JPH038595B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a laser pulse width shortening device.

[Conventional technology]

Conventionally, short pulse laser light has been generated by a passive mode-locking method using a saturable dye. However, this method is inferior in stability and reliability, so a forced mode-locking method in which forced modulation is applied from the outside has been adopted. On the other hand, with this forced mode locking method, only pulses with relatively long pulse widths can be obtained. Therefore, in order to obtain a pulse with an extremely short width, it is necessary to perform some kind of pulse width reduction.

The following two methods have been used to shorten pulse widths in the past.

The first method is to shorten the pulse width by using two diffraction gratings to create an optical path difference depending on the frequency of a pulse whose frequency is changed over time by passing it through an optical fiber.

The second method involves shortening the pulse width by passing the saturable dye multiple times.

[Problem that the invention seeks to solve]

By the way, each of the above methods is effective, but requires skill in adjustment and cannot be incorporated into an oscillator. Furthermore, there were other problems such as an increase in price.

The present invention was made in order to solve the above-mentioned problems, and it is an object of the present invention to provide a laser pulse width shortening device that requires only incorporating an etalon into a laser oscillator and requires almost no adjustment.

[Means for solving problems]

First, the principle of this invention will be explained.

Optical materials usually have a nonlinear refractive index that depends on light intensity. Due to this nonlinear refractive index, a laser pulse whose intensity changes greatly within a short period of time undergoes a frequency change corresponding to its intensity derivative.
The resulting frequency shift is zero at the peak of the laser pulse and large on both sides.

The transmittance of an etalon is frequency dependent, and can be considered to be the maximum transmittance when the frequency shift is zero.
When a pulse whose frequency has been shifted due to the nonlinear refractive index passes through the etalon, a shortening of the pulse width occurs. Both sides of a pulse with a large frequency shift are shaved off by the etalon, making the pulse sharp. This effect is
The stronger the light intensity, the more noticeable it is. Even if the compression per time is not that great, sufficient compression can be obtained by increasing the number of times.

[Embodiments of the invention]

Next, one embodiment of the present invention will be described.

FIG. 1 is a schematic diagram showing an embodiment of the present invention. In this figure, 1 is the first reflecting mirror, 2
3 is a rod made of glass or the like as a laser oscillation element, 4 is a Q-switch element, and 5 is a forced mode locking modulation element. Reference numeral 6 denotes a second reflecting mirror which has a lower reflectance than the first reflecting mirror and transmits light. Note that the etalon 2 is arranged not perpendicularly to the optical axis but slightly inclined.

The rod 3 in the resonator constituted by the first and second reflecting mirrors 1 and 6 is excited by a flash lamp to cause laser oscillation, and the forced mode locking modulation element 5 performs forced mode locking to stabilize the laser beam. oscillates short pulses. Then, Q-switching is carried out using the Q-switching element 4, and the minute laser pulse is made larger. By increasing the size of the pulse, nonlinear optical effects become more pronounced, and the frequency shift within the laser pulse can be increased. As a result, etalon 2
This effectively reduces the pulse width.

FIG. 2 is a reproduction of a photograph of the giant pulse train obtained from the embodiment shown in FIG. 1, and only the upper and lower envelopes are shown. As can be seen from this figure, the pulse, which was small at first, suddenly becomes large when the Q switch is applied by the Q switch element 4, consumes stored energy, reaches a peak, and gradually decreases again. During this process, the pulse width of the laser pulse changes as shown in FIG.

FIG. 3 is a diagram showing changes in pulse width with respect to the position of the pulse train, and time 0 is the peak of the pulse train. After the peak of the pulse train, the pulse width decreases. The shortest pulse width has been observed to be 3 picoseconds.
The shortening ratio is about 15 times.

In addition, although the Q-switch element 4 was used in the above embodiment, in order to make the pulse width shortening effect of the etalon 2 noticeable, it is necessary that the pulse intensity be large, and this can be achieved with a single pulse oscillator. This is to do so. Therefore, if a strong laser pulse can be obtained from the beginning, the pulse width can be shortened using only the etalon 2 or a resonator consisting of the first and second reflecting mirrors 1 and 6 sandwiching it. Furthermore, in the above embodiment, one etalon 2
In addition to this, an etalon formed of a plurality of flat plates with glass interposed therebetween or a plurality of parallel gaps provided with air gaps may be used.

〔Effect of the invention〕

As explained above, the present invention is equipped with an etalon consisting of a single or multiple parallel plates or parallel gaps, and by transmitting a pulsed laser beam having a frequency shift through the etalon, the pulse width can be shortened. By doing so, a large pulse width reduction ratio can be obtained with an extremely simple configuration. Further, an arrangement in which the etalon is placed inside the resonator has the advantage of being able to shorten the pulse width more efficiently.

[Brief explanation of the drawing]

FIG. 1 is a schematic configuration diagram showing an embodiment of the present invention, FIG. 2 is a reproduction of a photograph of a pulse train generated from the oscillator of this invention, and FIG. 3 is a graph showing how the pulse width decreases. . In the figure, 1 and 6 are reflecting mirrors, 2 is an etalon, 3 is a rod, 4 is a Q switch element, and 5 is a forced mode locking modulation element.

Claims (1)

[Claims] 1. A laser comprising an etalon consisting of a single or multiple parallel plates or parallel gaps that shortens the pulse width by transmitting a pulsed laser beam having a frequency shift. Pulse width shortening device. 2. A laser characterized in that an etalon consisting of a single or multiple parallel plates or parallel gaps is arranged in a resonator to shorten the pulse width by transmitting a pulsed laser beam having a frequency shift. Pulse width shortening device. 3. The laser pulse width shortening device according to claim 2, wherein the resonator is equipped with a Q switch.