JP4772322B2 - Laser apparatus and laser beam irradiation method - Google Patents

Description

  The present invention relates to a laser device and a laser beam irradiation method.

  The laser device is, for example, an optical communication application for generating signal light used in optical communication, a processing application for processing the processing object by irradiating the processing object with laser light, and optical recording such as an optical disk. The optical pickup is used for recording or reading data on a medium.

  In any application, the laser beam output from the laser device is irradiated to some object. In optical communication applications, laser light output from a laser device is incident on, for example, an end face of an optical fiber, and part of the incident light is reflected on the end face. In processing applications, laser light output from a laser device is irradiated onto a processing object, and part of the irradiation light is reflected or scattered by the processing object. In an optical pickup application, laser light output from a laser device is irradiated onto an optical recording medium, and part of the irradiated light is reflected or scattered by the optical recording medium. In addition, when laser light output from the laser device enters an optical system such as a lens, part of the laser light is reflected or scattered by the optical system.

  Of the laser light irradiated to the irradiation target (in the above example, the end face of the optical fiber, the processing target, the optical recording medium, or other optical system), the light reflected by the irradiation target outputs the laser light. May return to the laser device. The light that is reflected by the irradiation object and returns to the laser device is called “return light”. When such return light is present, an external resonator is constituted by any of the reflecting surfaces constituting the resonator included in the laser device and the irradiation object.

  When the external resonator is configured in this way due to the generation of return light, the wavelength of the laser light and the light output may become unstable. Further, not only noise such as pulsation and mode hopping increases in the laser device, but also the laser device may be deteriorated prematurely or cause death.

  In order to solve such a problem, an optical isolator may be provided. That is, the optical isolator allows the laser light output from the laser device to pass therethrough and blocks the return light propagating in the opposite direction. Thereby, it can suppress that return light injects into a laser apparatus, and can prevent that an external resonator is comprised. However, in general, an optical isolator has a problem that it is expensive and large.

Patent Document 1 discloses an invention of an optical isolator using elastic waves. This optical isolator generates an elastic wave that travels in the first direction. When laser light (frequency f ₀ ) is incident in the first direction, the Doppler effect causes the laser light when viewed from the diffraction grating by the elastic wave to enter. frequency _{f 1} is lower than the frequency _{f 0.} On the other hand, the frequency f ₂ of the return light from the first direction propagating in the second direction in the opposite direction is higher than the frequency f _0. Therefore, the diffraction grating using elastic waves can reflect the return light (all or part) of the frequency f ₂ while allowing the laser light of the frequency f ₁ to pass through by setting the period appropriately. . Thus, the optical isolator function can be realized by using elastic waves.
Japanese Patent No. 2809190

  However, in the optical isolator using the elastic wave as disclosed in the above-mentioned Patent Document 1, the frequency of the elastic wave needs to be approximately the same as the frequency of the laser beam, and generates such a high-frequency elastic wave. It is impossible in reality.

  The present invention has been made to solve the above problems, and can suppress the influence of the return light generated by the external resonator formed by the light source unit and the irradiation object, and can be miniaturized and easily realized. An object is to provide a laser device and a laser beam irradiation method.

  A laser apparatus according to the present invention includes a light source unit that outputs laser light, and an elastic wave generator that generates a traveling elastic wave that Bragg diffracts the laser light in a medium in a predetermined region on which the laser light output from the light source unit is incident. And a traveling elastic wave generated by the elastic wave generator when the frequency interval of the longitudinal mode of the laser beam output from the light source unit is ΔF and the full width at half maximum of the frequency spectrum of the longitudinal mode of the laser beam is Δf The frequency ω satisfies the following relational expression (1).

本発明に係るレーザ光照射方法は、照射対象物にレーザ光を照射する方法であって、弾性波発生部により進行弾性波を所定領域の媒質に発生させ、光源部から出力されたレーザ光を所定領域に入射させて進行弾性波によりブラッグ回折させ照射対象物に照射するものである。レーザ光が進行弾性波によりブラッグ回折されるに際して生じるドップラー効果により、レーザ光の周波数は弾性波周波数ωだけドップラーシフトするが、その回折させたレーザ光を照射対象物に照射するとともに、光源部が出力するレーザ光の縦モードの周波数間隔をΔＦとし、該レーザ光の縦モードの周波数スペクトルの半値全幅をΔｆとしたときに、弾性波発生部が発生する進行弾性波の周波数ωが下記(2)式の関係式を満たすことを特徴とする。また、より好適には、光源部と照射対象物とが構成する外部共振器におけるレーザ光の光子寿命時間内での当該光子の往復可能回数をＮとしたときに、弾性波発生部が発生する進行弾性波の周波数ωが下記(3)式の関係式を満たす。

