Keiu Tokumura

Laser ablative shaping of plastic optical components for phase control

A new scheme for phase control of optical components with laser ablation has been developed. One can ablate the surface shape of optical plastic material coated on a glass plate by using 193-nm laser light to control the transmission wave front. The surface shape is monitored in situ and corrected to attain the desired aberration level. The irradiation fluence is approximately 40 mJ/cm(2), and the ablation depth/pulse is approximately 0.01 microm/pulse for UV-cured resin. A wave-front aberration of 3.0 lambda is reduced to 0.17 lambda for flat surface shaping. For spherical surface generation, an aberration of 2.5 lambda is reduced to 0.2 lambda. The increase in surface roughness is kept within acceptable levels.

Laser ablative shaping of collimator lens for single mode fiber

A new scheme for the phase control of optical elements using laser ablative shaping (LAS) has been developed. An ArF excimer laser was used as the light source. This method was first demonstrated with glass-plastic hybrid plates of diameter of 5 cm on a interferometer. The wavefront aberration of transmitted light was improved from 3 /spl lambda/ to /spl lambda//5 which is good enough for general purpose of optics. This LAS scheme was applied to the fabrication of micro-lens for the collimation of laser diode (LD) and single mode fiber (SMF). In these cases, the output laser beam from LD or SMF was collimated by micro-lens, and the wavefront distortion of output beam were measured by a Shack Hartmann wavefront sensor due to large wavefront aberration. The wavefront aberration of output beam from the collimation lens formed on the output surface of SMF was corrected from 15 /spl lambda/ to 2 /spl lambda/ which is very close to the actual application for the connection of SMF.

UV laser ablative figuring of precise optics

The new method of surface shaping for optical plastics have been investigated using UV laser ablation on acrylic resin (PMMA) or ultraviolet (UV)-cured-resin. The surface figuring of optical flat was obtained with direct beam irradiated ablation with ArF laser. The depth of the figuring was determined with the measurement of wave front distortion on the optics using interferogram. The ablated surface had small surface roughness. The miniature size optics such as the collimate lens for a diode laser (LD) was fabricated on flat PMMA at using the focusing beam irradiation. The wave front of LD light through the LD lens was measured with Shach-Hartmann sensor. The wave front control for LD light was carried out with the measured wave front data by the laser ablation on the LD lens surface. The collimated LD light has been obtained.

Laser ablation process of quartz material using F2 laser

An investigation on the laser ablative shaping (LAS) of the quartz glass has been made experimentally. F2 laser was used as the laser light source for efficient ablation of quartz material. The output beam of F2 laser was focused on to the surface of quartz plate. The ablation rate was about 10 micron m/pulse at the irradiation fluence of 2 J/cm2. A uniform ablation of quartz plate has been demonstrated using F2 laser. The waveform of incident and transmitted laser light was measured by high speed photo-tubes to observe the time dependence of the absorption. The measured waveform indicates that the absorption was small at the leading edge of the laser pulse, and a strong absorption was induced at the end of laser pulse due to the excited state absorption. These phenomena are quite similar to both in F2 and ArF laser light. We have developed a simple model in which the instantaneous absorption is proportional to the absorbed energy prior to the moment. The calculated absorption was in good agreement with the measured wave- form. The change of transmittance in UV and VUV region was measured after the irradiation of F2 laser for samples of different concentrations of impurities.

Laser ablative figuring of optical elements for phase control

A new scheme for the control of the phase of the optical component using laser ablation has been developed. The surface shape of optical plastic coated on a glass plate is ablated using 193 nm laser light to control the transmission wave front. The surface shape is monitored fluence is about 45 mJ/cm2, and the ablation depth per pulse is about 0.01 micrometers per pulse. Flat and spherical surfaces are generated using this method to reach the wave front distortion of 0.2 (lambda) . Micro-lenses for the control of the beam profile of the laser diode has been tried.

F2 laser ablation process of silica glass

The laser ablative figuring of the silica glass has been investigated experimentally. F2 laser and ArF excimer lasers are used as the laser light source for efficient ablation of silica glass material. The output beam of F2 and ArF laser were focused on to the surface of silica glass plate. The ablation rate were measured by a surface profilometer. The process on the surface was done by scanning in X-Y direction and a uniform ablation was observed. However the surface roughness was large as compared with the case of PMMA. The waveform of incident and transmitted laser light was measured by high speed photo-tubes to observe the time dependence of the absorption. The measured waveform indicates that the absorption was small at the leading edge of the laser pulse, and a strong ablation was induced at the latter part of laser pulse due to the excited state absorption. These phenomena are quite similar to both in F2 and ArF laser light. We have developed a simple model in which the instantaneous absorption is defined by the absorbed energy prior to the moment.

UV laser ablative shaping of optical surface using ArF laser

A new scheme for phase control of optical components using laser ablation shaping (LAS) has been developed. The surface shape of optical plastic material coated on a glass plate is ablated using 193 nm laser light to control the transmission wave front. The surface shape is monitored in situ and corrected to attain the desired aberration level. The irradiation fluence is about 40 mJ/cm2, and the ablation depth per pulse is about 0.01 micrometers per pulse for UV-cured resin. A wave front aberration of 3.0(lambda) is reduced to 0.17(lambda) in the case of flat surface shaping. In the case of spherical surface generation, an aberration of 2.5(lambda) is reduced to 0.2(lambda) . Increase in surface roughness is kept within the acceptable levels. This scheme has been applied to the fabrication of micro-optical elements for the collimation of laser diode (LD) or single mode optical fiber (SMF). In the case of LD lens, micro- collimate lens was placed at the output surface of LD, and the wave-front error was measured with Shack Hrtmass wave- front sensor. In the case of SMF, small lens was formed directly at the output surface with UV-cured resin. The laser beam was focused to 250 micrometers in radius for micro- fabrication. The wave-front distortion was decreased from about 15(lambda) to less than 2(lambda) in mm size lens.

Wavefront control of optical components by laser-ablative figuring

A new method for figuring the surface profile of optical plastics and optical glass have been proposed and demonstrated. An ArF excimer laser is used to ablate very thin layer of the surface of the substrates. The shape of the ablated surface is monitored by an interferometer in site condition. The ablation rate of PMMA is 0.08 micrometers per pulse at the energy density of 50 mJ/cm2. The optical glass (BK-7) can be ablated 0.15 micrometers per pulse at the fluence of 1.5 J/cm2.