JPH0453572Y2 - - Google Patents

Description

[Detailed description of the invention] (Field of industrial application) This invention is applicable to measurement devices, especially measurement devices using the CARS method, which uses pump light ω ₁ and Stokes light ω ₂ produced by dye laser light as the incident light source. The present invention relates to a dye laser device for obtaining CARS signal light (anti-Stokes light) ω ₃ with high efficiency and high S/N ratio.

(Prior Art) There are mainly two types of dye laser devices conventionally used in CARS measuring devices:

FIGS. 2 and 3 are explanatory diagrams for explaining a conventional dye laser device.

In the dye laser device shown in FIG. 2, the intensity distribution of the beam cross-sectional shape (pattern) of the excitation laser beam L ₁ used as the excitation light source can be regarded as a Gaussian distribution, and therefore the pattern P ₁ can be regarded as circular.
This circular pattern of excitation laser light _L1 is focused by a suitable spherical lens 10 to excite the dye laser,
Dye laser light (Stokes light) is obtained as output light _L2 .

The dye laser mainly includes a dye cell 12, a total reflection mirror 14, and an output mirror 16.
In order to prevent reflection loss on the surface of the dye cell 12, the excitation laser beam _L1 is normally incident on the dye cell 12 at the Brewster angle θ, and the dye has a pattern _P1 whose cross-sectional shape can be regarded as a center-symmetric circular shape. It is configured to oscillate laser _L1 .

In the dye laser device shown in FIG. 3, a beam having a rectangular cross-sectional shape _P2 as excitation laser light _L1 is condensed and excited from a direction perpendicular to the optical axis of the dye laser by a cylindrical lens 18. Circular pattern P ₁ that can be considered a circular shape with central symmetry
The structure is such that it oscillates the dye laser light as output light _L2 . In this case, an antireflection film coating may be provided to prevent reflection on the surface of the dye cell 12.

(Problem that the invention attempts to solve) However, the fact that the cross-sectional pattern of the dye laser L ₂ is circular in this way means that the cross-sectional shape of the Stokes light ω ₂ that irradiates the sample is a circular pattern. It is. Furthermore, the cross-sectional shape of the pump light ω ₁ that irradiates the sample together with this Stokes light ω ₂ also has a circular pattern. The energy distribution of these two lights ω ₁ and ω ₂ is usually a spatially centrally symmetric TEM ₀ Gaussian distribution or a near Gaussian mode laser beam, so when the two lights ω ₁ and ω ₂ are combined, The laser light incident on the sample is already coupled over a fairly wide area extending outside the area of the sample. Therefore, since the incident laser beam has strong intensity even in areas other than the sample, undesired CARS light is generated as a noise signal from the optical element, such as the glass window of the sample container, and the spatial resolution of the CARS light is low. (Positional resolution) was poor, and furthermore, it was necessary to adjust the intensity ratio of the pump light ω ₁ and the Stokes light ω ₂ using an optical attenuator specially provided in the optical path.

In view of these conventional problems, the purpose of this invention is to provide a dye laser device configured so that noisy CARS light is not generated.

(Means for Solving the Problem) In order to achieve this purpose, according to the dye laser device of this invention, the incident optical system has a cross-sectional pattern of the excitation laser beam that can be regarded as a circular shape, and a half-moon shape and a half-moon shape, respectively. It is equipped with an optical element that splits the beam into two beams with a cross-sectional pattern that can be considered as half-moon, and one of the split beams that can be seen as half-moon-shaped is made incident at an acute angle to the optical axis of the dye laser to excite the dye laser, thereby creating a half-moon shape. It is characterized by arranging this dye laser so that it oscillates with an output light that can be regarded as .

(Function) With this configuration, the excitation laser beam can be split into two beams with the same half-moon shape pattern using the optical element, and one of the split beams can be used to excite the dye laser to form a half-moon shape. Since it is possible to oscillate a dye laser with a cross-sectional pattern, by appropriately adjusting the optical system leading to the sample, both the pump light and Stokes light patterns can be separated independently from each other until they are incident on the sample. The patterns of both lights can be combined only within the sample area without overlapping.

By doing this, the spatial resolution is increased, and since the light intensity is weak in areas other than the sample, CARS light is not generated from other objects, and therefore noise is not generated.

(Embodiments) Hereinafter, embodiments of this invention will be described with reference to the drawings.

FIG. 1 is a schematic diagram showing the structure of the dye laser device of this invention. In the figure, the same components as those of the conventional device are denoted by the same reference numerals.
A detailed explanation thereof will be omitted.

