JPH01143376A - Laser light source - Google Patents

Abstract

PURPOSE:To generate a resonance laser beam mode-locked to be adapted for the cavity length of a resonator by periodically exciting a laser body to be excited by a semiconductor laser by the resonance frequency of the resonator. CONSTITUTION:An exciting semiconductor laser 8 is controlled by a modulation signal S11 having a predetermined frequency to be determined on the basis of the resonance frequency (f) of a resonator CAV thereby to generate a resonance laser beam LA longitudinally mode-locked to the resonator CAV, and the light LA1 is radiated as an output laser light LA2. When the light LA1 generated by a laser body 1 is reciprocated in the resonator CAV having a cavity length L to be returned to the body 1, the essential part of the body 1 is excited by the laser 8, it is strengthened by the laser beam generated newly at the body 1, while the laser beam of other mode is not strengthened thereby, but weakened. Thus, the mode-locked output laser LA2 can be obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION A. Field of Industrial Application The present invention relates to a laser light source, and in particular to a laser light source that is capable of stabilizing the resonance mode inside a resonator.

B. Summary of the Invention The present invention provides a laser light source that emits a laser beam generated from a laser body as an output laser beam, in which the laser body is excited by a laser beam for excitation of a semiconductor laser driven at the resonant frequency of a resonator. By doing so, mode-locked output laser light can be obtained with a simple configuration.

C. Prior Art Conventionally, solid-state lasers have the characteristics of being able to emit an output laser beam with relatively high efficiency, and being able to obtain a beam with good optical characteristics such as coherence range with a relatively compact configuration. Based on this, it is considered to be applied to various uses.

For example, if a second harmonic can be generated inside a resonator of a solid-state laser, it is possible to obtain an output laser beam having a wavelength of 1/2 of the fundamental wavelength with the high efficiency that solid-state lasers have.

However, when trying to apply a solid-state laser to such a purpose, there is a problem in that the output laser light actually contains noise that appears to be due to mode competition.

Possible methods for removing this noise include shortening the cavity length in the longitudinal mode direction of the resonator and providing so-called mode-locking by providing an internal modulator inside the resonator.

However, in practice, it is difficult to shorten the cavity length of the resonator due to mechanical processing accuracy.
The mode-locking method is considered to be effective, and conventionally, as shown in FIG. It is adopted in such a configuration that it is excited by a lamp 3.

Here, the resonant laser beam LAI emitted from the solid-state laser rod 1 by being excited by the excitation lamp 3 is reflected by the incident surface 4A of the output mirror 4 and is used as the excitation laser beam for the solid-state laser rod 1. The resonant laser beam LAI that is incident on the rod 1 and transmitted therethrough is reflected by the reflective surface 5A of the reflective mirror 5.

In this way, a resonator CAV is formed between the output mirror 4 and the reflection mirror 5, and the resonant laser beam LAI enters a resonant state by being repeatedly reflected between the output mirror 4 and the reflection mirror 5. The output laser beam LA2 is emitted from the output surface 4B of the output mirror 4.

The resonant frequency f of the output laser beam LA2 thus emitted
is expressed by the following equation using the distance between the incident surface 4A of the output mirror 4 and the reflective surface 5A of the reflective mirror 5, that is, the cavity length. Here C is the speed of light.

In the laser light source with such a configuration, the solid-state laser rod 1 generates laser light at other parts of the interior than the main part, so if left unattended, the laser light generated from the main part will be emitted from the output mirror 4. Laser light that becomes noise is emitted at a timing different from the timing when
In other words, a mode conflict occurs).

In the configuration shown in FIG. 3, in order to prevent such mode competition from occurring, an internal modulator controlled by the control signal S2 of the transmission control circuit 6, which is made of an acousto-optic deflection element, is provided in the optical path of the resonant laser beam LAI. 7 is provided, and this internal modulator 7 is operated at the resonance frequency fT: transmission or light blocking operation as described above for equation (1).

With this configuration □, the internal modulator 7 has a resonance frequency f
By repeatedly injecting the resonant laser beam LAI into the solid-state laser rod 1 at a period determined by (=1/f), the main part of the solid-state laser rod 1 is Among the many modes of laser light generated, only the main part of the laser light that matches the on-operation period of the internal modulator 7 is repeatedly strengthened, while the other modes of laser light generated in places other than the main part are weakened. As a result, only a laser beam having a mode matching the on-operation period of the internal modulator 7 remains as the resonant laser beam LAI between the output mirror 4 and the reflection mirror 5. Thus, the output laser beam L in the mode-locked state
A2 can be obtained, and at the same time, it is possible to avoid including noise that seems to be due to mode competition.

