rus
Issue #3/2016
D.Oulianov, I.Kuratev, R.Biryukov, V.Konovalov, E.Fedyna
Son of Titan: Broadly Tunable High Energy Nanosecond Ti:Sapphire Laser TiSon GSB
Son of Titan: Broadly Tunable High Energy Nanosecond Ti:Sapphire Laser TiSon GSB
A novel broadly tunable gain-switched Ti:Sapphire laser has been developed specifically for photoacoustic imaging applications. Wavelength is electronically tuned in the range of 710–890 nm. Random wavelength access is possible with less than 50 ms switching time per any wavelength change.
Теги: optoacoustics ti:sapphire laser ti: sapphire лазер tunable laser перестраиваемый лазер фотоакустика
Photoacoustic (PA) or optoacoustic imaging becomes one of the fastest growing medical imaging techniques in the 21st century due to its ability to produce high spatial resolution images of tissues at deep depths unachievable by optical methods [1]. PA imaging utilizes a high energy laser illuminating the surface of the object under study followed by detection of acoustic waves generated by absorbed regions inside the object. Because of relatively deep light penetration of several cm into biological tissues and availability of high energy sources, the wavelength range of 700—900 nm is the most used region for PA imaging for biomedical applications. Many different techniques and variations of PA imaging has been introduced during the past two decades. Among them multi-wavelength (or multi-spectral) PA tomography and microscopy that have been gaining a lot of attention recently [2]. These techniques are based on PA signal detection generated by pulses of several different wavelengths simultaneously or sequentially exciting the object. Since absorption of different biological objects has strong wavelength selectivity, by choosing the right wavelength it is possible to significantly increase contrast of object of interest and by using several different wavelengths get an image of several objects in a single frame. In order to do such a measurement a high energy tunable laser is required. In case of live object study in order to prevent distortion due to breathing or blood pulsation this laser should also have fast wavelength switching available. The required energies are varying in the range of 0.1—100 mJ depending on the object studied and PA technique used. Another important laser requirement is short pulse duration which directly impacts the spatial resolution and usable acoustic wave bandwidth (e. g. less than 10 ns is usually needed for PA microscopy). In order to increase signal to noise ratio kHz pulse repetition rates are also desired.
In order to address the above requirements we have developed a tunable gain-switched Ti: Sapphire laser TiSon GSB (see Fig.1). The basic laser optical scheme is shown in Fig.2. We use a frequency doubled actively Q-switched diode-pumped Nd: YLF laser as a pump laser. It generates 1.0 mJ pulse energies at 527 nm. These pulses are focused into a Brewster cut Ti: Sapphire crystal placed into a resonator. A typical tuning curve of TiSon GSB is shown in Fig. 3. The pulse energy peaks at 800 nm and equals to 215 mj with 5 ns pulse duration at 1 kHz repetition rate. Even though the pulse duration somewhat increases at the ends of the tuning curve it still remains below 10 ns in the full tuning range (Fig.4). Laser line width equaled to about 0.5 nm for all wavelengths. The beam is a perfect TEM00 mode with M2<1,2 at all wavelengths. Fig.5 shows beam profile images measured by BeamStar beam profiler by Ophir-Spiricon at 720, 750, 800, 850 and 880 nm. Wavelength tuning is done by a proprietary wavelength selector placed into Ti: Sapphire resonator. The wavelength selector allows for a PC controlled wavelength switching with less than 50 ms time per any wavelength change. TiSon GSB is available with either air or 400 mm fiber output. Work on a higher energy model and even faster wavelength switching is in progress.
TiSon GSB have an ultra-compact footprint and contain both pump and Ti: Sapphire lasers in one housing. The laser head and the power supply dimensions are 237×56×165 and 230×80×193 mm3 respectively. Both the power supply and the laser head are air-cooled. The laser has rugged design, high stability and reliability. It may be employed for both industrial and scientific applications.
In order to address the above requirements we have developed a tunable gain-switched Ti: Sapphire laser TiSon GSB (see Fig.1). The basic laser optical scheme is shown in Fig.2. We use a frequency doubled actively Q-switched diode-pumped Nd: YLF laser as a pump laser. It generates 1.0 mJ pulse energies at 527 nm. These pulses are focused into a Brewster cut Ti: Sapphire crystal placed into a resonator. A typical tuning curve of TiSon GSB is shown in Fig. 3. The pulse energy peaks at 800 nm and equals to 215 mj with 5 ns pulse duration at 1 kHz repetition rate. Even though the pulse duration somewhat increases at the ends of the tuning curve it still remains below 10 ns in the full tuning range (Fig.4). Laser line width equaled to about 0.5 nm for all wavelengths. The beam is a perfect TEM00 mode with M2<1,2 at all wavelengths. Fig.5 shows beam profile images measured by BeamStar beam profiler by Ophir-Spiricon at 720, 750, 800, 850 and 880 nm. Wavelength tuning is done by a proprietary wavelength selector placed into Ti: Sapphire resonator. The wavelength selector allows for a PC controlled wavelength switching with less than 50 ms time per any wavelength change. TiSon GSB is available with either air or 400 mm fiber output. Work on a higher energy model and even faster wavelength switching is in progress.
TiSon GSB have an ultra-compact footprint and contain both pump and Ti: Sapphire lasers in one housing. The laser head and the power supply dimensions are 237×56×165 and 230×80×193 mm3 respectively. Both the power supply and the laser head are air-cooled. The laser has rugged design, high stability and reliability. It may be employed for both industrial and scientific applications.
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