Optical machining with IMRA μ Jewel

1. Optical machining with IMRA μJewel Sanghyun Lee / Prof. Alan Hunt / Prof. E.F. Hasselbrink

2. • • • • •Contents • Performance measurement • Newly observed phenomena • Effect of glass geometry – resonance effect • Effect of laser chopping • General tendency of optical machining

3. 1-1.Performance measurement Long channel machining • Channel Length: 300µm • Machining time: 90min • Pulse energy: 27nJ • P.R.R.: 100kHz Due to the “football” shaped focus, the cross-section of the channel is not uniform. IMRA μJewel shows very good performance of long channel machining contrary to the previous model having 200kHz PRR. Optical machining with IMRA μJewel

4. 1-2.Performance measurement nCE channel machining • Channel Length: 850µm • Machining time: 250min • Pulse energy: 27nJ • P.R.R.: 100kHz Black spots are dirt mixed with debris in surrounding water. IMRA μJewel also showed very good performance of nCE device machining. Optical machining with IMRA μJewel

5. 2-1. Newly observed phenomena Induced bubbles on/above the surface * Pulse energy: 27nJ, PRR: 100kHz Bubbles are induced on/above the glass surface during the machining with 27nJ pulse energy. It is not because of the penetration holes. Surface vibration or secondary focus can explain it. Optical machining with IMRA μJewel

6. 2-2. Newly observed phenomena Bubble entrapment at the focus Surprisingly bubbles extruded from the central hole are strongly attracted to the focus, being trapped at the focus. And it is released, when the bubble has enough buoyancy force. * Pulse energy: 23nJ, PRR: 100kHz The reason of strong attraction and entrapment is not clear. a. The surface vibration by the laser pulsation can explain the attracting and trapping of bubbles b. The circulation of water due to the local heating by laser focus can explain the attraction. Optical machining with IMRA μJewel

7. 3-1. Effect of glass geometry – resonance effect Machining with different glass substrate Machining with different cover slips having different geometry (different natural frequency) were tested to see the resonance effect. Normal glass substrate 25x25mm, 170um thickness cover slip Modified glass substrate Normal cover slip glued with cylindrical reservoir containing water Optical machining with IMRA μJewel

8. 3-2. Effect of glass geometry – resonance effect Machining with different glass substrate * Pulse energy: 23nJ, PRR: 100kHz b. Modified glass substrate a. Normal glass substrate Optical machining with IMRA μJewel

9. 3-3. Effect of glass geometry – resonance effect Machining with different glass substrate The modified cover slip shows a little bit better performance (6.78 μm) than the normal cover slip (5.88 μm). This shows that the surface vibration affect the machining, which is one of the most possible explanations about the performance increase of μJewel, the bubble entrapment and induced bubbles on/above surface. Optical machining with IMRA μJewel

10. 4-1. Effect of laser chopping Machining with laser chopping 100Hz 200Hz 400Hz 800Hz Optical machining with IMRA μJewel

11. 4-2. Effect of laser chopping Machining with laser chopping • Machining performance is affected by the laser chopping and the feed rate. • 800Hz chopping shows best performance. The advantage of chopping is bigger at the slow feed rate region. In high feed rate region, only 800Hz chopping shows clear difference. Optical machining with IMRA μJewel

12. Machining with laser chopping 4-2. Effect of laser chopping • Although laser chopping decreases the average power input to an half, the machining performance increased up to double. • The chopping can increase the water supply to the focus area, and the pressure field inside channel can be retuned as the chopping frequency. Optical machining with IMRA μJewel

13. 5-1. General tendency of optical machining Machining with various feed rate μ-Jewel also shows general tendency related to the feed rate. Slow feed rate can make longer channel in single scanning of laser. However, slow feed rate means longer machining time. Feed rate is also related to the surface roughness. Optimal feed rate can be decided by these two factors. Optical machining with IMRA μJewel

14. Appendix Machining pattern for long channel x N dA A Us t tb Generally, Us and dA should be decreased while A andN should be increased during machining for long channel. Fluency of laser focus, transfer media, type of glass, and geometry of channel affect these factors. In order to increase the length, time needs exponentially. Optical machining with IMRA μJewel

15. Machining at the different conditions • Difference in natural frequency: • The natural frequency of normal cover slip is about 1kHz. The custom built reservoir on the normal cover slip would change the natural frequency of it very much. Because the natural frequency of custom cover slip is closer to the laser PRR, it is advantageous in ultrasonic wave agitation. • 2. The significant differences would have happened with the previous μJewel having 200kHz. With 200kHz PRR it is much more difficult to generate vigorous ultrasonic wave agitation for better debris extrusion. Practically ultrasonic cleaning bath is operated under from 20 to 40kHz wave agitation due to the best performance in generating cavitation bubbles. Optical machining with IMRA μJewel

16. What caused the differences? 1.Ultrasonic wave agitation: 20 ~ 100kHz is practically used frequency band for ultrasonic excitation such as an ultrasonic cleaning bath. As the frequency goes up, the cavitation bubbles due to the ultrasonic agitation is difficult to generate. 2.Advantages in acoustic feature: Low PRR is thought to be advantageous in acoustic features of optical machining such as pressure node formation. Therefore the difference in PRR (200kHz & 100kHz) can affect the long channel machining performance. Optical machining with IMRA μJewel