D Problems to be Solved by the Invention By the way, in FIG. 3, instead of the excitation lamp 3,
As shown in the figure, a method has been proposed in which the electrical efficiency of the entire laser light source is increased by using a so-called semiconductor laser excitation type solid-state laser that excites the solid-state laser bar 1 using a semiconductor laser 8 for excitation.

In FIG. 4, in which parts corresponding to those in FIG. 1, and thus a resonant laser beam LAI is generated from the solid-state laser rod 1.

According to the configuration shown in FIG. 4, the incident surface 4A of the output mirror 4 and the incident surface IA of the excitation laser beam LA3 of the solid-state laser rod 1
A cavity-length resonator CAM is formed between them, and a resonant laser beam LAI is generated in a mode-locked state by an internal modulator 7 provided inside this resonator CAM.

However, according to the configuration shown in FIG. 4, it is necessary to provide the internal modulator 7 made of a relatively expensive acousto-optic deflection element inside the resonator CAV, so the overall configuration cannot be avoided from becoming large and expensive. I don't get it.

The present invention has been made in consideration of the above points, and proposes a laser light source that can generate mode-locked output laser light with a higher efficiency with a simpler configuration than in the conventional case. This is what I am trying to do.

E Means for Solving Problem E To solve this problem, in the present invention, the laser main body 1 provided inside the resonator CAV is illuminated by the excitation laser beam LA3 emitted from the excitation semiconductor laser 8. A resonant laser beam LAI is longitudinally mode-locked to the resonator CAV by controlling the excitation semiconductor laser 8 with a modulation signal 311 having a predetermined frequency determined based on the resonant frequency f of the resonator CAV.
This resonant laser beam LAI is outputted as an output laser beam LA.
Make it fire as 2.

When the resonant laser beam LAI generated by the F-action laser body 1 travels back and forth through the cavity-length resonator CAV and returns to the laser body 1, the main part of the laser body 1 is excited by the excitation semiconductor laser 8. As a result, while the laser beams of the other modes are strengthened with the laser beam newly generated in the laser main body 1, the laser beams of other modes are not able to strengthen each other and weaken.

In this way, a laser beam in a mode having a resonant frequency f determined by the cavity length is maintained in the resonator CAV, and thus a mode-locked output laser beam LA2 can be obtained.

G example An embodiment of the present invention will be described in detail below with reference to the drawings.

(G1) In FIG. 1, in which parts corresponding to those in FIG. 4 of the first embodiment are given the same reference numerals, there is an internal No modulator is provided, and instead, the semiconductor laser 8 is driven by a modulation excitation signal 311 from a mode-locked modulation excitation circuit 21.

In the configuration shown in FIG. 1, the mode-locked modulation excitation circuit 21
is (1
) The semiconductor laser 8 is controlled on/off at the resonance frequency f described above with respect to the equation.

The solid-state laser rod 1 is intermittently driven by the excitation laser beam LA3 obtained from the semiconductor laser 8, and the solid-state laser rod 1 is intermittently excited to generate pulsed resonance. Laser light LAI is generated from the solid-state laser rod 1 toward the output mirror 4.

Here, the modulated excitation signal 3 of the mode-locked modulated excitation circuit 21
11 is selected as the resonant frequency of the resonator CAV, the resonant laser beam LAI reflected at the incident surface 4A of the output mirror 4 is transmitted to the solid-state laser rod 1.
When the excitation laser beam LA3 reaches the main part of the solid-state laser rod 1, the excitation laser beam LA3 excites the solid-state laser rod 1 at that timing.

As a result, the solid-state laser rod 1 is
The solid-state laser rod 1 can be excited so that the resonant laser beam LAI newly generated in the main part of the resonant laser beam LAI and the resonant laser beam LAI reflected on the incident surface 4A of the output mirror 4 and returned to each other strengthen each other. Only the laser beams generated in the main part of the solid-state laser rod 1 strengthen each other, while the laser beams in other modes become weaker.

In this way, a mode-locked laser beam with respect to the longitudinal mode is obtained as the output laser beam LA2, and the light intensity and frequency of this laser beam are stabilized.

According to the configuration shown in FIG. 1, in order to obtain the mode-locked output laser beam LA2, the mode-locked modulation excitation circuit 21 is
Generating means and resonator CAV for excitation laser beam LA3
By making it possible to share the mode-locking means with the mode-locking means in FIG. 3 and FIG. can be made cheaper and smaller.

According to experiments, the modulated excitation signal 311 is 1 (GHz
) When the semiconductor laser 8 was driven at a high frequency of approximately 0.15 m', a mode-locked output laser beam LA2 could be obtained from the resonator CAV with a cavity length L = 0.15 (m').

