JP3260915B2 - Short pulse laser light source - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a short pulse laser light source, and more particularly to a mode-locking short pulse laser light source.

[0002]

2. Description of the Related Art As a short pulse laser light source, a short pulse laser light source using a passive mode-locking or active mode-locking technique is known.

In a passive mode-locked laser light source, a dye solution is arranged as a saturable absorber in a laser resonator,
When a light pulse passes through the dye solution, a loss or a phase modulation automatically occurs according to the pulse waveform, so that a short pulse light is obtained. On the other hand, an active mode-locked laser light source has been put into practical use in which a short pulse light can be obtained by a method using an optical modulation element and forcibly synchronizing a phase by adding a signal in accordance with a light traveling cycle. I have.

Further, as another short pulse laser light source, there is a light source capable of obtaining short pulse light of two wavelengths disclosed in Japanese Patent Application Laid-Open No. 1-147881. This is shown in FIG.
It is configured as, in the laser resonator composed of the mirror M _1, M _2, laser medium 1 and the nonlinear optical medium X and the mirror M ₃ are disposed.

According to this configuration, when the laser medium 1 is pumped, laser resonance light having a frequency (fundamental frequency) determined by the laser medium is generated. When the laser resonance light enters the nonlinear optical medium X, In the nonlinear optical medium X, radiation light (second harmonic; SHG) having a frequency twice the fundamental frequency can be obtained. Here, the mirror _{M 1} is totally reflected light of the fundamental frequency, the mirror _{M 2} is the SHG 1
00% and 25% of the fundamental frequency are reflected, and the mirror M ₃ is S
HG is selectively reflected. 25% mirror M ₂ is of fundamental frequency
Is reflected, a loss occurs according to the pulse waveform, and a short pulse light is obtained.

[0006]

The above-described passive mode-locking method uses a dye solution, but has the problems that the kind of the dye is limited and that the life is short and a stable output cannot be obtained for a long time. . On the other hand, the active mode-locking method has a problem that the structure is complicated and that the mode locking of pulse oscillation is difficult. In addition, none of them can selectively generate and extract short pulse light of a desired wavelength over a wide range.

In Japanese Patent Application Laid-Open No. 1-147881, although the structure is simple, as described above, the pulse is shortened by a mirror having a fixed reflectivity that uniformly reflects light of any intensity. Therefore, there is a problem that short pulse light having a sufficiently narrow pulse time width cannot be obtained.
Further, by setting a nonlinear optical medium X called an SHG crystal in the laser resonator, short pulse light having a frequency twice the fundamental frequency can be obtained in addition to short pulse light having the fundamental frequency. Was fixed to twice the fundamental frequency. That is, there is a problem that the wavelength of the short pulse light cannot be selected.

SUMMARY OF THE INVENTION The present invention has been made to overcome the above-mentioned problems. A short pulse laser light source capable of performing mode locking by utilizing an optical parametric process and outputting a short pulse light having a sufficiently narrow pulse time width. And a short-pulse laser light source capable of simultaneously outputting multiple wavelengths and selectively generating and extracting short-pulse light having a desired wavelength over a wide range.

[0009]

A first short-pulse laser light source according to the present invention comprises a laser medium, a laser resonator having the laser medium therein, and a nonlinear optical element provided inside the laser resonator. A medium, and extracting means for selectively extracting light generated in an optical parametric process that occurs when light generated from the laser medium is incident on the nonlinear optical medium and re-entering the nonlinear optical medium. The light generated in the optical parametric reverse process generated in the nonlinear optical medium by the re-incidence by the means is fed back to the laser medium. Here, the short-pulse laser light source may be characterized in that an optical means for correcting the group velocity dispersion of the generated light in the optical parametric process is provided on an optical path between the nonlinear optical medium and the extracting means.

A second short-pulse laser light source according to the present invention comprises a laser medium, a laser resonator having the laser medium inside, a nonlinear optical medium provided inside the laser resonator, and a laser. Extraction means for selectively extracting light generated in an optical parametric process that occurs when light generated from the medium is incident on the nonlinear optical medium and re-entering the nonlinear optical medium; and generating light in the optical parametric process. And a selective emission means for selecting one that does not participate in the optical parametric inverse process generated in the nonlinear optical medium by re-incidence by the extraction means and emitting the light from the resonator,
It is characterized in that light generated in the optical parametric reverse process generated in the nonlinear optical medium by re-incident is fed back to the laser medium. Here, the short-pulse laser light source may include a rotating unit for rotating the nonlinear optical medium or a temperature adjusting unit for adjusting the temperature of the nonlinear optical medium. Further, it may be characterized by having one or more optical means for correcting the group velocity dispersion of the generated light in the optical parametric process.

