spatial profile of the intensity which is highly irregular and fluctuating. As a consequence, your target will be hit by a number of photons/time/area which changes locally and produce a non uniform irradiation/heating. The M2 parameters given by laser companies does not give any information about the intensity uniformity of the laser beam, and by an apparent paradox, it may happen that the better the M2, the less uniform is the laser beam shape.

As a consequence, I recommend the use of a homogenizer made by cylindrical mirrors (transmitting optics is not suitable for kW-range lasers). Googling "Laser beam homogenizer for high power lasers" you will find what you need.

Hope this may help

Paolo

Дмитрий!

Может рассмотреть вопрос нагрева не только лазером?

Ваш удельный тепловой поток не такой большой.

На мой взгляд, несравненно проще его реализовать ИК нагревом.

Dear Paolo,

Many thinks for this valuable info. I'll google it.

Михайло,

Тепловой поток довольно приличный. На поверхности Солнца поток около 6 кВт/см2.

Что Вы подразумеваете под "ИК нагревом", можно поподробнее?

Дмитрий!

Посмотрите в книге "Электротермическое оборудование. Справочник" соответствующий раздел.

Например в:

http://mirknig.su/knigi/apparatura/85066-elektrotermicheskoe-oborudovanie-spravochnik.html

ОК, спасибо!

Why do you need laser just for heating the small stamp sized copper plate..anyway most of the power will be reflected (unless the surface is black)..what you are t=discussing happens quite often at the anode in some high power electron tube (e.g. X-ray tube with water cooled anode or collector).I air you may consider using a powerful plasms discharge (like witha welding equitment..

Dear Fritz Caspers,

Other possible solutions are discussed in the following thread:

https://www.researchgate.net/post/Can_anyone_suggest_an_engineering_solution_to_generate_a_very_high_heat_flux_at_the_surface_area_of_around_1_cm2_3-5_kW_cm2

Why it should be laser? I saw aluminium slab of ~100 x 150 x 10 mm3 sizes that was bendeded by 7 mm by light of impulse lamp ~10 usec. duration. Change of discharge capacitor tension gives control of power, temperature, etc.

Dear Valeriy Sterligov,

Thanks for your reply. What kind of lamp is it?

It was Pulse Forge 3200 of novacentrix.com

It was Pulse Forge 3200 of novacentrix dot com

It was Pulse Forge 3200 of Novacentrix

Sorry for repeating previous message. I have received message of an error and try to change the text, but I didn't see that my messages already appeared.

Got it, thanks!