1. Field of the Invention
The present invention relates to a laser microscope and, in particular, to a transmission type confocal laser microscope which forms an image of a transmitted light from a specimen.
2. Description of the Related Art
Confocal laser microscopes generally scan a laser light spot which is focused to a size of about 1 micron along a specimen. A light having a brightness or darkness in individual positions (points) is detected by a photoelectric transducing sensor. A converted electric signal is integrated for displaying it on a large screen of a monitor display. This type of confocal laser microscope has an advantage in that defocussed light or spurious light can be eliminated since the specimen is always illuminated in only individual desired positions so that unnecessary spurious light is not mixed with a desired light and since light is received through a pinhole having a size which is substantially equal to that of the specimen scanning spot light in a position which is in a conjugate position for specimen plane. Accordingly, confocal laser microscopes provide a higher resolution and contrast in comparison with conventional optical microscopes even if the same objective lens is used.
Confocal laser microscopes are classified into two types, i.e., a reflection type laser microscope in which light reflected from a specimen is imaged and a transmission type laser microscope in which light transmitted through a specimen is imaged. A typical structure of the conventional transmission type confocal laser microscope is schematically shown in FIG. 2. This type of laser microscope emits a polarized laser light from a light source 1. The flux of the light is enlarged by an expander 2 and is transmitted through a polarized beam splitter 3 and is scanned in a transverse (X) direction and in a vertical (Y) direction by means of Galvano-mirrors 4 and 5 which are Galvanometers with mirrors. The light is once converged by a relay lens 8 in a position of a field stop 7 (corresponding to an imaging point of an objective lens). The light is transmitted through an illumination side objective lens B and is scanned on and along a specimen 9 as a spot.
The laser light which has been transmitted through the specimen 9 is transmitted through a transmission side objective lens 10 which is optically equivalent to the illumination side objective lens 8 and is imaged on the surface of a concave mirror 11. The concave mirror 11 has a reflective mirror surface which is spherical around the pupil position of the transmission side objective lens 10. The light flux which is reflected on the mirror 11 is returned via the same optical path. A 1/4.lambda. wave length plate 12 which changes the polarization direction by 45.degree. is provided between the concave mirror 11 and the transmission side objective lens 10. The reflected laser light is incident upon the above mentioned polarized beam splitter 3. Only the light which was transmitted twice through the 1/4.lambda. wave length plate 12 is reflected and is bent in a normal direction by the splitter 3. The split and bent light is transmitted through a condenser lens 13 and a pin-hole 14 is incident upon a specimen signal detecting sensor 15 comprising light receiving elements. The detected signal is photoelectrically converged into an electric signal and is then fed to a memory.
In the drawings, reference numeral 16 denotes a binocular head; 17 an optical path switch which is used when the binocular head is used; 18 a light source for vertical overhead illumination; and 19 a relay lens for the light source
In order to use the conventional type confocal laser microscope, a preparation 21 is firstly placed on a specimen stage 20 as shown in FIG. 3. Light is focussed on the surface of the specimen 9 by the illumination side objective lens 8. It is necessary to shift or displace the transmission side objective lens 10 by a slight length (L) each time when the transmission side objective lens 10 is adjusted since the level of the specimen is different depending upon the thickness of the preparation 21. The thickness of the glass portion of the preparation usually has variations within about .+-.0.3 mm among the different preparations.
Accordingly, the optical path changer 17 is conventionally switched to move toward an optical microscope unit which is on the side of the binocular head 16. Light from the light source 18 for vertical overhead illumination is focussed on the specimen by adjusting the illumination side objective lens 8. The image of the light reflected from the concave mirror 11 is superposed upon the image of the light reflected from the specimen by adjusting the transmission side objective lens 10. Thereafter, the optical path switch 17 is switched to the laser light side.
Alternatively, the transmission side objective lens 10 is preliminarily adjusted to a position suitable for the preparation having a standard thickness. Focussing is achieved by means of the optical microscope unit including the illumination side objective lens 8. Light is then switched to laser light. The transmission side objective lens 10 is finely adjusted to provide the highest resolution while observing the image on the synthetic monitor.
Such conventional systems have a problem in that focussing adjustment by means of the transmission side objective lens 10 is troublesome and focussing accuracy is low, resulting in difficulty in providing a high resolution.
The present invention was made to overcome the above mentioned problem.
It is an object of the present invention to provide a transmission type confocal laser microscope in which adjustment of the transmission side objective lens for focussing can be achieved easily, accurately and stably.