A third short-pulse laser light source according to the present invention provides a laser medium, a laser resonator having the laser medium therein, and a laser medium provided inside the laser resonator. A first nonlinear optical medium that generates an optical parametric process by the incidence of light, an extracting unit that selectively extracts light generated in the optical parametric process, and an incidence of the generated light in the optical parametric process extracted by the extracting unit And a second non-linear optical medium that generates an optical parametric inverse process, whereby the light generated in the optical parametric inverse process is fed back to the laser medium. Here, the short pulse laser light source is provided with optical means for correcting the group velocity dispersion of the generated light in the optical parametric process on an optical path between the first nonlinear optical medium and the second nonlinear optical medium. It may be characterized. The optical path length adjusting means for adjusting the optical path length in the resonator may be provided so that light generated from a laser medium traveling in opposite directions in the optical path may collide in a nonlinear optical medium. .

A fourth short-pulse laser light source according to the present invention provides a laser medium, a laser resonator having the laser medium therein, and a laser medium provided inside the laser resonator. A first nonlinear optical medium that generates an optical parametric process by the incidence of light, an extracting unit that selectively extracts light generated in the optical parametric process, and an incidence of the generated light in the optical parametric process extracted by the extracting unit And a second nonlinear optical medium that generates an optical parametric inverse process, and a light generated in the optical parametric process that occurs in the first nonlinear optical medium.
And a selective emission means for selecting an element that does not participate in the optical parametric reverse process that occurs in the nonlinear optical medium and emitting the light from the resonator, so that light generated in the optical parametric inverse process is fed back to the laser medium. Features. Here, the short-pulse laser light source may include a rotating unit for rotating the first nonlinear optical medium and a rotating unit for rotating the second nonlinear optical medium, and both may be operated in conjunction with each other. . Further, it may be characterized by having a temperature adjusting means for adjusting the temperature of the first and second nonlinear optical media. The optical path length adjusting means for adjusting the optical path length in the resonator may be provided so that light generated from a laser medium traveling in opposite directions in the optical path may collide in a nonlinear optical medium. . Furthermore, it may be characterized by having one or more optical means for correcting the group velocity dispersion of the generated light in the optical parametric process.

[0013]

In the first short pulse laser light source according to the present invention,
When the light generated from the laser medium enters the nonlinear optical medium and an optical parametric process occurs, the ratio of the intensity of the light generated in the optical parametric process to the incident light intensity becomes nonlinear, and the intensity ratio is enhanced by the optical parametric process. The generated light thus extracted is extracted by the extraction means and is incident on the nonlinear optical medium again. Then, the intensity ratio is emphasized again by the optical parametric inverse process, so that the combination of the extracting means (for example, a mirror) and the nonlinear optical medium functions as a mirror whose reflectance increases as the light intensity increases. For this reason, it is possible to generate short pulse light, and from the extracting means,
Light generated from the laser medium and not involved in the optical parametric process is emitted as short pulse light. Also,
Light emitted from the nonlinear optical medium after re-incidence returns to the laser medium and causes stimulated emission.

The wavelength dispersion of the refractive index of each optical element causes the group velocity dispersion of the generated light in the optical parametric process.
The optical means for correcting the group velocity dispersion disposed on the optical path between the nonlinear optical medium and the extracting means corrects the group velocity dispersion and then re-enters the light generated in the optical parametric process into the nonlinear optical medium. Let it.

In the second short-pulse laser light source according to the present invention, in addition to the same operation as that of the first short-pulse laser light source, the selective emission means outputs light generated in an optical parametric process, Those that do not participate in the process are selected and emitted as short pulse light. The light generated in the reverse process returns to the laser medium and causes stimulated emission.

A third short-pulse laser light source according to the present invention differs from the first short-pulse laser light source in that a nonlinear optical medium that causes an optical parametric process and a nonlinear optical medium that causes an inverse process are different. is there. When light generated from the laser medium enters one nonlinear optical medium and an optical parametric process occurs, the ratio of the intensity of the light generated in the optical parametric process to the incident light intensity becomes non-linear, and the intensity ratio is increased by the optical parametric process. The generated light in which is emphasized is extracted by the extracting means, and is incident on the other nonlinear optical medium. Then, since the intensity ratio is emphasized again by the optical parametric inverse process, the combination from the nonlinear optical medium that causes the optical parametric process to the extracting means (for example, a mirror) and further to the nonlinear optical medium that causes the inverse process has a light intensity. The higher the reflectance, the higher the reflectance of the mirror. Therefore, short pulse light can be generated, and light generated from the laser medium and not involved in the optical parametric process is emitted from the extraction means as short pulse light. Further, the light generated in the reverse process returns to the laser medium to cause stimulated emission.

Further, if the optical means for correcting the group velocity dispersion is provided on the optical path between the two nonlinear optical media, the light generated in the optical parametric process will have its group velocity dispersion corrected, The light enters the nonlinear optical medium that causes the reverse process.

In the fourth short-pulse laser light source according to the present invention, in addition to the same operation as the third short-pulse laser light source, the selective emission means is a light generated in an optical parametric process and is involved in the reverse process. Those that are not to be selected are emitted as short pulse light. The light generated in the reverse process does not exit, but returns to the laser medium to cause stimulated emission.