A laser light irradiation method according to the present invention is a method of irradiating an irradiation object with laser light, wherein a traveling elastic wave is generated in a medium in a predetermined region by an elastic wave generating unit, and laser light output from a light source unit is emitted. It is incident on a predetermined region and Bragg diffracted by a traveling elastic wave to irradiate an irradiation object. Due to the Doppler effect that occurs when the laser light is Bragg diffracted by the traveling elastic wave, the frequency of the laser light is Doppler shifted by the elastic wave frequency ω, and the object to be irradiated is irradiated with the diffracted laser light. When the frequency interval of the longitudinal mode of the laser beam to be output is ΔF and the full width at half maximum of the frequency spectrum of the longitudinal mode of the laser beam is Δf, the frequency ω of the traveling elastic wave generated by the elastic wave generating unit is (2 It is characterized by satisfying the relational expression of). More preferably, the elastic wave generating unit is generated when the number of reciprocations of the photon within the photon lifetime of the laser beam in the external resonator formed by the light source unit and the irradiation target is N. The frequency ω of the traveling elastic wave satisfies the relational expression (3) below.

光源部、弾性波発生部および所定領域が共通の基板上に設けられているのが好適である。また、光源部が半導体レーザ素子を含むのも好適である。

It is preferable that the light source unit, the elastic wave generating unit, and the predetermined region are provided on a common substrate. It is also preferable that the light source unit includes a semiconductor laser element.

  According to the present invention, laser light is output from the light source unit, and a diffraction grating due to traveling elastic waves is generated in the elastic wave propagation medium in a predetermined region by the elastic wave generating unit. The laser beam is Bragg diffracted by the diffraction grating, and the irradiation target is irradiated with the laser light after the Bragg diffraction. When the irradiation target is irradiated with the laser light, the laser light is reflected or scattered by the irradiation target and is Bragg diffracted again by the traveling elastic wave. The laser light after this Bragg diffraction may return to the light source unit. is there. However, when the above relational expression is satisfied, oscillation in the external resonator formed by the light source unit and the irradiation target is suppressed, and the influence of return light is suppressed.

  The laser device and the laser beam irradiation method according to the present invention can suppress the influence of the return light to the light source, can be miniaturized, and can be easily realized.

  The best mode for carrying out the present invention will be described below in detail with reference to the accompanying drawings. In the description of the drawings, the same elements are denoted by the same reference numerals, and redundant description is omitted.

  FIG. 1 is a conceptual diagram illustrating a laser device and a laser beam irradiation method according to the present embodiment. The laser device 1 according to the present embodiment irradiates the irradiation object 2 with laser light, and includes a light source unit 10, an elastic wave generation unit 20, and an elastic wave propagation medium 30. The light source unit 10, the elastic wave generating unit 20, and the elastic wave propagation medium 30 are preferably provided monolithically on a common substrate.

The light source unit 10 and outputs a laser beam L _0. The light source unit 10 may be a semiconductor laser, a glass laser, or another laser light source. The light source unit 10 is preferably a distributed feedback semiconductor laser.

The elastic wave generating unit 20 generates a traveling elastic wave in the elastic wave propagation medium 30 and is provided in the elastic wave propagation medium 30. For example, the elastic wave generating unit 20 has a configuration in which a pair of comb-shaped electrodes are combined as shown in the figure, and the laser light L in the elastic wave propagation medium 30 is applied by applying an AC voltage between the electrodes. _An elastic wave is generated in a region where ₀ is incident. The elastic wave generated in the elastic wave propagation medium 30 by the elastic wave generator 20 is a traveling wave, and acts as a diffraction grating 40 that Bragg diffracts the laser light L ₀ output from the light source unit 10. The direction of traveling elastic waves is arbitrary as long as the diffraction grating 40 to the laser beam L ₀ is the Bragg diffraction is formed.

The Bragg diffraction condition is expressed by the following equation (4). Here, Λ is the grating period of the diffraction grating 40 by traveling elastic waves. θ is an angle formed by the laser beam and the traveling direction of the traveling elastic wave (see FIG. 1). l is the diffraction order. λ is the laser wavelength. N _a is the refractive index of the elastic wave propagation medium 30.

