JPH10294517A - Laser beam emitter - Google Patents

Abstract

PROBLEM TO BE SOLVED: To make feasible the stable control of longitudinal mode distribution including the oscillation of Q switch laser in a plurality of frequency and central frequency and wavelength width, by a method wherein the outgoing beams from an injected wave beam source is synchronously injected with the Q switch laser beam source. SOLUTION: A laser beam emitter is composed of Q switch laser part 1 and an injecting laser part 2 as an injecting laser wave beam source for synchronously injecting with the Q switch laser part 1. Next, the outgoing beams from a resonator 2 of the injecting laser part 2 are led into the resonator of the Q switch laser 1 as the injecting beams by reflection using a mirror 3 and a polarizer 17 or the mirror 23 only, while passing through an isolator 5 and a beam modulator 26 provided if necessary. In such a constitution, the beams having the spectrum exceeding two frequencies are used as the injecting beams so that wavelength distribution of the injecting beams and the resonator mode in the Q switch laser part 1 may be duplicated, thereby enabling the Q switch laser part 1 to be oscillated in a plurality of modes.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to various scientific instruments,
The present invention relates to a laser light generator used as a light source for an exposure device, a lighting device, a display device, and the like.

[0002]

2. Description of the Related Art Conventionally, a Q-switched laser light source has been used as a single longitudinal mode continuous wave laser light source (T.Kane , RLByer, Optics L
etters, Vol. 10, pp65-67, (1985).), which is capable of injection-locking (injection seeding) continuous-wave laser light emitted from it to generate a single-mode Q-switched pulse light. (Lightwave Electronics product catalog, Model-101).

In order to produce a laser light source that oscillates in a mode other than the single mode, for example, in a plurality of modes having a fixed frequency difference, it has been necessary to control a birefringent filter, an etalon, or the like singly or in combination. (Solid-St
ate Laser Engineering, 3rd Edition, Springer Verla
g.).

In order to make a Q-switched laser light source in a plurality of modes, the emitted light is converted to an acousto-optic modulator, so-called AOM.
Also, there is a report that the light is passed through a phase modulator such as an electro-optic modulator, so-called EOM.

[0005]

As described above, the injection locking of the Q-switched laser is to inject a longitudinally single-mode continuous wave laser to generate a vertically single-mode Q-switched pulse light. Therefore, the center wavelength can be stabilized, but the wavelength width is reduced to a value substantially determined by the pulse width. However, depending on the application field as a light source, it is necessary to simultaneously control speckle reduction and chromatic aberration by controlling the wavelength width within a certain range, and there is also a scientific field in which the number of specific longitudinal modes is a desired number. . At this time, the single mode Q switch pulse may not be used as it is. If injection locking is not used, multimode oscillation including many longitudinal modes will occur, which will also be larger than the desired wavelength width.

On the other hand, in order to solve this problem, there is a method of controlling the wavelength width by modulating a Q-switch laser output pulse of longitudinal single mode oscillation using an electro-optical element or the like.
If the spire value of the pulse output of the switch laser becomes high, problems such as damage to the optical element and the like become significant. In addition, when the electro-optic crystal absorbs a high-frequency modulation electric field, the element generates heat, and a beam gradient or the like easily occurs due to a thermal gradient.

Accordingly, the present invention has been proposed in view of the above situation, and it is possible to oscillate a Q-switch laser at a plurality of frequencies and to obtain a longitudinal mode distribution including a center frequency and a wavelength width. It is an object of the present invention to solve the problem of providing a laser light generator capable of stably controlling the laser beam.

[0008]

In order to solve the above-mentioned problems, a laser light generating apparatus according to the present invention comprises a plurality of Q-switched laser light sources which are injection-synchronized with a Q-switched laser light source. The injection wave light source emits emission light having a wavelength spread over a plurality of resonator longitudinal modes of the Q-switched laser light source.

