Birefringent Filter Rotation for Fast Laser Wavelength Switching
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Solution Overview
Problem
Existing photoacoustic imaging systems face challenges in switching between different laser wavelengths quickly and accurately, leading to mismatching of photoacoustic signals when imaging moving objects, as they require adjusting wavelength selection elements for each wavelength emission, limiting the ability to emit a desired wavelength sequence.
Innovation Solution
A laser light source unit with a birefringent filter and Q switch, controlled by a rotation unit, allows for sequential emission of pulse laser beams in a predetermined wavelength sequence by rotating the birefringent filter at a predetermined speed, enabling precise timing of Q switch activation to produce pulse laser beams of specific wavelengths.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If a wavelength selection element (etalon or birefringent filter) is adjusted to switch between different laser wavelengths, then the desired wavelength can be emitted, but the switching time increases and signal mismatching occurs when imaging moving objects
Solution Approach 1:
The birefringent filter is rotated in advance at a predetermined speed before laser emission to position the desired wavelength in the optical path. This preliminary positioning allows the Q-switch to immediately generate the desired wavelength without delay during actual emission, resolving the contradiction between wavelength adaptability and switching time
Solution Approach 2:
The system dynamically controls the rotation speed of the birefringent filter based on the required wavelength sequence. By making the rotation speed adjustable and synchronized with the laser emission timing, the system achieves both wavelength versatility and minimal switching time
2Measurement precision
If the wavelength selection element is adjusted for each laser emission, then precise wavelength control is achieved, but the system complexity and operational difficulty increase
Solution Approach 1:
The birefringent filter automatically rotates through the complete wavelength range at a predetermined speed, and the Q-switch automatically triggers emission at the appropriate timing. This self-synchronized operation eliminates the need for manual adjustment and complex control mechanisms, reducing device complexity while maintaining precise wavelength control
Solution Approach 2:
The birefringent filter rotates periodically at a predetermined speed, creating a repeating sequence of wavelengths. This periodic rotation simplifies the control system by eliminating the need for complex positioning mechanisms, as the desired wavelength will naturally appear at regular intervals during rotation
3Productivity
If the birefringent filter rotates at high speed to reduce switching time, then the number of selectable wavelengths increases, but the precision of wavelength selection decreases
Solution Approach 1:
The system incorporates a rotational position detection mechanism that provides feedback on the birefringent filter's angular position. This feedback allows the control system to precisely determine when the desired wavelength is in position and trigger the Q-switch at the optimal moment, maintaining wavelength selection accuracy even at high rotation speeds
Solution Approach 2:
The system replaces manual mechanical adjustment of the birefringent filter with an automated rotation mechanism driven by a motor. This substitution allows for precise control of rotation speed and position through electrical signals rather than mechanical manipulation, maintaining accuracy while enabling faster switching
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This configuration enables efficient and accurate switching between multiple wavelengths, reducing signal mismatch and allowing for the generation of photoacoustic images with improved resolution and accuracy, particularly in imaging moving subjects.
Implementation Method 1
a birefringent filter which is inserted into the optical resonator and changes an oscillation wavelength of the optical resonator in association with rotational displacement of the birefringent filter
Implementation Method 2
a Q switch which is inserted into the optical resonator... an emission control unit that... turns on the Q switch... to cause the pulse laser beam to be emitted
Implementation Method 3
an excitation light source that irradiates the laser rod with excitation light
Implementation Method 4
a laser rod... an excitation light source that irradiates the laser rod with excitation light
Implementation Method 5
an optical resonator including a pair of mirrors facing each other with the laser rod interposed therebetween
Implementation Method 6
a photoacoustic image forming apparatus that forms an image of the inside of a living body using a photoacoustic effect... Body tissues absorbing energy of the pulsed light expand in volume inside the living body irradiated with the pulsed light, and thus acoustic waves are generated
Data Source
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AI summary
A pulse laser beam is emitted in a desired wavelength sequence using a laser light source unit. A Q switch and a birefringent filter are inserted into an optical resonator including a pair of mirrors and facing each other with a laser rod interposed therebetween. The birefringent filter changes an oscillation wavelength of the optical resonator in association with rotational displacement. The rotation control unit rotates the birefringent filter at a predetermined rotation speed depending on the number of wavelengths included in the wavelength sequence of the pulse laser beam to be emitted. An emission control unit irradiates the laser rod with excitation light, and then turns on the Q switch at a timing when a rotational-displacement-position of the birefringent filter is set to a position corresponding to the wavelength of the pulse laser beam to be emitted, to cause the pulse laser beam to be emitted.