First, in this invention, an optical element such as a prism beam splitter is used in the input optical system of the dye laser, which can split the excitation laser beam L ₁ with a circular pattern P ₁ into two beams with equal half-moon patterns P ₃ and P ₄ . 20 are provided. One of the divided beams
The energy intensity distribution of the other beam, which becomes L ₃ and pump light ω ₁ , is also divided into intensity distributions corresponding to these beam patterns. This beam L ₃ is used to maintain this half-moon-shaped pattern P ₅ using an appropriate lens 22, and the dye cell 12 is irradiated at an acute angle of incidence with respect to the optical axis of the dye laser to excite the dye. The cross-sectional shape of the oscillating laser (output light) _L2 within the laser becomes a half-moon-shaped pattern _P6 , and therefore the cross-sectional shape of the oscillating laser _L2 also becomes a half-moon shape, that is, a semicircular pattern _P7 .

Therefore, when the oscillation laser L ₂ is used as the Stokes light ω ₂ , the cross-sectional shapes of both the pump light ω ₁ and the Stokes light ω ₂ for irradiating the sample become a half-moon pattern. In this case, since we originally divided one circular pattern into two,
Both the pump light and Stokes light patterns correspond to each of the semicircular patterns forming the two-part circular pattern.

The sample is irradiated with the pump light ω ₁ thus obtained and the Stokes light ω ₂ as the oscillated dye laser L ₂ .

In this case, the pump light ω ₁ and the Stokes light ω ₂ are combined using a suitable optical system so that they overlap each other only within the sample.

This method of overlapping will be explained. As already explained, the light intensity is usually maximum at the center of the cross-sectional pattern of the incident laser. For example, since the beam from a YAG laser has a circular cross-section, the light intensity is high at the center of the circular cross-section and becomes weaker toward the periphery. Therefore, the excitation laser beam L ₁ is equally divided at the center of the circular cross section by the optical element 20 to form half-moon-shaped patterns P ₃ and P ₄ , respectively, and the energy intensity distribution is also divided into two. Then, the obtained pump light ω ₁ and the Stokes light ω ₂ as an oscillation laser are made to overlap only within the sample region. In this way, the sample can be irradiated with a beam whose energy is approximately evenly distributed within the cross-sectional pattern and whose intensity is weaker than that of the incident beam.

Therefore, spatial resolution is improved, and CARS light is not generated from anything other than the sample, so noise is not generated.

In the above embodiment, a prism was used as an example of an optical element. However, it is also possible to use an optical element other than a prism, which has the function of dividing a cross-sectional pattern into two and also dividing the energy distribution accompanying this division. It's okay.

Note that the prism used as the optical element for splitting light can be used by arranging it in any direction that can split the incident laser light into two.

(Effect of the invention) As is clear from the above, when the dye laser device according to this invention is used in a measurement device using the CARS method, the cross-sectional shapes of the pump light and Stokes light can be made into substantially equal half-moon-shaped patterns. As a result, spatial resolution is improved compared to conventional methods,
Furthermore, since the beam energy intensity outside the sample area can be made significantly lower than in the conventional case by pattern division, undesired CARS light that causes noise is not generated.

Therefore, by incorporating the dye laser device of this invention into a CARS measurement device, highly accurate measurement can be performed.

[Brief explanation of drawings]

FIG. 1 is a schematic diagram showing the structure of the dye laser of this invention, and FIGS. 2 and 3 are schematic diagrams showing the structure of a conventional dye laser device. 12...Dye cell, 14...Total reflection mirror, 1
6... Output mirror, 20... Optical element, 22...
Condensing lens, L ₁ ...excitation laser beam, L ₂ ...output light (dye laser or Stokes light), L ₃ ...one beam, ω ₁ ...pump light, P ₁ ...circular pattern, P ₃ ~ P ₇ ...Half-moon (semicircular) pattern, O...Optical axis.

Claims (1)

[Scope of utility model registration request] The input optical system is equipped with an optical element that splits the circular cross-sectional pattern of the excitation laser beam into two beams each having a cross-sectional pattern that can be regarded as a half-moon shape, and one of the divided beams can be regarded as a half-moon shape. A dye laser device characterized in that the dye laser is arranged so that the dye laser is oscillated with an output light that can be regarded as half-moon shaped by making the dye laser incident at an acute angle with respect to the optical axis of the dye laser and exciting the dye laser.