Is it possible that a low energy laser could be more effective than a higher energy one on the surface of a certain material?(e.g. Titanium). For example the low energy one can microstructurally melt the surface of the sample, but the high energy one cannot.
Is it possible that depending on the targeting materials structure or compound, the response of laser changes?
Is there any reference regarding these subjects?
Yes it is possible. It depends on the medium on which the laser beam propagates. Each medium can bear a certain density of power. If this density of power is exceeded, the medium is ionised in a plasma, this is called the "breakdown". In air, the maximal density of power before breadown is about 4 GW/cm². Below, there is a partial breadown. When the plasma appears, it block the coming photons and there is nore more energy deposited in the material. The plasma can even reflect the photons in the laser source and it is a possible crash for the laser. In water, the breakdown threeshold is about 8-9 GW/cm². See :
A. Sollier, L. Berthe, and R. Fabbro, Eur. Phys. J. AP 16, 131-139 (2001).
regards
This really depends strongly on many parameters: energy (related to wavelength), power, power density, and materials engineering concerns all affect the choice of laser wavelength and power.
There are two meanings of "high energy": UV lasers are higher energy because they are shorter wavelength. IR lasers are low energy because they are longer wavelength. Certain materials respond differently to wavelength. The other meaning, of course, is whether the laser brings low power or high power to the target.
Generally, high-power lasers are more capable of cutting through certain materials, and UV lasers are preferred for laser etching systems because they can be focused to a finer spot and generally bring more power for the same cost. Cutting metals requires more energy density in order to achieve the cut before the heat produced is conducted away, for instance. However, some materials are highly reflective at UV wavelengths making them easier to cut at other wavelengths which are absorbed.
Additionally, there can be human factors involved. From personal experience, I can tell you that reflected 1560um laser radiation is uncomfortable, but 2um radiation burns. While all radiation from laser machining should be stopped before human exposure, reflective (even diffuse) surfaces can make this difficult in an industrial situation.
Heat-hardening and other surface-only treatments require wavelengths that do not penetrate the target material and power levels that affect the structure without ablating. Additionally, the material removed by ablation doesn't merely cease to exist, and can condense on nearby surfaces, especially bad when laser-machining plastics. Thus, not only laser power and wavelength have to be considered, but ablated-material removal, cooling of the worked piece, and other potential aspects must be considered.
In dermatology, now a very large share of the laser surface-processing market, laser power and wavelength must be well-controlled to obtain the desired results without causing deep-tissue affects or other side effects. Here, a more-powerful-laser is decidedly a bad thing!
As for references, I can't point to any, but you may find considerable resources in your institution's Materials Engineering and Medical departments.
It depends on the wavelenght of the laser also. Into vacuum the UV is more efficient than the IR. It depend also on the absoption of the laser radiation by the target and so on the physical properties of the target. I can suggest to you my articles on Ti and Nd:YAG laser tripled on frequency.
Any laser induced processes in material are dependent on the parameters of the laser and the properties of the material, particularly the thermal properties.
Absorption of a laser in any material is dependent on the wavelength of laser. Breakdown of material takes place after certain intensity of laser. Once the breakdown occurs the behavior of laser changes. All these processes involves the properties of laser and its parameters as well as on the thermal properties of materials.
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