In general, you will need an extractor that has three stages of filtration:
1) A high-efficiency prefilter with a rating of at least F8 or F9 to protect and prolong the life the critical HEPA filter.
2) A true HEPA filter with at least a rating of 99.997% efficiency at 0.3 micron to filter out submicronic particles generated by laser processing.
3) A high-capacity activated carbon filter with at least 20 pounds of carbon. The more, the better. Make sure each filter can be replaced independently, which reduces waste and cost. Automatic flow compensation is also an important feature to maintain a consistent extraction flow even as the filters begin the block. Responsive customer support and the ease of serviceability are probably the most important requirements to consider as they will limit potential downtime.