また、弾性波発生部２０により弾性波伝播媒質３０において生じた進行弾性波による回折格子４０については、下記(5)式の関係式がある。ここで、ｖ_ｕは弾性波伝播媒質３０における進行弾性波の伝播速度である。また、ωは進行弾性波の周波数である。

The diffraction grating 40 by the traveling elastic wave generated in the elastic wave propagation medium 30 by the elastic wave generating unit 20 has the following relational expression (5). Here, v _u is the propagation velocity of the traveling elastic wave in the elastic wave propagation medium 30. Ω is the frequency of the traveling elastic wave.

また、光源部１０から出力されたレーザ光については、下記(6)式の関係式がある。ここで、ｃは光速であり、Ωはレーザ光の周波数である。

The laser beam output from the light source unit 10 has the following relational expression (6). Here, c is the speed of light, and Ω is the frequency of the laser beam.

上記(5)式および(6)式を用いると、上記(4)式は下記(7)式に変形される。

Using the above formulas (5) and (6), the above formula (4) is transformed into the following formula (7).

このレーザ装置１では、光源部１０からレーザ光Ｌ_０が出力され、また、弾性波発生部２０により弾性波伝播媒質３０において進行弾性波による回折格子４０が生じる。そして、この回折格子４０によりレーザ光Ｌ_０がブラッグ回折されて、このブラッグ回折した後のレーザ光Ｌ_１が照射対象物２に照射される。レーザ光Ｌ_１が照射対象物２に照射されると、そのレーザ光Ｌ_１は、照射対象物２において反射または散乱されて回折格子４０により再びブラッグ回折され、このブラッグ回折した後のレーザ光Ｌ_２が光源部１０に戻る場合がある。

In the laser device 1, the laser light L ₀ is output from the light source unit 10, and the diffraction grating 40 due to the traveling elastic wave is generated in the elastic wave propagation medium 30 by the elastic wave generating unit 20. Then, the laser beam L ₀ is Bragg diffracted by the diffraction grating 40, and the irradiation target object 2 is irradiated with the laser light L ₁ after the Bragg diffraction. When the laser beam L ₁ is irradiated to the irradiation target object 2, the laser beam L ₁ is again Bragg diffracted by the diffraction grating 40 is reflected or scattered in the irradiation target object 2, the laser beam L after the Bragg diffraction ₂ may return to the light source unit 10.

Further, when the laser beam L ₂ is reflected by the light source unit 10, the reflected laser beam L ₂ is Bragg diffracted by the diffraction grating 40, and the laser beam L ₃ after the Bragg diffraction is irradiated on the irradiation object 2. In some cases, the laser beam L ₄ is reflected or scattered and is Bragg diffracted again by the diffraction grating 40, and the laser light L ₄ after the Bragg diffraction returns to the light source unit 10. Thus, the light source unit 10 and the irradiation object 2 may constitute an external resonator.

In this description and FIG. 1, the laser light L ₀ indicates the light that is first output from the light source unit 10 and is incident on the diffraction grating 40 for the first time. The laser beam L _2m−1 indicates a laser beam that is reflected by the irradiation object 2 and incident on the diffraction grating 40 again after the (2m−1) th diffraction by the diffraction grating 40. The laser beam L _2m indicates a laser beam reflected by the light source unit 10 after being diffracted for the second time by the diffraction grating 40 and entering the diffraction grating 40 again. m is an arbitrary integer of 1 or more.

  In the present embodiment, the frequency interval of the longitudinal mode of the laser beam output from the light source unit 10 is ΔF, the full width at half maximum of the frequency spectrum of the longitudinal mode of the laser beam is Δf, and the light source unit 10 and the irradiation object 2 are configured. Let N be the number of times the photon can reciprocate within the photon lifetime of the laser light in the external resonator. At this time, the frequency ω of the traveling elastic wave generated by the elastic wave generating unit 20 in the elastic wave propagation medium 30 satisfies the following expression (8), and more preferably satisfies the following expression (9).

本実施形態に係るレーザ光源１およびレーザ光照射方法では、上記(8)式（好適には上記(9)式）の関係式が満たされていることにより、光源部１０と照射対象物２とが構成する外部共振器における発振が抑制される。このことについて以下に詳細に説明する。

In the laser light source 1 and the laser light irradiation method according to the present embodiment, the relational expression of the above expression (8) (preferably the above expression (9)) is satisfied. Oscillation in the external resonator constituted by is suppressed. This will be described in detail below.