[0009] Further, a laser light generating device according to the present invention comprises:
The injection-wave laser light source oscillates at a plurality of frequencies by synchronizing the emission light of the injection-wave laser light source with the Q-switch laser light source and oscillating the Q-switch laser light source at a plurality of frequencies. It was decided that.

That is, in the laser light generator according to the present invention, the Q-switched laser light source can be oscillated at a plurality of frequencies, and the longitudinal mode distribution including the center frequency and the wavelength width is stably controlled. be able to.

[0011]

Embodiments of the present invention will be described below with reference to the drawings.

As shown in FIG. 1, a laser light generating apparatus according to the present invention has a Q-switch laser unit 1 serving as a Q-switch laser light source and injection locking with respect to the Q-switch laser unit 1, that is, injection seeding. And an injection laser unit 2 serving as an injection wave light source for performing the above.

In the Q-switched laser section 1, light emitted from an excitation light source 11 is applied to a laser medium 12, which emits fluorescent light. This laser medium 1
The fluorescence emitted from the laser medium 2 is amplified by stimulated emission while being reflected between the resonator mirrors 13 and 14 arranged before and after the laser medium 12, and is amplified by the stimulated emission. The part is extracted as output light.
The Q-switch laser unit 1 can be composed of, for example, a neodymium yag laser (Nd: YAG laser), a neodymium panadate laser (Nd: YVO ₄ laser), or the like.

A plurality of λ / 4 plates, ie, a plurality of λ / 4 plates, are located between the resonator mirrors 13 and 14 before and after the laser medium 12.
Quarter wave plates, QWP18, 18 are provided.
Also, as shown in FIG. 2, between the QWP 18 on the rear side of the laser medium 12 and the resonator mirror 13 on the rear side in this example, a Q switch, for example, an acousto-optic modulator, so-called AOM, Electro-optic modulator, so-called EOM
15 or a Pockels cell and a polarizer 17 are provided. These are often placed between the QWP 18 on the front side of the laser medium 12 and the resonator mirror 14 on the front side in FIG. Further, the distance between the resonator mirrors 13 and 14, ie, the resonator length, can be controlled by an element for moving and operating the resonator mirror 13, usually an actuator 24 composed of a piezoelectric element (so-called PZT).

As an example of the Q-switch operation, when the Q-switch 15 is off, as shown in FIGS. 6A and 6B, the polarization state of the passing beam changes or is deflected and the resonator is deflected. The loss increases and the Q-switched laser does not oscillate. At the moment when the Q switch 15 is turned on, as shown in (a) and (b) of FIG. 7, the externally injected light is cut off, and the injected light which has already entered the resonator is removed from the resonator. Is reciprocated with low loss, the energy stored in the laser medium 12 is utilized for amplification in the form of stimulated emission, and is extracted as an optical pulse. The operation of the Q switch, the drive and control of the excitation light source 11, and the temperature control of the laser medium 12 are performed by a drive control circuit 16. Actuator 24
Is controlled by the drive control circuit 16 to precisely control the resonator length based on the rise time of the pulse.

The injection laser unit 2 also includes an excitation light source 21 and a laser resonator 22. The output light beam emitted from the resonator 22 of the injection laser unit 2 passes through the optical isolator 2 and the optical modulator 26 placed as necessary, and passes through the mirror 23 and the polarizer 17 or
The light is reflected by the mirror and introduced into the resonator of the Q-switched laser unit 1 as an injection laser beam. The injection laser unit 2
In a normal case, the beam oscillates in a continuous wave, and a beam is always injected into the Q-switch laser unit 1. In many cases, a monolithic resonator is used as the resonator 22 of the injection laser unit 2. In addition to temperature control, the frequency can be changed by a piezoelectric element or the like.

The injection laser section 2 can be constituted by a solid-state laser such as a neodymium yag laser or a neodymium panadate laser. Further, the injection laser unit 2 may be configured by a laser diode, that is, a semiconductor laser. Further, a tunable laser can be used. In this case, the injection laser unit 2 may oscillate in a continuous wave, but may be a pulse laser that outputs a pulse in synchronization with the output of the Q switch pulse in the Q switch laser unit 1. Further, the injection wave light source is not limited to a laser, and light emission from a light emitting diode, electrons, molecules, ions, or the like may be used.