In the second and fourth short pulse laser light sources, the rotating means rotates the medium to adjust the direction of the medium, and the temperature adjusting means adjusts the temperature of the medium.

Further, in the second and fourth short pulse laser light sources, the optical means for correcting the group velocity dispersion corrects the group velocity dispersion of the generated light in the optical parametric process.

In the third and fourth short-pulse laser light sources, the optical path length adjusting means may include an optical path in the resonator so that light generated from the laser medium traveling in opposite directions may collide in the nonlinear optical medium. Adjust the length.

[0022]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A short pulse laser light source according to an embodiment of the present invention will be described below with reference to the accompanying drawings. In the description of the drawings, the same elements will be denoted by the same reference symbols, and redundant description may be omitted.

The first embodiment is an embodiment of the first and second short pulse laser light sources of the present invention. FIG. 1 shows a configuration of a short pulse laser light source according to the present embodiment. As shown, a pair of mirrors M ₁ and M ₂ constitute a laser resonator, in which a laser medium 1, a nonlinear optical crystal X and a polarizing element 2 are installed. The laser medium 1 is, for example, N
d: constituted by a YAG laser rod, in which case the emission wavelength can be λ _OSC = 1064 nm. In addition,
The laser medium 1 is pumped by a light source (not shown).

The polarizing element 2 is used to convert the laser oscillation light into a light having a plane of polarization parallel to the plane of the drawing. This makes it easier for an optical parametric process to occur in the nonlinear optical crystal X. The nonlinear optical crystal X causes forward and reverse optical parametric processes, and the wavelength of the generated light is variable. The details will be described later. Collimating lens L _1, L ₂
Is for narrowing the beam of the laser light to increase the light power density and to enter the nonlinear optical crystal X.

While the mirror M ₁ is a total reflection mirror, the mirror M ₂ is a mirror that selectively reflects light of a specific wavelength. That is, assuming that the reflectances for light of wavelengths λ _S1 and λ _S2 (variable wavelengths) generated by the optical parametric process are R _S1 and R _S2 and the reflectance for light of wavelength λ _OSC (fixed wavelength) is R _OSC , the mirror M _{In the case of No. 2} , R _S1 and R _S2 are high (the light of λ _S1 and λ _S2 is reflected at a high rate), and R _OSC is low (the light of λ _OSC is transmitted at a high rate). In particular,
When the wavelength lambda _OSC of the light from the laser medium 1 is 1064nm, the reflectivity of the mirror M ₂ is as shown in FIG.

Next, the operation of the above embodiment will be described.

Firstly, within the crystal X of Figure 1 having a nonlinear optical effect, the optical parametric _{process, 1 / λ OSC = 1 /} λ S1 + 1 / λ S2 ............ wavelength lambda _S1 in relation (1), Two waves of λ _S2 are generated. By changing the angle θ between the crystal axis c of the crystal X and the excitation light of λ _OSC , λ _S1 and λ _S2 can be tuned. Here, _assuming that the intensities of the respective waves are I _OSC , I _S1 and I _S2 , the conversion efficiency η from λ _OSC light to λ _S1 and λ _S2 light by the parametric process is η = (I _S1 + I _S2 ) / I _{S OSC} ... (2) In the optical parametric process, the conversion efficiency η is proportional to the light intensity I _OSC . That is, the following equation η = κ · I _OSC κ is proportional constant (3). Therefore, the parametric output is as follows: I _S1 + I _S2 = κ · I _OSC ² (4)

At this time, as shown in FIG. 2, the mirror M ₂ has a low reflectance (R _OSC ) for the wavelength λ _OSC and a high reflectance (R _S1 ) for the wavelengths λ _S1 and λ _S2 . , R
_S2 , which is simplified here as R _S ), the intensity of the light reflected from the mirror M ₂ is R _S1 I _S1 + R _S2 I _S2 = R _S · κ · I _OSC ² (5) .

When such reflected light from the mirror M ₂ , that is, light of wavelengths λ _S1 and λ _S2 again enters the crystal X of FIG. 1 having a nonlinear optical effect, a parametric process reverse to that described above is performed. And light of wavelength λ _OSC is generated. Assuming that the conversion efficiency at this time is ξ, the intensity of the light of wavelength λ _OSC coming out of the crystal X is Ｒ · (R _s κ · I _OSC ² ) ² ... ).

Therefore, in the combination of the nonlinear optical crystal X and the mirror M ₂ , the reflectance with respect to the wavelength λ _OSC changes non-linearly with α · I _OSC ³ ... (7). It can be considered as a mirror (a mirror that reflects light at a higher rate with higher intensity).

This has the same effect as mode locking using a saturable absorbing dye as in the prior art, so that short pulse light can be generated. Moreover, as shown in (7), the combination is a nonlinear optical crystal X and the mirror M _2, is a saturable absorber with excellent saturable absorption characteristics. Therefore, a short pulse laser beam having a very narrow pulse time width can be obtained. The short pulse light (wavelength lambda _OSC) is emitted from the mirror M _2.