(G2) Second Embodiment FIG. 2 shows a second embodiment of the present invention. In this case, as shown by assigning the same reference numerals to corresponding parts as in FIG. A condensing lens 22 and a nonlinear optical crystal element 23 are sequentially provided on the optical path until the emitted resonant laser beam LAI is incident on the incident surface 4A of the output mirror 4, and the combined laser beam obtained from the nonlinear optical crystal element 23 is LA4 is made to enter the filter 24 through the output mirror 4, and output laser light LA2 is thus emitted from the filter 24.

Here, the nonlinear optical crystal element 23 is made of, for example, β-BaBz
Oa, and due to its nonlinear optical properties, the above-mentioned (1
) is configured to generate, based on the resonant laser beam LAI, a laser beam having a wavelength corresponding to a second harmonic having a frequency twice as high as the fundamental resonant frequency f expressed by the equation .

In the configuration shown in FIG. 2, the resonant laser beam LAI generated in the solid-state laser rod 1 by the excitation laser beam LA3 supplied from the semiconductor laser 8 to the solid-state laser rod l is directed to the nonlinear optical crystal element 23 by the condensing lens 22. As a result, the nonlinear optical crystal element 23 generates a composite laser beam LA4 containing a light component having twice the frequency.

This combined laser beam LA4 passes through the output mirror 4, and further passes through the filter 24, and is emitted as an output laser beam LA2.

Here, the combined laser beam LA4 reflected by the incident surface 4A of the output mirror 4 is reflected to the solid-state laser rod 1 through the nonlinear optical crystal element 23 and the condensing lens 22, but the main part of the solid-state laser rod l is Laser beams in modes other than the generated laser beams do not enter a resonant state where they are intensified, and thus the resonant laser beam LAI of the fundamental frequency is maintained in the resonator CA2.

According to the configuration shown in FIG. 2, the resonant laser beam LAI maintained in the resonator CAV is generated when the solid-state laser bar 1 is excited by the excitation laser beam LA3 of the semiconductor laser 8 driven by the mode-locked modulation excitation circuit 21. This results in mode locking in the same manner as described above with respect to FIG.

In such a mode-locked state, light having a wavelength having a second harmonic frequency generated in the nonlinear optical crystal element 23 passes through the output mirror 4 and the filter 24 and is emitted as a stable output laser beam LA2.

(G3) Other Embodiments (1) In the above-described embodiments, the present invention is applied to the solid-state laser bar 1 as a laser body excited by the semiconductor laser 8.
Although we have described an example in which the laser is applied to a laser light source having effect can be obtained.

(2) In the above embodiment, the modulated excitation signal 311 of the mode-locked modulated excitation circuit 21 causes the semiconductor laser 8
We have described the case where is driven at the resonant frequency f mentioned above for equation (1), but instead of this, n (n
Even if the semiconductor laser 8 is driven by a modulated excitation signal Sll having a frequency nf that is an integer), the same effect as in the above case can be obtained.

(3) In the above-described embodiment, a case has been described in which the semiconductor laser 8 is driven by a pulsed modulated excitation signal Sll, but the present invention is not limited to this. What is necessary is to drive it with a modulated excitation signal Sll having a specific wavelength.

Effects of the Invention As described above, according to the present invention, the laser body excited by the semiconductor laser is periodically excited at the resonant frequency of the resonator, so that the laser body can be adjusted to match the cavity length of the resonator. A laser light source with a simple configuration that can generate mode-locked resonant laser light and thus output laser light with stable frequency and light intensity can be easily realized.

[Brief explanation of the drawing]

FIG. 1 is a systematic diagram showing one embodiment of the laser light source according to the present invention, FIG. 2 is a systematic diagram showing another embodiment of the invention, and FIGS. 3 and 4 are conventional laser light sources. It is a route system diagram showing. 1... Solid laser rod, 3... Excitation lamp, 4... Output mirror, 5... Reflection mirror, 8...・Semiconductor laser, 9...
... Collimator, 10 ... Objective lens, 21.
...Mode-locked modulation excitation circuit.

Claims (1)

[Claims] A laser main body provided inside the resonator is excited by an excitation laser beam emitted from an excitation semiconductor laser, and the excitation semiconductor laser is heated at a predetermined frequency determined based on the resonant frequency of the resonator. A laser light source, characterized in that it generates a resonant laser beam that is longitudinally mode-locked in the resonator by controlling it with a modulation signal having a frequency of , and emits the resonant laser beam as an output laser beam.