In the Q-switch laser unit 1, while the Q-switch pulse is rising, the introduction of the beam from the injection laser unit 2 is interrupted, and it is difficult for the Q-switch pulse to return to the injection laser unit 2. Further, the Q switch laser unit 1 is provided with an optical isolator 25 as necessary. When an AOM is used as the Q switch 15 instead of the EOM, a mirror is used instead of the polarizer. At this time, not the polarization control, but the beam path in the cavity of the Q-switched laser changes and the pulse rises.

The following is a brief description of the Q-switched laser. In the Q-switch laser, ions or atoms irradiated by an excitation light source in the laser medium 12 are excited to an excited state. In the case of a solid-state laser, the ions to be excited are substances to which transition metal ions such as chromium and rare earth metal ions such as neodymium are added, and the excitation wavelength is selected so as to effectively absorb the excitation light. The excited ion changes its electronic state to a higher level and stays in the excited state for a certain period of time, but eventually transitions to a lower level while emitting fluorescence by spontaneous emission, and eventually lowers the electron level to the ground state. When light with a wavelength equal to the energy difference between the upper and lower levels is incident during the population inversion where the ion's electronic level is higher in the upper level than in the thermal equilibrium state, it emits light by stimulated emission and transitions to the lower level. At this time, the incident light is amplified. The first light that induces stimulated emission is considered to be spontaneous emission fluorescence, externally injected light, etc.In the former case, the spectrum width is usually wide. When there are many resonator modes, it is easy to oscillate in multiple longitudinal modes. In the latter case, the gain of the Q-switched laser is easily used in the cavity mode that overlaps the wavelength or wavelength distribution of the injected light. The laser can also be oscillated in the longitudinal single mode. At this time, it is necessary to match one of the wavelength of the injected light and the resonator mode of the Q-switched laser. For this purpose, the actuator length is often controlled by controlling the resonator length of the Q-switched laser. To determine the moving direction of the actuator, move the actuator back and forth by a small amount,
This is realized by holding the pulse at the point where the decrease in the rise time of the pulse is maximized. Further, when the frequency of the gain center has temperature dependence, a somewhat large gain can be stably used by controlling the temperature of the laser medium so that the oscillation mode comes near the gain center. The vertical single mode Q-switched laser realized in this way is widely used for scientific purposes and the like.

Then, according to the present invention, the Q-switch laser unit 1 can be oscillated in a plurality of modes. That is, light having a spectrum of two or more frequencies is used as the injection light, and the wavelength distribution of the injection light and the resonator mode of the Q switch laser unit 1 are selected so as to overlap with each other. Can be oscillated. If the injection laser section 2 oscillates stably at a plurality of wavelengths, the Q-switch laser section 1 into which the light emitted from the injection laser section 2 has been injected can also stably oscillate. Compared to the wavelength identity required for injection locking, injection locking, that is, the margin of the wavelength difference required for injection seeding is usually wide, so in the case of multiple modes, operation is possible even with a slight frequency difference. is there. The frequency ν (q) of the longitudinal mode of the injection laser unit 2 is given by ν (q) = qc / (2l) (Equation 1), and the wavelength λ (q) is λ (q) = 2l / q (Expression 2) Here, νq is the laser oscillation frequency of the injection laser unit 2, l is the reciprocating or one round resonator optical path length, c is the speed of light in vacuum, and q is a natural number. The frequency of the resonator mode of the Q-switched laser unit 1 is given by ν (Q) = Qc / (2L) (Equation 3), where L is a reciprocating resonator optical path length and Q is a natural number. The wavelength λ (Q) is given by λ (Q) = 2L / Q (Equation 4). The injection laser unit 2 is, as shown in FIG.
q = q1, q2,... qN (however, q1 <q2 <·
.. <QN, N is a natural number of 2 or more, q1, q2,.
.. QN (where Q1 <Q2 <... <QN, where N is 2 or more) as shown in FIG. Natural number,
Q1, Q2,..., QN are natural numbers), and λ (q1) = λ (Q1) and λ (q2) = λ (Q2) (Equation 5) are required. Is not significantly deviated from the gain center wavelength as long as (Equation 5) is satisfied, q1, q2, Q1, Q
2 can be freely selected. Therefore, a desired plurality of modes (Q1, Q2,...) Of the Q-switched laser unit 1
Is determined, from (Equation 1)-(Equation 5), q1 / Q1 = q2 / Q2 = q3 / Q3 =... = QN / QN (Equation 6) What is necessary is just to select the resonator length. Even if the number of modes increases, two types of lasers may be selected according to the same principle.

