Method and apparatus for improving the dynamic range of laser detected ultrasound in attenuative materials

A system for detecting ultrasonic displacements in a material under test comprising:

• a seed laser light source that provides a first laser beam having a path of propagation;
• a modulator assembly placed in said path of propagation operable to provide for time-varying of output pulse having a time-dependent pulse profile;
• a controller operable to direct said modulator assembly;
• at least one optical isolation assembly placed in said path of propagation that prevents reflected laser light feedback into said seed laser light source;
• at least one optical beam dump positioned with respect to said at least one optical isolation assembly in order absorb reflected laser light feedback isolated by said optical isolation assembly;
• at least one laser light amplification assembly placed in said path of propagation in order to amplify said first laser beam;
• an ultrasonic induction system which induces ultrasonic displacements into the material under test;
• a detection system which applies said output pulse to the material under test, detects ultrasonic displacements in the material under test, and generates at least one output signal;
• and
• a data processor to process said at least one output signal in order to obtain data representative of said ultrasonic displacements in the material under test.

A method for detecting ultrasonic displacements in a material under test, comprising the steps of:

• generating the ultrasonic displacements in the material under test;
• generating a first laser pulse having a time-dependent pulse profile;
• applying said first laser pulse to the material under test;
• detecting the laser light of said first laser pulse modulated by the ultrasonic displacements at the material under test;
• and
• converting said modulated laser light into at least one output signal containing data representative of the ultrasonic displacements in the material under test.