2.4 Development and Improvement of the Holographic Interference …
155
of the ways to solve this task is the simultaneous registration of the front edge shift
of the semiconductor crystal and the polished surface of the cooling vessel [57, 59].
The results obtained in such a way depend on the geometry of the diode fastening
and the degree of homogeneity of the temperature distribution in the cooling vessel
[60]. In this work, the methods for the study of the thermoelastic deformations of the
injection heterolasers are suggested. It is based on the control of two opposite edge
shifts of the semiconductor crystal.
Such an approach makes it possible to minimize the influence of the cooling
vessel and to expand the sphere of implementation of the holographic interferometry
method for studying thermal characteristics of laser diodes.
The optical scheme of the setup is presented in Fig. 2.47. The holographic microinterferometer has two object channels I and II where thermoelastic shifts of two edges
of the diode resonator are registered. With two totally reflecting mirrors 2–9, the
beam splitters 10–12 and the microlenses 13 and 14, the image of the resonator
edges is projected in the holography plane 19 onto two spatially separated areas,
which are located within the boundaries of the reference beam incidence area. The
latter is formed by the mirrors 8 and 9 and the lenses 16, 18. The hologram was
recorded on the plates PE-2. The plate was processed on the place of exposure. The
holographic image was recovered with the initial reference beam. In the area of the
resonator edge image, an interference pattern in infinite bandwidth was observed,
which corresponded to the superposition of the object wave recovered from the hologram and of the wave spreading from the diode in the moment of its excitation. The
interferogram illumination was measured in real time. The calculation of the shift
value in the point of the heterolaser facet along the direction of observation can be
found in the works [57, 62].
The scheme of fastening the laser diode on the copper cooling vessel and the
corresponding notations used during calculation of the temperature expansion of the
semiconductor crystal in the diode-cooling vessel system are shown in Fig. 2.47b.
The pump current transmission through the laser diode leads to heating and
thermal expansion of the semiconductor crystal as well as of the cooling vessel.
If the shifts of the two opposite edges are signed as x 1 and x 2 recorded in the
interferometer channels I and II, respectively, then
x 1 = δ 1 + x xl ; x 2 = δ 2 − x xl
(2.50)
where δ 1 , δ 2 are the inherent thermoelastic diode deformations; x cd is the diode
shifts as the whole along the observation axis by the expanding cooling vessel.
Thus, the full thermoelastic elongation of the semiconductor crystal is the
following:
l = δ 1 + δ 2 = x 1 + x 2 , ((x 1 > 0).
(2.51)
Designation x 2 is defined by the calibrated modification of the optical path
in object channel II. During calculation of l, the value compensation of thermal
expansion of the cooling vessel occurs in channels I and II. This makes it possible
155
of the ways to solve this task is the simultaneous registration of the front edge shift
of the semiconductor crystal and the polished surface of the cooling vessel [57, 59].
The results obtained in such a way depend on the geometry of the diode fastening
and the degree of homogeneity of the temperature distribution in the cooling vessel
[60]. In this work, the methods for the study of the thermoelastic deformations of the
injection heterolasers are suggested. It is based on the control of two opposite edge
shifts of the semiconductor crystal.
Such an approach makes it possible to minimize the influence of the cooling
vessel and to expand the sphere of implementation of the holographic interferometry
method for studying thermal characteristics of laser diodes.
The optical scheme of the setup is presented in Fig. 2.47. The holographic microinterferometer has two object channels I and II where thermoelastic shifts of two edges
of the diode resonator are registered. With two totally reflecting mirrors 2–9, the
beam splitters 10–12 and the microlenses 13 and 14, the image of the resonator
edges is projected in the holography plane 19 onto two spatially separated areas,
which are located within the boundaries of the reference beam incidence area. The
latter is formed by the mirrors 8 and 9 and the lenses 16, 18. The hologram was
recorded on the plates PE-2. The plate was processed on the place of exposure. The
holographic image was recovered with the initial reference beam. In the area of the
resonator edge image, an interference pattern in infinite bandwidth was observed,
which corresponded to the superposition of the object wave recovered from the hologram and of the wave spreading from the diode in the moment of its excitation. The
interferogram illumination was measured in real time. The calculation of the shift
value in the point of the heterolaser facet along the direction of observation can be
found in the works [57, 62].
The scheme of fastening the laser diode on the copper cooling vessel and the
corresponding notations used during calculation of the temperature expansion of the
semiconductor crystal in the diode-cooling vessel system are shown in Fig. 2.47b.
The pump current transmission through the laser diode leads to heating and
thermal expansion of the semiconductor crystal as well as of the cooling vessel.
If the shifts of the two opposite edges are signed as x 1 and x 2 recorded in the
interferometer channels I and II, respectively, then
x 1 = δ 1 + x xl ; x 2 = δ 2 − x xl
(2.50)
where δ 1 , δ 2 are the inherent thermoelastic diode deformations; x cd is the diode
shifts as the whole along the observation axis by the expanding cooling vessel.
Thus, the full thermoelastic elongation of the semiconductor crystal is the
following:
l = δ 1 + δ 2 = x 1 + x 2 , ((x 1 > 0).
(2.51)
Designation x 2 is defined by the calibrated modification of the optical path
in object channel II. During calculation of l, the value compensation of thermal
expansion of the cooling vessel occurs in channels I and II. This makes it possible