FIG. 2 is a diagram illustrating a frequency spectrum of laser light and the like in the laser apparatus and laser light irradiation method according to the present embodiment. The light source unit 10 can oscillate in a longitudinal mode having discrete frequencies Ω _{1 to} Ω ₃ according to the resonator length and the like. The laser beam L ₀ of the frequency Omega output from the light source unit 10 is a laser beam L ₁ of a frequency (Ω + ω) by the Doppler effect after being Bragg diffracted by the diffraction grating 40. Further, the laser beam L ₁ is the laser light L ₂ of the frequency (Ω + 2ω) is after being Bragg diffraction by again the diffraction grating 40 are reflected by the irradiated object 2. In general, the laser beam L _2m that returns to the light source unit 10 by the Doppler effect after reciprocating between the light source unit 10 and the irradiation object 2 m times is subjected to Doppler shift by Bragg diffraction of 2 m times by the diffraction grating 40. The frequency becomes (Ω + 2 mΩ).

  As shown in FIG. 2A, when the frequency shift amount of the laser beam returning to the light source unit 10 is smaller than the full width at half maximum of the frequency spectrum of the laser beam, the laser beam returning to the light source unit 10 Since the laser beam newly emitted from the unit 10 and the frequency component overlap, an external resonator may be formed and oscillation may occur. Further, as shown in FIG. 2B, when the frequency of the laser light returning to the light source unit 10 is equal to the frequency of the other longitudinal mode of the light source unit 10, a laser newly emitted from the light source unit 10. There is a possibility that the frequency mode of light overlaps and an external resonator is formed, causing oscillation. In these cases, since the external resonator is formed between the light source unit 10 and the object, the return light is likely to affect the laser light source.

  On the other hand, as shown in FIG. 2C, when the frequency shift amount (2ω) of the laser beam returning to the light source unit 10 satisfies the relational expression (8), the laser beam returns to the light source unit 10. Since the frequency component differs from the laser beam newly emitted from the light source unit 10, oscillation does not occur in the external resonator. Further, considering the laser light returning to the light source unit 10 after reciprocating between the light source unit 10 and the irradiation object 2 N times, since the frequency shift amount is 2Nω, the above equation (9) is satisfied. In this case, the laser light that has returned to the light source unit 10 does not overlap the frequency component of the laser light that is newly emitted from the light source unit 10, and oscillation does not occur in the external resonator.

Note that the full width at half maximum Δf of the frequency spectrum of the longitudinal mode of the laser light is expressed by the following Shallow Towns equation (10). Here, h is a Planck constant. ω ₀ is the center frequency. γ is “(rate of induced release + rate of induced absorption) / (rate of induced release−rate of induced absorption)”. v is the medium velocity. g ₀ is a gain coefficient. R is the resonance surface reflectance. P ₀ is the optical output power. L is the resonator length. Α is the influence of a change in refractive index due to carrier density fluctuation.

また、光源部１０が出力するレーザ光の縦モードの周波数間隔ΔＦは、下記(11)式で表される。ここで、ｎ_ｒは波長分散を考慮した屈折率である。

Further, the frequency interval ΔF in the longitudinal mode of the laser light output from the light source unit 10 is expressed by the following equation (11). Here, _nr is a refractive index considering wavelength dispersion.

次に、光源部１０と照射対象物２とが構成する外部共振器におけるレーザ光の光子寿命時間内での当該光子の往復可能回数Ｎについて説明する。図３は、本実施形態に係るレーザ装置およびレーザ光照射方法における光子の往復可能回数Ｎについて説明するための図である。同図に示されるように、光源部１０のファブリ・ペロー型の共振器を構成する２つの反射面のうち、高い反射率で光を反射させる反射面１１の反射率をｒ_０とし、一部を反射させ残部を外部へ出射する出射面１２の反射率をｒ_１とする。照射対象物２の反射率をｒ_２とする。また、回折格子４０におけるブラッグ回折時の反射率をｒ_ａとする。なお、ここでは、光路中での損失については無視する。

Next, the number N of possible reciprocations of the photon within the photon lifetime of the laser light in the external resonator formed by the light source unit 10 and the irradiation object 2 will be described. FIG. 3 is a diagram for explaining the reciprocable number N of photons in the laser apparatus and laser light irradiation method according to the present embodiment. As shown in the figure, of the two reflecting surfaces constituting the Fabry-Perot resonator of the light source unit 10, the reflectance of the reflecting surface 11 that reflects light with a high reflectance is r ₀ , and a part thereof The reflectance of the emission surface 12 that reflects the light and emits the remainder to the outside is denoted by r ₁ . The reflectivity of the irradiated object 2 and r _2. Also, the reflectivity at the Bragg diffraction in the diffraction grating 40 and r _a. Here, the loss in the optical path is ignored.

