We have developed high-precision machining based on high-power pulsed green lasers (30–40 ns pulse width) at multi-kHz repetition rate. Dynamics of material removal has been investigated using a copper vapor laser. We found that noticeable surface evaporation starts to appear as laser intensity exceeds 107 W/cm2. Material removal is then dominated by ablation at higher laser intensities. However, strong plasma absorption starts to appear as laser intensity exceeds 2 GW/cm2. This prolongs material heating by hot plasma via electron conduction, resulting in noticeable melt formation and expulsion. Maintaining laser radiance below the plasma-ignition threshold minimizes this melt formation. The optimum rate of ablation on metals was found to be ∼1 μm/pulse with a laser fluence of 50 J/cm2. Higher material removal rate can be achieved at higher fluence, but is mostly accompanied with unwanted melt formation and ejection. By keeping laser intensity within a few GW/cm2, we have demonstrated high-aspect-ratio machining with micron-scale accuracy and negligible heat affected zone. High-quality percussion drilling, trepanning, grooving, and slotting were demonstrated on metals and ceramics with a negligible heat affected zone. Straight holes with sizes varying from 500 to less than 25 μm were consistently drilled with a height-to-diameter ratio up to 40. The high quality machining with scalable machining speed promises expanded use of pulsed green lasers in micromachining.

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A growing appreciation has developed in the last several years for the copper vapor laser because of its utility in ablating difficult materials at high rates. Laser ablation at high rates shows promise for numerous industrial applications such as thin film deposition, precision hole drilling, and machining of ceramics and other refractories.

In a large-bore copper vapor laser (CVL), excessive gas heating at the axial region of the discharge lowers its efficiency by thermally populating the metastable lower laser levels. The associated lower gas density also lengthens the discharge field-diffusion time, leading to weaker axial pumping and undesired beam characteristics. Our laboratory has developed a novel approach to circumvent this obstacle by cooling the plasma radiatively via a series of segmented metal plates (septa) placed vertically along the length of the tube. This improved tube design significantly lowers the average gas temperature and shortens the radial delay. A 27% increase in laser power was observed with the addition of septa. We have characterized the beam intensity profile, spatial and temporal pulse variation, and beam polarization through extensive laboratory measurements. A detailed computational model of the laser has been used to characterize and interpret the laboratory results. Downloaded From: http://proceedings.spiedigitallibrary.org/ on 06/25/2016 Terms of Use: http://spiedigitallibrary.org/ss/TermsOfUse.aspx SPIE Vol. 2118 / 7 Downloaded From: http://proceedings.spiedigitallibrary.org/ on 06/25/2016 Terms of Use: http://spiedigitallibrary.org/ss/TermsOfUse.aspx