In the case of FIG. 2, when λ _OSC is the oscillation wavelength of the Nd: YAG laser of 1064 nm, the wavelengths λ _S1 and λ _S2 of the light generated by the parametric mode locking are, for example, 1800 nm and 2602 nm. When this light is incident on the optical crystal X and other optical elements, group velocity dispersion occurs due to wavelength dispersion of the refractive index. Therefore, λ _S1 , λ _S2
The timing at which light re-enters the nonlinear optical crystal X is shifted,
The efficiency of the optical parametric reverse process that occurs in the crystal X decreases. Therefore, if installing optical means (specific forms will be described later.) For correcting group velocity dispersion in the optical path between the nonlinear optical crystal X and the mirror M _2, up efficiency of optical parametric inverse process, as a result The output intensity of the obtained short pulse light can be increased.

The mirror M ₃ has low R _S1 and R _S2 (transmits light of λ _S1 and λ _{S2 at} a high rate) and high R _OSC (reflects light of λ _{OSC at} a high rate). If installed, λ _S1 , λ _S2
Light can also be extracted. That is, simultaneous oscillation of three wavelengths of λ _S1 , λ _S2 and λ _OSC is possible. Further, if the phase matching condition is adjusted by changing the direction of the crystal axis of crystal X or changing the temperature, the wavelengths λ _S1 and λ _S2 can be selected over a wide range, and a multi-wavelength including λ _OSC light is also added. Can be obtained. In the present embodiment, the wavelength is tunable by operating the rotating means 7 (not shown) to change the direction of the crystal axis.

Next, a first modification of the first embodiment will be described. This is an apparatus in which a nonlinear optical crystal for generating a harmonic of λ _OSC light is installed in the resonator of the short pulse laser light source of the first embodiment shown in FIG. FIG. 3 is a diagram showing the configuration of the device of this modification. This device includes:
Is SHG crystal X ₃ is used as a crystal for harmonic generation. In this apparatus, an optical parametric process is caused by light having a wavelength of λ _SHG (= λ _OSC / 2). Here, the second
Assuming that the reflectance for harmonics is R _SHG , mirror M
₂ , R _SHG , R _S1 , R _S2 are high and R _OSC is low. On the other hand, the mirror M ₃ has a high R _SHG and R _{OSC and} a high R _S1 ,
R _S2 is low.

When the light having the wavelength λ _OSC is incident on the SHG crystal X ₃ , the second harmonic of the half wavelength λ _SHG is generated. The light having the wavelength λ _SHG is incident on the nonlinear optical crystal X and causes an optical parametric process. The wavelengths λ _S1 and λ _S2 of the light generated by this process satisfy the relationship of 1 / λ _SHG = 1 / λ _S1 + 1 / λ _S2 (8). Then, the nonlinear optical crystal X and the mirror M
The combination of ₂ can be considered as a mirror whose reflectivity for the wavelength λ _SHG changes non-linearly with α · I _SHG ³ …………………………… (9) It acts as a reflective saturable absorber. The λ _SHG light reflected by this saturable absorber is SHG
The laser beam enters the crystal X ₃ and generates λ _OSC light to cause laser resonance. In this way, short pulse light can be output. And since λ _SHG light has a shorter wavelength than λ _OSC light,
(8) As is clear from the equation, it is possible to obtain a short pulse light having a wavelength shorter than lambda _OSC from the mirror M _3.

The crystal for generating harmonics is not limited to the SHG crystal. For example, the same effect can be obtained by using a nonlinear optical crystal for generating the third and fourth harmonics or a combination thereof. Is obtained.

FIG. 4 is a diagram showing the configuration of a device according to a second modification of the first embodiment. This device uses a laser medium 1
Is a short pulse laser light source using a crystal having a wide oscillation wavelength range, such as titanium sapphire (Ti: Al ₂ O ₃ ). In this device, a wavelength selection element 11 (such as a birefringent filter or a diffraction grating) is provided in a resonator.

When the light generated from the laser medium passes through the wavelength selection element 11, it becomes light having a spectrum width of about several nm around λ _OSC within the oscillation wavelength range. Here, λ _OSC can be arbitrarily selected within the oscillation wavelength range. An optical parametric process is caused by the light having the spectrum width.

In this device, more modes are locked due to the existence of the above-mentioned spectral width. Therefore, it is possible to further narrow the pulse time width. FIG. 5 is a configuration diagram of a short pulse laser light source according to the second embodiment. In this case, in addition to the configuration of the first embodiment, a mirror M ₄ and triangular prism-shaped prisms 3 and 4 as optical means for correcting group velocity dispersion are installed in the laser resonator.

The mirror M ₄ is a total reflection mirror and is provided for setting an optical path in the resonator.