In the optical system as shown in the figure, two types of resonance can be considered as external resonators. The first resonance is a resonance between the emission surface 12 (reflectance r ₁ ) of the light source unit 10 and the irradiation object 2 (reflectance r ₂ ), and the second resonance is the light source unit 10 (effective Resonance between the reflectivity r _e ) and the irradiation object 2 (reflectance r ₂ ). In the case of the second resonance, the effective reflectivity r _e of the light source 10, the reflectance of the entire light source unit 10 in consideration of the gain and loss in the light source unit 10..

Effective reflectivity r _e of the light source section 10 is expressed by the following equation (12). Here, g is a gain in the light source unit 10, and α is a loss in the light source unit 10. Further, the laser oscillation condition in the light source unit 10 is expressed by the following equation (13). Using this equation (13), (12) the effective reflectivity r _e of the equation is transformed into the following equation (14).

このことから、光源部１０の出射面１２の反射率ｒ_１が光源部１０の実効的反射率ｒ_ｅより大きい場合には、光源部１０の出射面１２での反射（反射率ｒ_１）による外部共振器を考える。一方、光源部１０の出射面１２の反射率ｒ_１が光源部１０の実効的反射率ｒ_ｅより小さい場合には、光源部１０での実効的な反射（反射率ｒ_ｅ）による外部共振器を考える。

From this, when the reflectance r ₁ of the emission surface 12 of the light source unit 10 is larger than the effective reflectance r _e of the light source unit 10, it is due to reflection (reflection rate r ₁ ) on the emission surface 12 of the light source unit 10. Consider an external resonator. On the other hand, when the reflectance r ₁ of the emission surface 12 of the light source unit 10 is smaller than the effective reflectance r _e of the light source unit 10, an external resonator due to effective reflection (reflectance r _e ) at the light source unit 10. think of.

When the reflectivity r ₁ of the emission surface 12 of the light source unit 10 is larger than the effective reflectivity r _{e of} the light source unit 10, the photon within the photon lifetime of the laser beam in the external resonator by the emission surface 12 of the light source unit 10. The reciprocable number of times N is expressed by the following equation (15). Here, τ _p is the photon lifetime, and t is the time for the photon to make one round trip through the external resonator. When this is modified, the following equation (16) is obtained.

一方、光源部１０の出射面１２の反射率ｒ_１が光源部１０の実効的反射率ｒ_ｅより小さい場合、光源部１０での実効的な反射（反射率ｒ_ｅ）による外部共振器におけるレーザ光の光子寿命時間内での当該光子の往復可能回数Ｎは、下記(17)式で表される。これを変形すると、下記(18)式が得られる。

On the other hand, when the reflectance r ₁ of the emission surface 12 of the light source unit 10 is smaller than the effective reflectance r _{e of} the light source unit 10, the laser in the external resonator due to the effective reflection (reflectance r _e ) at the light source unit 10. The number of reciprocations N of the photon within the photon lifetime of light is expressed by the following equation (17). When this is modified, the following equation (18) is obtained.

次に、光源部１０が半導体レーザ素子である場合の具体的数値例について説明する。ここでは、半導体レーザ素子として一般的であるＡｌＧａＡｓ系の出力波長８００ｎｍ帯の半導体レーザ素子を例に挙げる。「（誘導放出の割合＋誘導吸収の割合）/（誘導放出の割合−誘導吸収の割合）」を表すγは４であり、利得係数ｇ_０は１００ｃｍ^−１であり、媒質速度ｖは１０^８ｍ／ｓｅｃであり、共振面反射率Ｒは０.３であり、光出力パワーＰ_０は１０ｍＷであり、共振器長Ｌは０.５ｍｍであり、キャリア密度ゆらぎによる屈折率変化の影響αは５.４であり、屈折率ｎ_ｒが３.６であるとする。

Next, specific numerical examples when the light source unit 10 is a semiconductor laser element will be described. Here, an AlGaAs-based semiconductor laser device having an output wavelength band of 800 nm, which is a general semiconductor laser device, is taken as an example. Γ representing “(rate of induced emission + rate of induced absorption) / (rate of induced emission−rate of induced absorption)” is 4, the gain coefficient g ₀ is 100 cm ⁻¹ , and the medium velocity v is 10 ^8. m / sec, the resonant surface reflectance R is 0.3, the optical output power P ₀ is 10 mW, the resonator length L is 0.5 mm, and the influence α of the refractive index change due to the carrier density fluctuation is α. It is assumed that the refractive index n _r is 5.4 and the refractive index n _r is 3.6.

  At this time, when calculated using the above equation (10), the spectral line width Δf of the semiconductor laser element is 14 MHz. The above Δf value is comparable to the values reported by various papers and is reasonable. Further, when calculated using the above equation (11), the mode interval ΔF of the semiconductor laser element is 83 GHz.

