In order to estimate how inner bubbles will influence on optical
qualities of Ti-sapphire crystals, a nondestructive method based on
the utilization of an He/Ne laser emitting at 633 nm. A focused
beam from the laser was sent through the wafers (diameter 30 mm, thickness 5 mm) cut from Ti-sapphire crystal grown with
pulling rate 4 mm/h and rotation rate 8 rpm. The output intensity
was recorded with a CCD digital camera connected to a computer.
For the measurement of the region exempt of defects such as bubbles
or cracks etc., the transmitted laser beam presented a near
Gaussian profile (Fig. 14b) demonstrated high optical grade. When
the laser beam was focused on the area contains intrinsic small
bubbles, Fig. 14c visualized more strongly losses in intensity as
well as significantly disturbed profile. Fig. 15 shows wavefronts
recorded using 5 mm thickness and 30 mm diameter wafers cut
from Ti-sapphire crystal grown under stationary regime
(V = 4 mm/h, rotation rate 8 rpm). A focused beam from He–Ne
laser was sent through the wafer. The diameter of the laser waist
without sample was measured to be 140 lm. A focal imaging system
was used to image the end face of the sample into the beam
analyzer Beamwave 500 from Phaseview. The analyzer recorded
the beam and the wavefront profiles. The Getlase software was
used to analyze the beam profile and to calculate the coefficients
of the wavefront decomposition using Zernike polynomials. The
wavefront profile measured without sample was perfectly plane
(Fig. 15a, RMS = 10 nm). Fig. 15b illustrates the wavefront profile
for the laser beam propagation in the bubbles. The wavefront profile
is modified intensely by the defects (RMS = 127 nm). A Zernike
decomposition of the wavefront profile allows quantifying optical
aberrations observed after laser propagation in the region contains
bubbles. The bubbles cause significant astigmatism, coma and trefoil
aberrations of the histograms featuring pertinent terms in the
Zernike decomposition (Fig. 15c). The laser beam and wavefront
measurements bring out and permit to quantify how bubble
defects decrease seriously the optical properties of Ti-sapphire,
so all ways and means should be utilized to avoid this defect in
the interest of high optical quality of crystals.