Optical System Design Issues

As you plan a part machining project that involves UV excimer lasers, use the following as a guide in determining how best to achieve the results you require using the correct optical system.

Determine power density required

• Which available wavelength is best?
• What is the ablation threshold of the material?
• Experiment to determine optimum fluence (lowest is best).

Determine required exposure area

• What are the required feature sizes?
• Can you break the feature into smaller portions?

Determine resolution and optical system type

• Determine whether to use a contact mask or imaging system (LWD or microscope system).
• Determine which objective is best.
• Select an objective that minimizes optics losses.

Determine pulse energy required

• Required pulse energy on-target = (required fluence x feature area).
• Don’t forget to factor in optics losses.

Determine optical parameters

• Select a demagnification.
• Maximize BUF using beam shaping/splitting as required.
• Determine optical path using readily available optics.
• Consider size of beam delivery system and support structure.
• Determine if is beam uniformity is critical and whether to use a homogenizer.
• Consider optics losses.

Select laser and illumination scheme

• Laser energy required = (required pulse energy on-target x BUF).
• Select the lowest pulse energy laser to do the job.
• Determine if pulse energy required is greater than maximum output of available lasers.
• Reconsider optics scheme to reduce losses.
• Consider scanned illumination techniques.

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