Further, the reflectance r ₀ of the reflecting surface 11 of the semiconductor laser element is set to 90%, and the reflectance r ₁ of the emitting surface 12 is set to 10%. The reflectivity _{r 2} of the irradiation target object 2 and 10%, the reflectance _{r a} at the Bragg diffraction at the diffraction grating 40 to 90%. At this time, as calculated using the above expression (14), since the effective reflectivity r _e of the light source 10 is 8.1, the effective reflectivity r ₁ of the emission surface 12 of the light source unit 10 of the light source unit 10 is smaller than the reflectance r _e, it is necessary to consider the external resonator according to the effective reflection in the light source unit 10 (reflectance r _e). When calculated using the above equation (18), the number of reciprocations N of the photon within the photon lifetime of the laser beam in the external resonator is 2.3.

  When these parameter values are substituted into the above equation (9), the allowable numerical value range of the frequency ω of the traveling elastic wave is 7 MHz to 36 GHz. In this way, a traveling elastic wave in a very wide frequency range is allowed, but since the propagation loss of the traveling elastic wave is proportional to the square of the elastic wave frequency, it is actually easy to obtain the traveling elastic wave and the propagation loss is small. A traveling elastic wave having a frequency of about 100 MHz to 1 GHz may be used.

Next, specific numerical examples when the light source unit 10 is a glass laser light source will be described. Here, an Nd-doped glass laser is considered. When the spectral line width Δf of the glass laser light source is considered in comparison with the semiconductor laser element, the gain coefficient g ₀ is small, and the resonator length L and the optical output power P ₀ are very large values. Therefore, from the above equation (10), Δf of the glass laser light source is very small as compared with the semiconductor laser element, but in reality, the spectral line width Δf of the glass laser light source is influenced by quantum noise and the like. For this reason, since it becomes larger than the theoretical value, it is assumed here that a value equivalent to that of the semiconductor laser element is simply taken. Further, assuming that the oscillation wavelength λ ₀ is 1060 nm, the refractive index n _r is 1.5, and the resonator length L is 10 cm, the mode interval ΔF of the glass laser light source is 1 GHz when calculated using the above equation (11). Become.

Further, the reflectance r ₀ of the reflecting surface 11 of the glass laser light source is set to 100%, and the reflectance r ₁ of the emitting surface 12 is set to 95%. The reflectivity _{r 2} of the irradiated object 2 was 90%, the reflectance _{r a} at the Bragg diffraction at the diffraction grating 40 to 90%. At this time, as calculated using the above expression (14), since the effective reflectivity r _e of the light source 10 is 0.002, the effective reflectivity r ₁ of the emission surface 12 of the light source unit 10 of the light source unit 10 is greater than the reflectance r _e, it is necessary to consider the external resonator according to the emission surface 12 of the light source unit 10. When calculated using the above equation (16), the number of reciprocations N of the photon within the photon lifetime of the laser beam in the external resonator is 2.7.

  When these parameter values are substituted into the above equation (9), the allowable numerical range of the frequency ω of the traveling elastic wave is 7 MHz to 183 MHz. A traveling elastic wave in such a frequency range has a small propagation loss and can be easily obtained.

  Next, a specific configuration example of the laser apparatus 1 according to the present embodiment will be described with reference to FIG. The laser device 1 shown in the figure has an AlGaAs-based semiconductor laser light source having an output wavelength band of 800 nm used for derivation of the above-described acoustic wave frequency condition as a light source unit 10. The unit 20 and the elastic wave propagation medium 30 are monolithically provided on the common substrate 51. Further, the ZnO layer 58, the elastic wave generating unit 20, and the light source unit 10 are provided to be separated from each other by the groove 61.

  On one main surface of the n-type GaAs substrate 51, an n-type AlGaAs cladding layer 52, an AlGaAs quantum well active layer 53, a p-type AlGaAs cladding layer 54, and a p-type GaAs contact layer 55 are provided in this order. The n-type AlGaAs cladding layer 52 has, for example, an Al composition of 30% and a thickness of 1.5 μm. The p-type AlGaAs cladding layer 54 has, for example, an Al composition of 30% and a thickness of 1.5 μm. The p-type GaAs contact layer 55 has a thickness of 0.1 μm, for example. An AuGe / Au electrode 59 is provided on the back surface of the n-type GaAs substrate 51.

  In the light source unit 10, a SiN insulating layer 56 and a Cr / Au electrode 57 are provided on the p-type GaAs contact layer 55. In a partial region on the p-type GaAs contact layer 55, the SiN insulating layer 56 is not provided, and the Cr / Au electrode 57 is electrically connected to the p-type GaAs contact layer 55.