As means for satisfying the above conditions, a piezoelectric element, so-called PZT
May be provided to control the resonator length of the injection laser unit 2 to control the frequency of the injection laser light. The injection laser light output from the injection laser unit 2 is converted into an acousto-optic modulator, so-called AOM
Alternatively, the frequency may be modulated by an electro-optic modulator, a so-called EOM, or a phase modulator.

When the injection laser section 2 is a laser diode, the output light from the injection laser section 2, that is, the injection laser light has a wavelength spread over a plurality of longitudinal modes of the Q switch laser section 1. It is also possible to have In this case, a plurality of longitudinal modes are oscillated in the Q-switch laser unit 1 within the range of the wavelength spread of the injected laser light.

In this case, by selecting and selecting the oscillation wavelength of the laser diode, the center frequency of the light emitted from the laser diode can be made to substantially coincide with the oscillation gain center of the Q-switch laser light source. In the laser diode, the oscillation wavelength can be selected and selected by adjusting the frequency adjustment current, adjusting the temperature, and adjusting the applied voltage.

When the injection laser unit 2 is a light source that uses light emission from electrons, molecules, ions, and the like, selection and selection of emission wavelengths from electrons, molecules, ions, and the like are performed. The center frequency of the outgoing light of No. 2 is Q
The center of oscillation gain of the switch laser light source can be substantially matched.

Also, as shown in FIG. 5A, the injection laser unit 2 oscillates in a multi-lateral mode and oscillates at a plurality of frequencies, and the same method can be used. Usually Q
Since the cavity length L of the switch laser unit 1 is long and the cavity length 1 of the injection laser unit 2 is short, the longitudinal mode interval of the injection laser unit 2 is several times larger than the cavity mode interval of the Q switch laser unit 1. It becomes wider. Therefore, it is difficult for the Q-switch laser unit 1 to oscillate the longitudinal mode of the injection laser unit 2 that simultaneously excites the resonator longitudinal modes that are close to each other. At this time, by utilizing the transverse mode of the injection laser unit 2, a plurality of modes having an interval smaller than the vertical mode interval of the injection laser unit 2 can be oscillated. 1 only. In this case, the oscillation wavelength Ramudaqmn the injection laser unit 2 is given by λqmn = 2l / [q + (m + n + 1 ) (Arccos (± √g 1 g 2)) / π ] (Equation 7). Here, q, m, and n are natural numbers, q corresponds to the order of the vertical mode, and m and n correspond to the order of the horizontal mode. G ₁ and g ₂ represent the radius of curvature of the mirror constituting the resonator as R
1, given as approximately R2 in the following amounts:

G ₁ = 1-l / R1, g ₂ = 1-l / R2 (Equation 8) As described above, by using the lateral mode of the injection laser unit 2,
By increasing the cavity length of the injection laser unit 2 without reducing the cavity longitudinal mode interval, that is, while keeping the cavity length of the injection laser unit 2 at an appropriate size, FIG.
As shown in the middle (b), it is possible to obtain output light of a plurality of wavelengths at narrow frequency intervals from the Q-switch laser unit 1.

