We used a commercially available 75 MHz regeneratively amplified laser system emitting 50 femtosecond pulses of
energies up to 3nJ at a wavelength of 800 nm. All waveguides were fabricated by focussing the femotsecond pulse train
polarised parallel to the x-axis to a distance of approximately 125 μm below the sample surface using a 0.65 NA, ×40
microscope objective and translating the sample along the y axis. To find the optimum waveguide fabrication parameters
the translation speed was varied from 2 to 100 μm/s. We introduces a method of measuring the refractive index of
optical waveguide in ten micrometer. Useing CCD to measure the two-dimensional near-field light intensity distribution
of the output cross-section of the waveguide, by measuring the two-dimensional near-field light intensity distribution of
the output cross-section of the waveguide can be calculated the two-dimensional distribution of refractive index of
waveguides. The context detailedly gives measurement results about femtosecond laser inducing the near-field intensity
of lithium niobate optical waveguide cross-section and calculations of refractive index of optical waveguide. The results
show that the refractive index of waveguides showed a large central, gradually reduce and the change of refractive index
in the range of 0.001. This method is of great significance to measure the optical waveguide refractive index
distribution.
In recent years, the microfabrication of Lithium Niobate (LiNbO3) based optical integrated devices by using femtosecond laser pulses has been attracting increasing attention. One key current challenge is to understand the mechanism of the interaction of femtosecond laser pulses on LiNbO3 crystal, which is still elusive. Here we demonstrate the etching of LiNbO3 crystal surface by using tightly focused femtosecond laser pulses with repetition rate 75 MHz, pulse duration 50 fs, and single pulse energy 3nJ. The morphology of the etched area is observed by a scanning electron microscope (SEM) which shows the laser illuminated area has obvious thermal damage. When the etching time is 30 seconds and the etched area is 42μm in diameter, thermal damage is observed within the area with 28μm diameter, redeposition is observed in between 28-34μm diameter, and modification is observed in between 34-42μm diameter. A theoretical thermal diffusion model is built to simulate the temperature distribution in the area etched by laser pulses with repetition rates 1 kHz, 1 MHz, and 75 MHz, respectively. The simulation result from 75 MHz repetition rate matches experimental observation very well. The results show that there is thermal damage when LiNbO3 crystal is illuminated with high repetition rate femtosecond laser pulses.
Access to the requested content is limited to institutions that have purchased or subscribe to SPIE eBooks.
You are receiving this notice because your organization may not have SPIE eBooks access.*
*Shibboleth/Open Athens users─please
sign in
to access your institution's subscriptions.
To obtain this item, you may purchase the complete book in print or electronic format on
SPIE.org.
INSTITUTIONAL Select your institution to access the SPIE Digital Library.
PERSONAL Sign in with your SPIE account to access your personal subscriptions or to use specific features such as save to my library, sign up for alerts, save searches, etc.