  On the opposite side of the light source unit 10 with the groove 61 therebetween, a ZnO layer 58 and an elastic wave generating unit 20 are provided. The elastic wave generator 20 has a pair of comb-shaped electrodes meshed with each other, and a ZnO layer 58 is provided below the elastic wave generator 20 and in a limited region around the periphery. The groove 61 reaches the n-type AlGaAs cladding layer 52. The side wall surface of the groove 61 on the light source unit 10 side is the emission surface 12.

In this laser device 1, when a drive current is supplied between the electrode 57 and the electrode 59 of the light source unit 10, laser light is generated in the quantum well active layer 53 of the light source unit 10. The laser light is emitted from the emission surface 12 to the groove 61 and is incident on the quantum well active layer 53 below the ZnO layer 58. The incident laser light L ₀ is guided in the quantum well active layer 53 and is Bragg diffracted by the diffraction grating 40 by the traveling elastic wave generated by the elastic wave generating unit 20. Then, the laser light L ₁ after the Bragg diffraction is emitted from the end face 62 to the outside.

  Next, a manufacturing method of the laser apparatus according to the present embodiment shown in FIG. 4 will be described with reference to FIG. First, a semiconductor epitaxial growth substrate is prepared. That is, an n-type GaAs substrate 51 is prepared, and an n-type AlGaAs cladding layer 52, an AlGaAs quantum well active layer 53, a p-type AlGaAs cladding layer 54, and a p-type GaAs contact layer 55 are sequentially formed thereon by epitaxial growth. (See FIG. 5A). At this time, the composition and thickness of each layer are as described above.

  Subsequently, the SiN insulating layer 56 is deposited on the entire upper surface of the semiconductor epitaxial growth substrate, and then the SiN insulating layer 56 is selectively removed by photowork and etching in the electrode 57 and the elastic wave propagation medium portion 30 to form the light source portion. 10, a p-side Cr / Au electrode 57 is formed by vapor deposition. And the groove | channel 61 is formed by the vertical etching by a photowork and RIE method (refer FIG.5 (b)).

Subsequently, a ZnO layer 58, which is a piezoelectric material, is formed on the opposite side of the light source unit 10 with the groove 61 therebetween, and an Al electrode is deposited on the ZnO layer 58, thereby generating an elastic wave generating unit. 20 is formed. At this time, the elastic wave generating unit 20 needs to be arranged so that the traveling direction of the traveling elastic wave is an angle that matches the Bragg diffraction condition described above. For example, the diffraction order is 1, a 500MHz true acoustic wave frequency ω in the elastic wave frequency condition of the semiconductor laser light source described above, the medium velocity v _u and 3 × 10 3 ^{m /} s, a medium refractive index n _a 3 When the laser beam frequency Ω is 3.78 × 10 ¹⁴ Hz, the crossing angle θ between the laser beam and the traveling direction of the traveling elastic wave is set to 1.11 ° according to the Bragg diffraction condition described above. Thereafter, the back surface of the substrate 51 is polished, and an AuGe / Au electrode 59 is deposited on the back surface as an n-side electrode, and further annealed to alloy the vicinity of the interface between the electrode 59 and the substrate 51 (FIG. 5). (See (c)).

  Finally, the side wall of the element is opened to form a mirror surface, and a desired reflective coating film is formed on the mirror surface, and the semiconductor laser light source 1 as shown in FIG. 4 is manufactured.

  As described above in detail, in the laser light source and laser light irradiation method according to the present embodiment, the light source unit is satisfied by satisfying the relational expression (8) above (preferably the above (9)). The influence of the return light caused by oscillation in the external resonator formed by the object 10 and the irradiation object 2 is suppressed, and can be miniaturized and easily realized. As a result, the wavelength of the laser beam becomes stable, noise generation such as pulsation and mode hopping and element deterioration are suppressed in the semiconductor laser element used as the light source unit, and deterioration of the semiconductor laser element is suppressed. The

The present invention is not limited to the above embodiment, and various modifications can be made. For example, it is good also as a structure as shown in FIG. 6 or FIG. If these described arrangement is advantageous since the light L ₁ perpendicularly from the element end face is emitted.