For example, as a simple example, R1 = ∞, R2 =
In the case of 50 mm and l = 30 mm, g ₁ = 1 and g ₂ = 0.4
In the case of the TEM10 mode where m = 1 and n = 0, q
The wavelength difference between the TEM00 mode and the TEM00 mode is calculated by calculating (Equation 7), and 0.28 compared to the longitudinal mode interval different by 1 of q.
The wavelength difference becomes twice as small. Therefore, by oscillating the injection laser section 2 in a plurality of transverse modes and injecting the output light of the plurality of wavelengths, it is possible to oscillate the adjacent resonator longitudinal mode in the Q-switch laser section 1 in the transverse fundamental mode. Become.

In this laser light generator, the output light from the Q-switch laser unit 1 is transmitted to frequency control means, for example, an acousto-optic modulator, so-called AOM or electro-optic modulator, so-called EOM or phase modulator. The modulation may be performed using the modulation. By performing such modulation,
The wavelength width can be widened and the number of oscillation modes can be increased. Further, the output light from the Q-switch laser unit 1 may be subjected to wavelength conversion using a non-linear optical element, or may generate an n-th harmonic (where n is an integer of 2 or more). As described above, when the wavelength of the output light from the Q-switch laser unit 1 is converted, the oscillation wavelength of the injection laser unit 2 can be selected according to the wavelength after the wavelength conversion.

[0029]

As described above, in the laser light generator according to the present invention, the Q-switch laser light source can be oscillated at a plurality of frequencies, and the longitudinal mode distribution including the center frequency and the wavelength width is obtained. It can be controlled stably.

Therefore, in this laser light generator, it is possible to stably control the wavelength width of output light to a desired range over a wide wavelength range. Further, in this laser light generating device, in some cases, it is possible to control the wavelength width more precisely by passing the Q-switch output light in a plurality of modes through the modulation element.

Further, in this laser light generating device, since modulation at a high frequency can be avoided as compared with the conventional device, the number of components to be used, the price, the deflection of the beam, and the leakage of the high frequency to the outside are reduced. It is possible. In this laser light generator, the efficiency of wavelength conversion can be increased.

This makes it possible to control the coherence characteristics of light in a wide range in the application field, thereby expanding the possibilities for avoiding chromatic dispersion, optimizing wavelength conversion efficiency, removing speckles, and multi-wavelength spectroscopy. You can do it.

[Brief description of the drawings]

FIG. 1 is a plan view showing a configuration of a laser light generator according to the present invention.

FIG. 2 is a perspective view showing a configuration of a main part of the laser light generator.

FIG. 3 is a graph showing a resonator longitudinal mode and an output wavelength distribution of an injection laser unit in the laser light generator.

FIG. 4 is a graph showing a resonator longitudinal mode and an output wavelength distribution of a Q switch laser unit in the laser light generator.

5A is a graph showing a resonator longitudinal mode and a transverse mode and an output wavelength distribution of an injection laser unit in the laser light generator, and FIG. 5B is a graph showing a lateral direction of the injection laser unit in the laser light generator. 6 is a graph showing a resonator longitudinal mode and an output wavelength distribution of a Q-switch laser unit oscillated using a mode.

FIG. 6 is a perspective view showing an optical path when a Q switch is turned off in the Q switch laser unit.

FIG. 7 is a perspective view showing an optical path when a Q switch is turned on in the Q switch laser unit.

[Explanation of symbols]

1 Q switch laser section, 2 injection laser section, 13, 1
4 resonator mirror, 18 QWP, 22 resonator, 24
Actuator, 25 optical isolator, 26 optical modulator

Claims (20)

