Laser device and photoacoustic measurement device

1. A laser device comprising: a laser rod which includes alexandrite crystal;

an excitation light source which irradiates the laser rod with excitation light; a resonator which includes a pair of mirrors with the laser rod sandwiched therebetween; a Q switch which is inserted into the optical path of the resonator and controls the Q value of the resonator; and

a non-coated Brewster polarizer which is inserted at least between the laser rod and the Q switch or between the laser rod and one of the pair of mirrors and selectively transmits light in a predetermined polarization direction among light emitted from the laser rod,

wherein the Q switch includes a Pockels cell, in a case in which an applied voltage to the Pockels cell is a first voltage, the Q value of the resonator is higher than a laser oscillation threshold, and in a case in which the applied voltage is a second voltage higher than the first voltage, the Q value of the resonator is equal to or less than the laser oscillation threshold, and

wherein, in a case in which an input energy to the excitation light source is 20 J, the range of an applied voltage to the Q switch for making the Q value of the resonator equal to or less than the laser oscillation threshold is equal to or greater than 0.5 kV.

2. The laser device according to claim 1 ,

wherein the optical path of the resonator is sealed within the range of the resonator.

3. The laser device according to claim 1 ,

wherein at least one of the laser rod or the Q switch has an anti-reflection film at a light incidence end thereof.

4. The laser device according to claim 2 ,

wherein at least one of the laser rod or the Q switch has an anti-reflection film at a light incidence end thereof.

5. The laser device according to claim 1 ,

wherein the first voltage is 0 V, and the second voltage is a voltage which makes the Pockets cell function as a quarter-wave plate.

6. The laser device according to claim 1 ,

wherein the polarizer is constituted of a glass plate disposed at a Brewster angle with respect to the optical axis of light emitted from the laser rod.

7. The laser device according to claim 2 ,

wherein the polarizer is constituted of a glass plate disposed at a Brewster angle with respect to the optical axis of light emitted from the laser rod.

8. The laser device according to claim 1 ,

wherein, in a case in which input energy is 20 J, the output energy of laser is equal to or greater than 140 mJ.

9. The laser device according to claim 1 ,

wherein the polarizer is inserted between the laser rod and the output-side mirror of the pair of mirrors.

10. The laser device according to claim 1 ,

wherein the polarizers are inserted both between the laser rod and the Q switch and between the laser rod and one of the pair of mirrors.

11. A laser device comprising: a laser rod which includes alexandrite crystal;

an excitation light source which irradiates the laser rod with excitation light; a resonator which includes a pair of mirrors with the laser rod sandwiched therebetween; a Q switch which is inserted into the optical path of the resonator and controls the Q value of the resonator; and

a Brewster polarizer which is inserted at least between the laser rod and the Q switch or between the laser rod and one of the pair of mirrors, selectively transmits light in a predetermined polarization direction among light emitted from the laser rod, and has a film for separating light in the predetermined polarization direction from light in a polarization direction orthogonal to the predetermined polarization direction,

wherein the Q switch includes a Pockets cell, in a case in which an applied voltage to the Pockels cell is a first voltage, the Q value of the resonator is higher than a laser oscillation threshold, and in a case in which the applied voltage is a second voltage higher than the first voltage, the Q value of the resonator is equal to or less than the laser oscillation threshold, and

wherein, in a case in which an input energy to the excitation light source is 20 J, the range of an applied voltage to the Q switch for making the Q value of the resonator equal to or less than the laser oscillation threshold is equal to or greater than 2.5 kV.

12. The laser device according to claim 11 ,

wherein, in a case in which input energy is 20 J, the output energy of laser is equal to or greater than 140 mJ.

13. A photoacoustic measurement device comprising:

the laser device according to claim 1 ;

photoacoustic detection unit which detects a photoacoustic wave generated in a subject after the subject is irradiated with a laser beam emitted from the laser device; and

signal processing unit which performs signal processing based on the detected photoacoustic wave.

14. The laser device according to claim 1 ,

wherein the non-coated Brewster polarizer is a non-coated glass plate of quartz glass or borosilicate glass, disposed at a Brewster angle.

15. The laser device according to claim 1 ,

wherein the laser rod has a diameter equal to or less than 4 mm, and a rod length of laser rod is equal to or less than 70 mm.

16. The laser device according to claim 11 ,

wherein the non-coated Brewster polarizer is a non-coated glass plate of quartz glass or borosilicate glass, disposed at a Brewster angle.

17. The laser device according to claim 11 ,

wherein the laser rod has a diameter equal to or less than 4 mm, and a rod length of laser rod is equal to or less than 70 mm.