As shown in the figure, the prisms 3 and 4 are installed so that their directions are opposite to each other, and the opposing surfaces are parallel. This prism pair has a λ
Optical means for correcting group velocity dispersion of _S1 and _λS2 light. Group velocity dispersion arising from the lambda _S1, lambda _S2 the time delay of the light, in addition to a reduction in the efficiency of the reverse process as described above, also causes the expansion of the pulse time width of the pulsed light emitted from the mirror M _3.
In this embodiment, the group velocity dispersion is corrected by installing a pair of prisms as described above. Therefore, according to the device of the present embodiment,
The corrective action of the group velocity dispersion by the prism pair, as compared with the case where no correction, can be emitted more pulse time narrower pulse light from the mirror M _3. In this case, the position is not limited to the position shown in FIG. 5, and correction can be made at any position on the optical path, and λ _S1 and λ _S2 light enter even outside the resonator. A similar effect can be obtained by installing in a position. Also, a plurality of such devices may be installed at the positions described above. Further, by installing a prism pair as the optical means for correcting group velocity dispersion in the optical path between the nonlinear optical crystal X and the mirror M _2, increasing the efficiency of the reverse process, lambda _S1, lambda _S2 light and lambda _OSC light Output intensity can be increased.

The second embodiment can be modified in the same manner as the first embodiment, and the same effects can be obtained.

The third embodiment is an embodiment of the third and fourth short pulse laser light sources according to the present invention. FIG. 6 shows a short pulse laser light source according to the present embodiment. In this short pulse laser light source, the laser resonator in the short pulse laser light source of the first embodiment is formed in a ring shape. As illustrated, a laser resonator is formed by the mirrors M ₁ , M ₂ , and M ₃ , and a laser medium 1 is provided therein. Incidentally, the mirror M ₂ is an extracting means, and outputs to the outside by selecting the emission wavelength lambda _OSC from the laser medium 1. Further, the lenses L ₁ and L ₂ are for making the light having the increased optical power density incident on the nonlinear optical crystals X ₁ and X ₂ . And the crystal X ₁
Causes an optical parametric process, and crystal X ₂ causes the reverse process. Further, the lens L _3, L ₄ is a light emitted from the crystal X ₂ back to the original beam diameter, the mirror M ₃ are a selection output means, the laser medium 1 the light of the wavelength lambda _OSC of this light And outputs light of wavelengths λ _S1 and λ _S2 to the outside.

The unidirectional device 5 provided in the optical path is an element that transmits light in only one direction, and is also called an optical isolator or an optical diode, and generally uses a Faraday element. Here, the unidirectional device 5 is not always necessary, but if it is provided, light in the opposite direction can be eliminated, so that unnecessary disturbance between modes can be reduced.

Next, the operation of the above embodiment will be described.

The beam (wavelength λ) emitted from the laser medium 1
_OSC) passes through the unidirectional unit 5, it is reflected by the mirror M _1, the lens L _1, in L ₂ to increase the power density nonlinear optical crystal X
Incident at ₁ . As a result, two beams of wavelengths λ _S1 and λ _S2 are generated in the crystal X ₁ by a parametric process.

The light intensities I _S1 and I _S2 of the respective wavelengths λ _S1 and λ _S2 at this time can be expressed as follows: I _S1 + I _S2 = κ · I _OSC ² (10) The mirror M ₂ has the following characteristics: R _OSC 〜0 (small) R _S1 , R _S2 : R _S (large), and therefore the light intensity after reflection is R _S1 · I _S1 + R _S2 · I _S2 = _RS · (I _S1 + I _S2 ) = R _S · κ · I _OSC ² (11)

In the second nonlinear optical crystal X ₂ , λ _S1 , λ _S2 → λ _OSC by the reverse optical parametric process of the _first crystal X ₁ , and returns to the original wavelength λ _OSC . The light intensity at that time is represented by I _OSC (after X ₂ ) = ξ · ( _RS · κ · I _OSC ² ) ² = α · I _OSC ⁴ (12)

Thus, the light of wavelength λ _OSC emitted from crystal X ₂ passes through lenses L ₃ and L ₄ to have the original beam diameter, is reflected by mirror M ₃ and returns to laser medium 1. Therefore, in the combination of crystal X ₁ → mirror M ₂ → crystal X ₂ , the transmittance is represented by α · I _OSC ³ ... (13), and the higher the incident intensity, the better. Since it can be considered as a mirror that reflects light, that is, a saturable absorber, short pulse light can be generated. Moreover, since it has excellent saturable absorption characteristics as shown in (13), it is possible to obtain short pulse light having a very narrow pulse time width. Simultaneous oscillation of three wavelengths λ _S1 , λ _S2 and λ _OSC is possible. Here, the crystal X ₁ and the crystal X
By adjusting the by Nari changing the temperature Nari changing the orientation of the crystal axes phase matching conditions for _2, wavelength lambda _S1, lambda _S2 can be selected over a wide range, short pulses of multiwavelength plus also lambda _OSC light It is possible to get light. In the present embodiment, the wavelength is variable by changing the directions of the crystal axes of the crystal X ₁ and the crystal X ₂ by operating the rotating means 8 and 9 (not shown) in conjunction. At this time, the adjustment is made in consideration that one crystal axis direction is determined and the other crystal axis direction is also determined because one crystal axis direction is determined because one crystal generates a normal process and the other crystal must generate a reverse process. There is a need.