FIG. 6 is a plan view showing a first modification of the laser apparatus according to the present embodiment. The laser device 1A of the first modified example shown in this figure is different from the laser device 1 already described with reference to FIGS. 4 and 5 in that a groove 62 is provided. The groove 62 reaches the n-type AlGaAs cladding layer 52 and can be formed by the same method as the formation of the groove 61. Then, the groove portion 62, the light L ₁ which is Bragg diffracted by the diffraction grating 40 by traveling acoustic wave generated by the elastic wave generating unit 20 is reflected by the sidewall surface, emit vertically the light that is reflected from the element end face .

FIG. 7 is a plan view showing a second modification of the laser apparatus according to the present embodiment. Compared with the configuration of the laser device 1A described with reference to FIG. 6, the laser device 1B of the second modification shown in this figure is that the elastic wave generating unit 20B is provided on the element side wall, and the groove 63 and the groove 64 in that the light source unit 10 is formed between the light source unit 64 and the optical axis of the resonator of the light source unit 10 is inclined with respect to the element side wall. Each of the groove 63 and the groove 64 reaches the n-type AlGaAs cladding layer 52, and each side wall surface constitutes a resonator of the light source unit 10. The elastic wave generator 20B provided on the side wall of the element has a metal film 21, a piezoelectric film 22 and a metal film 23 stacked in this order on the side wall via an insulating film 70. For example, the insulating film 70 is made of SiO ₂ or SiN, the piezoelectric film 22 is made of ZnO, and the metal films 21 and 22 are made of Au. These can be formed by vapor deposition or sputtering.

In this laser apparatus 1B, a traveling elastic wave that travels perpendicular to the element side wall is generated by applying a high-frequency voltage between the metal film 21 and the metal film 22. The light L ₀ output from the light source unit 10 proceeds while being inclined with respect to the element side wall, and is Bragg diffracted by the diffraction grating 40 due to the traveling elastic wave generated by the elastic wave generating unit 20B. The light L ₁ after Bragg diffraction is reflected by the sidewall surface of the groove 62, is emitted perpendicularly from the device end face.

It is a conceptual diagram explaining the laser apparatus and laser beam irradiation method which concern on this embodiment. It is a figure which shows the frequency spectrum etc. of the laser beam in the laser apparatus and laser beam irradiation method which concern on this embodiment. It is a figure for demonstrating the frequency | count N of the reciprocation of a photon in the laser apparatus and laser beam irradiation method which concern on this embodiment. It is a perspective view which shows the specific structure of the laser apparatus concerning this embodiment. It is process drawing explaining the manufacturing method of the laser apparatus concerning this embodiment. It is a top view which shows the 1st modification of the laser apparatus which concerns on this embodiment. It is a top view which shows the 2nd modification of the laser apparatus which concerns on this embodiment.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1,1A, 1B ... Laser apparatus, 2 ... Irradiation target object, 10 ... Light source part, 20, 20B ... Elastic wave generation part, 30 ... Elastic wave propagation medium, 40 ... Diffraction grating.

Claims (7)

A light source unit that outputs a laser beam, and an elastic wave generator that generates a traveling elastic wave that Bragg diffracts the laser beam in a medium in a predetermined region on which the laser beam output from the light source unit is incident,
The frequency of the traveling elastic wave generated by the elastic wave generator when the frequency interval of the longitudinal mode of the laser beam output from the light source unit is ΔF and the full width at half maximum of the frequency spectrum of the longitudinal mode of the laser beam is Δf. ω is

Satisfying the relational expression
A laser device characterized by that.   The laser device according to claim 1, wherein the light source unit, the elastic wave generating unit, and the predetermined region are provided on a common substrate.   The laser device according to claim 1, wherein the light source unit includes a semiconductor laser element. A method of irradiating an irradiation object with laser light,
A traveling elastic wave is generated in a medium in a predetermined region by an elastic wave generating unit, laser light output from a light source unit is incident on the predetermined region, Bragg diffracted by the traveling elastic wave, and the diffracted laser light is While irradiating the irradiation object,
The frequency of the traveling elastic wave generated by the elastic wave generator when the frequency interval of the longitudinal mode of the laser beam output from the light source unit is ΔF and the full width at half maximum of the frequency spectrum of the longitudinal mode of the laser beam is Δf. ω is

Satisfying the relational expression
And a laser beam irradiation method. A traveling elastic wave generated by the elastic wave generator when the number of reciprocations of the photon within the photon lifetime of the laser light in the external resonator formed by the light source unit and the irradiation object is N. The frequency ω of

The laser beam irradiation method according to claim 4, wherein the following relational expression is satisfied.   The laser light irradiation method according to claim 4, wherein the light source unit, the elastic wave generation unit, and the predetermined region are provided on a common substrate. The laser light irradiation method according to claim 4, wherein the light source unit includes a semiconductor laser element.

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