High intensity line lasers at 355-1064nm see use in a number of modern production processes, including ablation, polymer welding and solar cell processing.
For applications such as these, laser intensities of more than 50mJ/cm2 at pulse durations of 10-20ns over a line of length 100mm or more are often required. Single mode lasers are unable to provide high enough pulse energies when spread over such long lines, while multi-mode lasers have higher intensities but cannot be focussed to a narrow enough line due to the high M2 value.
The solution is M2 transformation. Such M2 transformations are commonly achieved by micro-refractive methods (cylindrical lens arrays) or by fibre-optic methods. These methods are complicated, require multiple optical components and have many sensitive degrees of freedom that must be tuned within tight tolerances, and often tailored to the specific parameters of each costumer's laser system.
Laser Components alongside HOLO/OR offers the LeanLine system, a 2-module system that performs M2 transformation on a round input beam and converts it into a narrow line at focus. LeanLine uses an innovative diffractive approach to M2 transformation that reduces the number of elements required in the system and relaxes the required tolerances.
LeanLine takes an axis symmetrical, high M2 (multi-mode) beam, and outputs a lower M2 in one axis and higher M2 in the other. Subsequently, the axis with the high M2 is shaped into a line, and the low M2 axis is focussed into a narrow Gaussian profile. As the line is focussed using a cylindrical lens rather than a diffractive method, much narrower widths may be achieved, allowing the line intensity to reach high process thresholds
The two module system comprises of a first diffractive stage, used for M2 transformation and beam shaping, and a second refractive stage used for line length control and focussing in the narrow axis. This intuitive modular system provides great flexibility, allowing the same basic setup to be used to generate different line widths by simply switching the output module.
Diffractive solution advantages for solar cell processing:
- Easy alignment and installation;
- Extremely high precision for M2 transformation quality, achieved by the lithography production process;
- A fully transmissive (non-reflective), on-axis system;
- Aberration free;
- An be easily modified to produce different line lengths and widths;
- No internal focus points;
- Available in a wide spectral range from DUV to NIR.