Radiant energy – Photocells; circuits and apparatus – Photocell controls its own optical systems
Reexamination Certificate
2000-09-07
2002-07-30
Le, Que T. (Department: 2878)
Radiant energy
Photocells; circuits and apparatus
Photocell controls its own optical systems
C250S205000
Reexamination Certificate
active
06426490
ABSTRACT:
The invention relates to a method for operating a preferably confocal laser scanning microscope, the laser system comprising at least one solid-state laser or a diode laser.
In confocal laser scanning microscopy, gas lasers are most often used as illumination sources. The gas lasers take up a quite considerable amount of space, not least because of their gas tube. As a result, compact device designs of the gas lasers cannot be implemented. Furthermore, gas lasers have only a short service life, which results in quite considerable operating costs. In addition, gas lasers need intensive cooling during operation and require complicated air or water cooling, which in turn on the one hand entails costs and on the other hand increases the space requirement of such a laser system. Finally, lasers have a high energy consumption and, at the same time, only a low efficiency.
In addition to the conventional gas lasers, there are also already solid-state lasers. Until now, these have hardly been used in confocal laser scanning microscopy, since these always exhibit intensity fluctuations during the measurement process and these in turn distort the measurement result or superimpose interfering patterns on the actual image information. Stable-intensity solid-state lasers require complicated control mechanisms, which at least largely prevent the occurrence of spiking or relaxation fluctuations. In the embodiments known hitherto from practice, controlled solid-state lasers are complicated and expensive. Uncontrolled solid-state lasers have the drawback of a periodic mode concurrence, which always leads to a pulsed intensity behavior. Although adequate long-term stability can be achieved by means of periodic modulation of the pump light source, this then leads, because of the spiking and because of the relaxation oscillations, to a considerable short-term increase in the laser intensity which, in the case of use in confocal laser scanning microscopy, is associated with undesired interference effects in the process which yields the image. This is not acceptable in the case of the use in confocal laser scanning microscopy.
Spiking and relaxation oscillations are phenomena which are characteristic of most solid-state lasers and semiconductor lasers. In these phases, the recovery times for the population inversion of the excited state are substantially longer than the decay time of the laser resonator. These phenomena do not occur in gas lasers, so that when gas lasers are used, this problem has hitherto been paid hardly any attention.
Irrespective of the application in laser scanning microscopes, approaches to suppressing the spiking behavior of solid-state lasers have already been made. For this purpose, a nonlinear absorber has been inserted into the laser resonator to cause high losses at high intensities. Ultimately, this is a passive solution. Furthermore, an external control loop has already been provided, which operates with a detector and a loss modulator within the resonator. This is an active solution. Even small nonlinear loss elements damp the relaxation behavior considerably. As a result, this approach can be used only conditionally, since hitherto there were no good, rapidly acting optical limiters which have a low threshold value and, within a laser resonator, exhibit sufficiently low losses at the desired intensities. The external control, in accordance with which a loss modulator is provided outside the laser resonator, is therefore possible in principle but is in general complicated and expensive in operation. A stable mechanical design of the laser, acoustic insulation and stable current sources help to minimize the disadvantageous effects.
When frequency-doubling laser systems are used, active stabilization is technically extremely complicated, particularly when it is carried out for an external resonator. When quasi phase-adapted materials are used, a single passage through the nonlinear crystal is also possible, but this is inefficient and barely provides the necessary optical powers.
SUMMARY OF THE INVENTION
The present invention is therefore based on the object of specifying a method for operating a preferably confocal laser scanning microscope according to which the use of a solid-state laser or of a diode laser is possible and according to which undesired distortions of the image information are effectively avoided.
The above object is achieved by the features of patent claim
1
. According to said claim, a generic method—using a solid-state laser or a diode laser—is characterized in that the scanning procedure or the recording of data is synchronized with the phase of an at least largely continuous emission of intensity from the laser system.
According to the invention, the synchronization of scanning procedure or data recording and a continuous emission of intensity from the laser system or the laser light source is provided. This achieves the situation where the data recording is synchronized with the time window of a quasi continuous emission of intensity from the solid-state laser or a diode laser, as a result of which no intensity fluctuations of the laser system occur during the measurement process. To this extent, distortion of the measurement result is ruled out.
According to the invention, it is now possible, instead of conventional gas lasers, to use solid-state or diode lasers in the confocal laser scanning microscope. Their suitability for confocal laser scanning microscopy depends on the stability of the intensity of the emitted laser radiation. While simple solid-state lasers without stabilization mechanisms typically exhibit interference in the image intensity when an image is recorded in conjunction with a confocal laser scanning microscope, said interference being attributable to spiking and relaxation fluctuations, these phenomena are avoided when data is being recorded from the confocal laser scanning microscope in the manner according to the invention, because the intensity fluctuations of the laser output, which are mostly regular, are compensated for by means of synchronization. This is ultimately achieved by unavoidable interference, as is generally unavoidable when conventional intensity control systems are used, specifically occurring at a defined point in time. With the knowledge of this situation the time window for the actual recording of the data begins—intentionally or in a controlled manner—only after the outlined interfering phase.
In concrete terms, the laser system, comprising a solid-state laser or a diode laser, and the data recording system are synchronized by a control unit, so that the data is recorded in the phase of the at least largely continuous emission of intensity from the laser system. With regard to the synchronization to be carried out, there are in principle two possibilities.
On the one hand, the natural oscillations of the laser system could be adjusted in such a way that the peak behavior of the laser can be used as a trigger pulse or as a synchronization pulse for the data recording system. By utilizing the preferably adjustable natural oscillations of the laser system, its peak behavior supplies a synchronization pulse for the data recording. The synchronization pulse could be fed indirectly or directly from the laser system to the data recording system. In concrete terms, the laser light source or the laser could have a synchronization output, which is connected via a line to the control unit. In this case, the laser could be adjusted such that a periodically repeating laser output intensity waveform occurs. The peak behavior or the spike of the laser is in this case used for synchronization, to be specific preferably via the control unit provided there, as a result of which the recording of the data from the laser scanning microscope is triggered.
On the other hand, the synchronization may be implemented by the laser system used being deliberately influenced by the control unit. To this extent, the laser system receives, via the control unit, a synchronization pulse whereupon, after a dead time, the at least larg
Foley & Lardner
Leica Microsystems Heidelberg GmbH
LandOfFree
Method for operating a preferably confocal laser scanning... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Method for operating a preferably confocal laser scanning..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Method for operating a preferably confocal laser scanning... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2856498