[Claims] 1. A Q-switched laser light source comprising: a Q-switched laser light source; and an injection-wave light source that emits outgoing light having a wavelength spread over a plurality of resonator longitudinal modes of the Q-switched laser light source. A laser light generator, wherein the Q-switched laser light source is oscillated at a plurality of frequencies in synchronization with the injection of the Q-switched laser light source. 2. The laser light generator according to claim 1, wherein a center frequency of the injection wave light source substantially coincides with an oscillation gain center of the Q-switched laser light source. 3. The laser light generating apparatus according to claim 1, further comprising an adjusting means for making a center frequency of the injection wave light source substantially coincide with an oscillation gain center of the Q-switched laser light source. 4. The laser light generator according to claim 1, wherein the light emitted from the injection wave light source is a continuous wave. 5. The laser light generator according to claim 1, wherein the injection laser light source emits a pulse light injected in synchronization with the light emitted from the Q-switch laser light source. 6. An output light from a Q-switched laser light source that oscillates at a plurality of frequencies is modulated by an acousto-optic device or an electro-optical device provided outside the Q-switched laser light source to change the wavelength distribution of the output light. The laser light generator according to claim 1, wherein 7. The laser light generator according to claim 1, wherein the injection light source and the Q-switched laser light source are Nd: YAG laser or Nd: YVO ₄ laser. 8. An output light from a Q-switch laser light source oscillating in a plurality of modes is wavelength-converted using a nonlinear optical element to generate an output light having a wavelength different from the output light from the Q-switch laser light source. The laser light generator according to claim 1, wherein: 9. An output light from a Q-switch laser light source,
2. The laser beam generator according to claim 1, wherein the wavelength is converted using a nonlinear optical element, and n-th harmonic light (where n is a natural number of 2 or more) having a desired wavelength width is output. 10. A Q-switched laser light source, and an injection laser light source that oscillates at a plurality of frequencies. A laser light generator that oscillates at a frequency. 11. The oscillation frequency of the Q-switched laser light source is ν (Q1), ν (Q2),.
N is a natural number of 2 or more, 1 to N represent the number of oscillation longitudinal modes, and Q1, Q2,... QN represent natural numbers), and the oscillation frequencies of the injection laser light source are ν (q1) and ν (q2). ,
... ν (qN) (where N is a natural number of 2 or more and 1
To N represent the number of oscillation longitudinal modes, and q1, q2,.
When N is a natural number, q1 / Q1 = q2 / Q2 =... = QN / QN (where ν (q) = qc / (2l), ν (Q) = Qc
/ (2L), where c is the speed of light in vacuum, l is the cavity optical path length of the continuous wave laser light source, and L is the cavity optical path length of the Q-switched laser light source. Item 11. The laser light generator according to Item 10. 12. An injection-wave laser light source comprises: a continuous-wave laser light source oscillating at a single longitudinal frequency; The laser beam generator according to claim 10, wherein the laser beam is generated. 13. The oscillation frequency of an injection laser light source is Q
11. The laser light generator according to claim 10, wherein the frequency substantially coincides with the resonator longitudinal mode frequency of the switch laser light source. 14. The laser light generator according to claim 10, further comprising adjusting means for adjusting a relative frequency or an interval between the injection wave laser light source and the Q-switch laser light source. 15. The laser light generator according to claim 10, wherein the injection wave laser light source is a continuous wave light source. 16. The laser light generator according to claim 10, wherein the injection laser light source emits pulse light injected in synchronization with light emitted from the Q-switch laser light source. 17. An output light from a Q-switch laser light source that oscillates at a plurality of frequencies is modulated by an acousto-optic element or an electro-optical element provided outside the Q-switch laser light source to change the wavelength distribution of the output light. 11. The laser light generator according to claim 10, wherein: 18. The laser light generator according to claim 10, wherein the injection laser light source and the Q-switch laser light source are Nd: YAG laser or Nd: YVO ₄ laser. 19. Output light from a Q-switch laser light source oscillating in a plurality of modes is wavelength-converted using a non-linear optical element to generate output light having a wavelength different from the output light from the Q-switch laser light source. 11. The method according to claim 10, wherein
The laser light generator according to any one of the preceding claims. 20. Converting the output light from a Q-switched laser light source to a wavelength using a non-linear optical element, and outputting an n-th harmonic light (where n is a natural number of 2 or more) having a desired wavelength width. The laser light generator according to claim 10, wherein: