Q1. Answer all parts-
(a) Briefly describe the principal components of a laser-based manufacturing work cell. Give examples of each key component for a specific application.
(b) Estimate the peak fluence for a pulsed laser, with a Gaussian beam profile, emitting an average power of 1.2 W, at a repetition rate of 100 kHz, when focused to a spot diameter of 50 microns. Estimate the diameter of the ablated crater if the threshold of ablation for tissue positioned at the focal point is 1 J cm-2.
(c) The temporal brevity of a laser pulse is a unique feature of laser technology. Describe the temporal sequence of the different physical interactions which are known to occur during the ablation of a metal using a fem to second laser pulse.
(d) Explain the concepts of maximum permissible exposure and nominal optical hazard distance in laser safety. Estimate a nominal optical hazard distance for a CO2 laser (MPE =1000 Wm-2) for a beam of 3 mm diameter, 1milli-radian divergence, when the beam of 100W is focused by a 25 mm convex lens, positioned at 4 m from the laser aperture.
Q2. Answer all parts.
(a) Using a diagram, or otherwise, compare and contrast the spatial and spectral emission profiles from four different artificial sources of light.
(b) Explain in as much detail as you can, the principle of operation of a laser. Give examples for how each concept you describe is implemented practically, by considering a specific laser source used for a medical treatment or medical device manufacturing.
(c) Estimate the depth of focus for an optical system when a laser beam, M2 = 1.2, wavelength, λ = 515 nm, and the diameter, d = 5 mm, is incident on a convex lens of focal length 25 mm. Describe in practical terms what this depth of focus means.
Q3. Answer all parts.
(a) Derive an energy balance equation for how the optical energy delivered to a thin material of thickness, t, density, ρ, is accounted in a laser cutting process at a velocity, v, when the laser spot diameter is given by w.
(b) Describe in practical terms, the dependence of the following key parameters when a pulsed laser is used to produce a linear cut in a material by vaporisation; (1) the diameter of the laser spot, (2) the velocity of the cutting process, and (3) the thickness of the material to be cut.
(c) Estimate the maximum scan speed obtainable to produce an overlap of 60% when a pulsed laser, operating at a repetition rate of 100kHz has a focused beam diameter of 20 microns.