[0050] In the above embodiment, the mirror M ₃ are selected emitting unit (transmitted lambda _S1, the lambda _S2 light at a high rate, lambda the _OSC light reflected at a high rate.) And was, but for example, fully reflective mirror this However, it is possible to obtain short pulse light. in this case,
Only lambda _OSC light is emitted from the mirror M _2.

In the first embodiment, since only one nonlinear optical crystal is used, the λ _OSC by the optical parametric positive process is used.
Conversion efficiency from light to λ _S1 and λ _S2 light (this depends on κ) and conversion efficiency from λ _S1 and λ _S2 light to λ _OSC light by an optical parametric inverse process (this depends on ξ) .)
Are determined by the type of nonlinear optical crystal. On the other hand, in the present embodiment, since the crystal for the normal process and the crystal for the reverse process are separated, a combination of κ and ξ can be selected, whereby the desired short-pulse light The output intensity can be further increased.

As in the case of the first embodiment, the λ _S1 and λ _S2 light generated in the third embodiment have different group velocities while passing through each optical element. Therefore, in the fourth embodiment, as shown in FIG. 7, the optical means for the group velocity dispersion correction on the optical path between the crystal X ₁ and the crystal X ₂ (for example, a prism pair described above) are set up. Thereby, for the reason described in the first embodiment, the efficiency of the optical parametric reverse process is increased, and the output intensity of the resulting short pulse light can be increased.

In the devices of the third and fourth embodiments, when λ _S1 and λ _S2 light are output using the mirror M ₃ as the selective emission means, the group velocity dispersion of the λ _S1 and λ _S2 light is equal to the emission. Λ _S1 and λ _S2 appear as a time delay, and as a result, the pulse time width expands. This is as described in the second embodiment. Therefore, similarly to the second embodiment, a prism pair for group velocity dispersion correction is installed on the optical path inside the resonator or at a position where the emitted λ _S1 and λ _S2 light enters even outside the resonator. By correcting the time delay of λ _S1 and λ _S2 light,
It can be emitted more pulse time narrower pulse light from the mirror M _3.

FIG. 8 shows a fifth embodiment.
In this apparatus, the unidirectional device 5 is removed from the configuration of the third embodiment, and an optical path length adjusting means 10 is provided instead. Further, a configuration is shown in which the λ _OSC light travels in both directions on the optical path, and each of them is mode-locked by an optical parametric process to shorten the pulse.

In this apparatus, the optical path length adjusting means 10 comprises total reflection mirrors M ₅ and M ₆ and a right angle prism 6. The total reflection mirrors M ₅ and M ₆ are installed in a C shape so that the optical path direction and the normal direction of each mirror surface cross each other at an angle of 45 degrees. The right-angle prism 6 is a prism having a triangular prism shape having a bottom surface of a right-angled isosceles triangle. Of the surfaces constituting the triangular prism, two surfaces including the isosceles of the bottom surface and perpendicular to the bottom surface generate total reflection. In addition, the right-angle prism 6 is variable in the vertical direction in the figure so that the optical path length can be arbitrarily adjusted. According to this, light incident on one mirror is reflected perpendicularly to the incident direction and is incident on the prism.
The light changes its direction in the prism, is incident on the other mirror perpendicular to the incident direction, is reflected by the mirror, and travels again in the incident direction. In this way, when the light passes through the prism, the optical path length of the light becomes longer. The optical path length can be arbitrarily increased by changing the position of the right-angle prism 6.

[0056] Using this, clockwise and counterclockwise pulse light shown, for example, to adjust the optical path length so as to collide with the non-linear optical crystal X _1, increased the intensity of light at the moment of the collision both pulsed light There was increased more nonlinear effect at the time of collision, increases the intensity of the generated light in the crystal X _1. As a result, the intensity of the short pulse light also increases. Since the unidirectional device 5 is removed, the above-described disturbance between the modes traveling in both directions is a concern. Generally, it is more effective to increase the nonlinear effect than to suppress the disturbance between the modes. large. Therefore, in this embodiment, it is possible to further narrow the pulse time width. The position of the optical path length adjusting means 10 is not limited to the position shown in FIG. Further, as the optical path length adjusting means, the above-described one is merely an example, and other optical path length adjusting means may be used.

[0057] Further, although the selection output means the mirror M ₃ in FIG. 8, the mirror M ₃ are as short pulse laser light source
It may be a total reflection mirror for example, in this case and only lambda _OSC light is emitted from the mirror M ₂ as a short pulse light.

[0058] Figure 9 shows a sixth embodiment, which in the short-pulse laser light source of the fifth embodiment, a prism pair for group velocity dispersion compensation on an optical path between the crystal X ₁ and the crystal X ₂ Is installed. Also in this case, similarly to the above-described embodiment, the efficiency of the optical parametric reverse process can be increased, and the output intensity of the obtained short pulse light can be increased.

