OFR High NA Long Working Distance Focusing Objectives are designed for materials processing using ultrafast lasers. OFR HNA-LWD Focusing Objectives combine two essential features without coverglass: high numerical aperture and long working distance. The high peak power at the focus of an ultrafast laser pulse causes non linear multiple photon absorption. With power above threshold, molecular bonds are broken and material is ablated. Because the ultrafast pulse interacts with the sample on a pico-second or sub-picosecond time scale, faster than the characteristic time for heat diffusion, any thermal damage that is experienced with long-pulsed lasers is avoided.
Smaller than diffraction-limited features can be directly written on a surface. Even though the focal spot is diffraction limited, if the power density in the peak of the Gaussian spot is above the threshold for ionization, then material which interacts with only the most-intense sections of the focal volume will be cold ablated. The dimension of the ablated feature can be smaller than the Airy's disc. Thus, this method enables cutting, drilling, writing and hole-shaping with dimensions smaller than possible with other types of lasers.
The long working distance allows
a current of dry nitrogen to blow away
plume and debris from the ablation.
OFR HNA-LWD Focusing
Objectives consist of air-spaced
components, with no cemented
interfaces to limit usable laser
power. All surfaces are AR coated.
The mounting cell is equipped with
the universal standard Royal
Microscopical Society (RMS) thread
(Whitworth 0.8" x 36 TPI).
Further, OFR HNA-LWD Focusing
Objectives are designed for no
Expanded input beam into the
Focusing Objective is required, 10
mm diameter. Generally, any high
quality beam expander should be
sufficient to expand the incident
laser beam. See, for example, page
OC-10, Laser Beam Expanders.