An Analytical Expression Of The Photoacoustic Signal For A Pulsed Laser With A Sinusoidal Radial Profile

Öz

Photoacoustic signal depends on several laser factors, particularly the pulse duration, energy, wavelength, beam-width and repetition rate of the pulsed laser. Although these dependencies are well tested through experiments, they can also be investigated via theoretical approaches for the research into photoacoustic signal generation in parallel to advances in laser technologies. In this study, the photoacustic signal is presented analytically by solving the photoacoustic wave equation for an optical absorber heated up by a pulsed laser. The spatial and temporal parts of the pulsed laser are modeled by a sampling (sinc) function and a Gaussian function, respectively. The radial profile obtained experimentally by using a spatial light modulator can be modeled accurately with a sampling function. Pulsed lasers can lead to nonlinear effects. This nonlinear mechanism has various advantageous for the photoacoustic imaging. These short pulsed lasers have a close-to-sinusoidal variation in the central pulse region so that the spatial part of the laser is modeled by a sampling function in this work. For the photoacoustic wave, a detailed expression is obtained analytically in terms of the pulse duration and beam-width. The photoacoustic signal is observed in terms of time for various detector positions. Moreover, a detailed analysis is conducted to obtain a correlation between the photoacoustic signal and the laser factors. Therefore, the resulting quantification of the physical laser factors can offer a useful theoretical guide for the applications of photoacoustics. The sampling modeling presented by this study can also be helpful for the understanding of the nonlinear mechanism in photoacoustics.

Anahtar Kelimeler

• Photoacoustics
• Laser Parameters
• Spatiotemporal Profile

Sinüzoidal Uzaysal Kısma Sahip Kısa Atımlı Lazer Işığının Meydana Getirdiği Fotoakustik Sinyalin Analitik Olarak İfadesi

Öz

Fotoakustik sinyal lazer ışığının atım süresi, enerjisi, dalgaboyu ve atım sıklığı gibi parametrelere bağlıdır. Bu parametrelerin fotoakustik sinyal üzerindeki etkileri deneyler ile test edilebilmektedir. Bununla birlikte bu etkiler teorik yaklaşımlar aracılığıyla lazer teknolojilerine paralel olarak araştırılabilir. Bu çalışmada, Fourier dönüşümü yöntemi kullanılarak fotoakustik dalga denkleminin çözümleri oldukça kısa dalga boylu lazer ışığı tarafından uyarılmış küresel şekle sahip bir absorbe edici madde için elde edilmiştir. Darbeli lazerin uzaysal ve zamansal kısımları sırasıyla sinc ve Gaussian fonksiyonları ile modellenmiştir. Uzaysal ışık modülatörü kullanılarak deneysel olarak elde edilmiş olan darbeli lazerin radyal kısmı sinc fonkyonu ile gerçeğe yakın olarak modellenmektedir. Ayrıca, darbeli lazerler lineer olmayan etkiler meydana getirirler. Lineer olmayan bu mekanizma fotoakustik görüntüleme tekniğinde bir takım avantajlara sahiptir. Darbeli lazerler merkezi atım bölgesinde sinüzoidal bir değişime sahiptir. Bundan dolayı bu çalışmada lazerin uzaysal kısmı sinc fonksiyonu ile tasvir edilmiştir. Lazer parametrelerini (atım süresi ve dalga genişliği) içeren ayrıntılı bir fotoakustik dalga (sinyal) ifadesi analitik olarak elde edilmiştir. Fotoakustik sinyal zamana bağlı olarak çeşitli dedektör pozisyonlarında (absorbe edici madde dışında) zamana bağlı olarak ifade edilmiştir. Ayrıca, yapılan analiz sonucunda fotoakustik sinyal ile lazer parametreleri arasında bir korelasyon olduğu saptanmıştır. Sonuç olarak lazer parametrelerinin nicel olarak belirlenmesine imkan veren bu çalışma fotoakustik alanındaki uygulamalar için faydalı olabilir.

Anahtar Kelimeler

• Medikal Fizik
• Lazer
• Optik
• Fotoakustik
• Medikal Goruntuleme

Kaynakça

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