Further, in both the fifth and sixth embodiments, the mirror M
_In the case of outputting λ _S1 and λ _S2 light by using ₃ as the selective emission means, a pair of prisms for group velocity dispersion correction is output on the optical path inside the resonator or λ _S1 and λ _S2 even outside the resonator. lambda _S1 installed in a position such light is incident, by correcting the time delay lambda _S2 light can be emitted more narrow pulse time width pulse light from the mirror M _3.

The present invention is not limited to the above embodiment. For example, similarly to the second embodiment, in the short pulse laser light sources of the fourth and sixth embodiments, a prism pair is further provided with each optical element. By placing the prism pairs between them, a plurality of prism pairs may be provided as a whole. In the above embodiment, the pair of triangular prisms is used as the optical means for correcting the group velocity dispersion. However, the optical means for correcting the group velocity dispersion is not limited to this. In addition, the third, fourth, fifth and sixth
In the embodiment, modifications similar to those in the first embodiment are possible. However, when performing the first variant, each optical path between the laser medium 1 and the optical path and the laser medium 1 between the nonlinear optical crystal X ₁ and the nonlinear optical crystal X _2, the crystals for harmonic generation Install. At this time, each of the harmonic generation crystals generates a harmonic when light generated from the laser medium is incident, and a harmonic when the harmonic generated by the other harmonic generation crystal is incident. They are arranged in such a way as to cause the reverse process of occurrence. The fifth, when performing a second modification to the sixth embodiment, each optical path between the laser medium 1 and the optical path and the laser medium 1 between the nonlinear optical crystal X ₁ and the nonlinear optical crystal X ₂ Next, a wavelength selection element is provided.

The method of the above embodiment can be applied to a solid-state laser excited by a semiconductor laser, an excimer laser, or a gas laser, and the type of laser is selected according to the wavelength range to be obtained.

[0062]

As described above in detail, according to the first short pulse laser light source of the present invention, the saturable absorber is constituted by using the nonlinear optical medium having the optical parametric action and the extracting means. In addition, the light emitted from the laser medium is reflected at a higher rate as the light intensity is higher, and the ratio (saturable absorption characteristic) at which the reflectivity becomes higher according to the light intensity is excellent, and the pulse time width is extremely high. A short pulse laser light source that generates narrow short pulse light can be realized. Furthermore, if the optical means for group velocity dispersion correction is arranged on the optical path between the nonlinear optical medium and the extracting means, the light generated in the optical parametric process can be
After correcting the group velocity dispersion, it is possible to correct the timing deviation and re-enter the nonlinear optical medium, thereby realizing a short-pulse laser light source with high output.

According to the second short pulse laser light source of the present invention, since the selective emission means is provided in addition to the first short pulse laser light source, the light having the wavelength of the light generated in the optical parametric process is provided. Can also be emitted as short pulse light. Further, if the direction of the nonlinear optical medium is changed by a rotating means or the like, or the temperature condition is changed by a temperature adjusting means, and the phase matching condition is adjusted, it becomes possible to select the wavelength of the short pulse light to be emitted. A short pulse laser light source can be realized.

According to the third short-pulse laser light source of the present invention, a nonlinear optical medium that generates an inverse process is provided separately from a nonlinear optical medium that generates an optical parametric process. By selecting each medium, the conversion efficiency in the forward process and the reverse process can be independently selected, and a short-pulse laser light source with high output can be realized. Furthermore, if the optical means for correcting the group velocity dispersion is disposed on the optical path between the nonlinear optical medium for the optical parametric positive process and the nonlinear optical medium for the inverse process, the light generated in the optical parametric process will After correcting the velocity dispersion, it is possible to correct the timing deviation and to enter the nonlinear optical medium for the reverse process, so that a short-pulse laser light source with high output can be realized.

According to the fourth short-pulse laser light source of the present invention, since the selection means is provided in addition to the third short-pulse laser light source, it is the same as the second short-pulse laser light source with respect to the first. The effect is obtained.

In the second and fourth short pulse laser light sources, if the optical means for correcting the group velocity dispersion is appropriately arranged, the group velocity dispersion of the generated light in the optical parametric process is corrected and the generated light is corrected. Is corrected, a short pulse light with a narrower pulse time width can be obtained.

In the third and fourth short-pulse laser light sources, if the optical path length adjusting means is provided, the laser resonance lights traveling in opposite directions collide with each other in the nonlinear optical medium, and the nonlinear effect is obtained. Since the pulse width can be increased, short pulse light with a narrower pulse time width can be obtained.

According to the single pulse laser light source as described above, several tens of ps (picoseconds) to several ps, and further, fs
(Femtosecond) order tunable short pulse laser light can be obtained. Therefore, it can be widely used in the field of high-speed or precise optical measurement.

[Brief description of the drawings]

FIG. 1 is a configuration diagram of a short pulse laser light source according to a first embodiment.

FIG. 2 is a characteristic view of the mirror M _2.

FIG. 3 is a configuration diagram of a short pulse laser light source according to a first modification of the first embodiment.

FIG. 4 is a configuration diagram of a short pulse laser light source according to a second modification of the first embodiment.

FIG. 5 is a configuration diagram of a short pulse laser light source according to a second embodiment.

FIG. 6 is a configuration diagram of a short pulse laser light source according to a third embodiment.

FIG. 7 is a configuration diagram of a short pulse laser light source according to a fourth embodiment.

FIG. 8 is a configuration diagram of a short pulse laser light source according to a fifth embodiment.

FIG. 9 is a configuration diagram of a short pulse laser light source according to a sixth embodiment.

FIG. 10 is an explanatory diagram of a conventional example.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Laser medium, 2 ... Polarization element, 3,4 ... Prism, 5
... unidirectional device, 6 ... right angle prism, 7, 8, 9 ... rotating means,
10 ... optical path length adjusting means, 11 ... wavelength selection element, X ... nonlinear optical medium, M _2, M ₃ ... wavelength selective mirror.

──────────────────────────────────────────────────続 き Continued on the front page (58) Field surveyed (Int. Cl. ⁷ , DB name) H01S 3/00-3/30 G02F 1/35 JICST file (JOIS)

Claims (12)

(57) [Claims] 1. A laser medium, a laser resonator having the laser medium therein, a nonlinear optical medium provided inside the laser resonator, and light generated from the laser medium being incident on the nonlinear optical medium. Extraction means for selectively extracting light generated in the optical parametric process that occurs when the light is generated and re-entering the nonlinear optical medium, wherein optical parametric light generated in the nonlinear optical medium by re-incidence by the extraction means A short-pulse laser light source characterized in that light generated in the reverse process is fed back to the laser medium. 2. The optical system according to claim 1, further comprising an optical unit for correcting a group velocity dispersion of light generated in the optical parametric process on an optical path between the nonlinear optical medium and the extracting unit. Short pulse laser light source. 3. A laser medium, a laser resonator having the laser medium therein, a nonlinear optical medium provided inside the laser resonator, and light generated from the laser medium being incident on the nonlinear optical medium. Extraction means for selectively extracting light generated in the optical parametric process that occurs when the light is generated and re-entering the nonlinear optical medium; and light generated in the optical parametric process and re-incident by the extraction means. A selective emission unit that selects one that does not participate in the optical parametric reverse process that occurs in the nonlinear optical medium and emits the light from the resonator, and feeds back the generated light in the optical parametric reverse process to the laser medium. A short pulse laser light source characterized in that: 4. The short-pulse laser light source according to claim 3, further comprising a rotating unit that rotates the nonlinear optical medium. 5. The short-pulse laser light source according to claim 3, further comprising a temperature adjusting means for adjusting a temperature of the nonlinear optical medium. 6. A laser medium, a laser resonator having the laser medium therein, and a first optical resonator provided inside the laser resonator, wherein an optical parametric process is caused by incidence of light generated from the laser medium. And the nonlinear optical medium of
Extracting means for selectively extracting light generated in the optical parametric process; and a second nonlinear optical medium which generates an optical parametric reverse process by incidence of the light generated in the optical parametric process extracted by the extracting means. A short-pulse laser light source, characterized in that light generated in the optical parametric reverse process is fed back to the laser medium. 7. An optical means for correcting group velocity dispersion of generated light in the optical parametric process is provided on an optical path between the first nonlinear optical medium and the second nonlinear optical medium. The short pulse laser light source according to claim 6, wherein 8. A laser medium, a laser resonator having the laser medium therein, and a first optical resonator provided inside the laser resonator, which generates an optical parametric process by incident light generated from the laser medium. And the nonlinear optical medium of
Extracting means for selectively extracting light generated in the optical parametric process; and a second nonlinear optical medium which generates an optical parametric reverse process by incidence of the light generated in the optical parametric process extracted by the extracting means. Selecting a light generated in the optical parametric process generated in the first nonlinear optical medium and not participating in the optical parametric reverse process generated in the second nonlinear optical medium, and outputting the light from the resonator. A short-pulse laser light source, comprising: an emission unit, wherein the light generated in the optical parametric reverse process is fed back to the laser medium. 9. A rotating device for rotating the first nonlinear optical medium and a rotating device for rotating the second nonlinear optical medium, both of which are operated in conjunction with each other. Short pulse laser light source. 10. The short-pulse laser light source according to claim 8, further comprising a temperature adjusting means for adjusting the temperatures of said first and second nonlinear optical media. 11. An optical path length adjusting means for adjusting an optical path length in the resonator, wherein light generated from the laser medium traveling in the optical paths in opposite directions collides in a nonlinear optical medium. 6. The method of claim 6, 7, 8, 9 or 1.
0 short pulse laser light source. 12. The apparatus according to claim 3, further comprising one or more optical means for correcting a group velocity dispersion of light generated in the optical parametric process.
2. The short pulse laser light source according to 1.