Femtosecond Cr:Forsterite Laser Mavericks - High Power System Jaws

		OUTPUT 65fs 250mW

  TECHNICAL DATA

* - depends on the pump power and operating temperature

Near Infrared Tunable Femtosecond Cr:Forsterite (Cr:F) Laser system at 1250 nm with Ytterbium Fiber Laser Pump: For Research and Industrial Applications

The femtosecond Cr:Forsterite (Cr:F) laser system from Del Mar Ventures is a mode-locked ultrashort laser producing pulses in near infrared ~1250 nm range. A laser is mode-locked when many longitudinal modes inside the laser cavity are held in phase by constructive interference producing the femtosecond (10 ^-15s) pulse.¹  Forsterite based on Cr⁴⁺ are the first tunable lasers operating in 1150 to 1300 nm range.^2,3,4,5  The extremely short time duration of a femtosecond pulse gives enormous peak powers and power densities. Femtosecond lasers are being used in a rapidly growing number of applications, including ultrafast photochemistry, photophysics, photoablation, micromachining, imaging condensed matter, semiconductor device physics, and other areas.

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The Cr:F gain medium is pumped by a 6 -10W Ytterbium Fiber Laser giving an all solid state laser system that is an affordable source of femtosecond pulses in 1230 - 1270nm region. The combination of Ytterbium Fiber Laser and Cr:F oscillator gives pulses in the sub-65 femtosecond range at a repetition rate of 120/76 MHz and delivers power between 180-250mW.

The femtosecond Cr:Forsterite laser is tunable over wavelengths from 1230 to 1270 nm, making it ideal for imaging condensed matter and biomedical applications.^6,7  Frequency doubling can produce wave lengths in the visible at ~630 nm and supercontinuum generation produce pulses in the infrared and visible range.

Multiphoton Confocal Microscopy Using a Femtosecond Cr:Forsterite Laser

New Photochemistry and Photobiology

With the high bandwidth and extremely short pulse duration of femtosecond lasers researchers are pushing the bounds of chemical and biological imaging. Laser spectroscopy involves the use of femtosecond laser pulses to study the properties of matter. The short pulse duration allows the detection and study of short-lived transient chemical reaction at very high resolutions.⁸

Optical coherence tomography (OCT) employs the coherent properties of the Cr:Forsterite light source to study the morphological structures and functions of biological samples on micron scale, such as cellular development with very high resolution.⁹ Because the axial resolution depends primarily on the bandwidth of the light source, high bandwidth femtosecond Cr:F lasers can give resolutions in the 5 - 10 um range with imaging depths of 2 - 3 mm. Cells as small as 15um have been successfully imaged using Cr:F lasers and OCT. ⁷ 

The Cr:Forsterite generates femtosecond pulses at wavelengths from 1230 to 1270 nm. These wavelengths are less damaging to biological samples than the shorter wavelengths produced by other femtosecond lasers. This allows in vivo imaging of cells and other biological samples.  With wavelength above 1200nm it is possible to image tissue samples that are non transparent at shorter wavelengths. This wavelength is ideal to heat water in tissues for welding, stress release, cornea shaping and other applications.

Material processing

The femtosecond pulse duration is very short making even low energy pulses produce extremely high peak power. This limits low energy threshold thermal and mechanical side effects.  The high peak power of the femtosecond pulse allows multiple photons to be absorbed, creating an electron plasma in the material.   As the plasma expands material is ejected from the target area. ¹⁰  Because this material ablation is not a thermal effect, cavitations and laser induced pressure transients are reduced.

Femtosecond lasers are used to produce micro-gratings and multi-dimension periodic nano structures in a variety of materials including dielectrics, semiconductors, metals, plastics and resins. ¹¹ Multiphoton absorption allows for processing of materials that are not very photosensitive. 

Below the ablation threshold the high pulse energies can introduce structural changes resulting in a change in the index of refraction of the material. All optical wave guides and photonic devices are manufactured using these techniques. ¹²

Medical Applications

Femtosecond lasers are finding many uses in the medical field where they are finding use in applications ranging from biopsy imaging to eye surgery.

The same properties that make femtosecond lasers useful for material processing can also be used for a variety of surgical applications.   One of the first commercially successful applications of femtosecond lasers is their use in the LASIK (Laser in situ keratomileusis) eye surgery procedure. Cr⁴⁺ lasers in 1110-1500 nm range offer safer wavelengths than Ti:sapphire femtosecond lasers at 800 nm to reduce potential retinal damage. The Ultrafast laser replaces the microkeratome mechanical knife that makes the initial cut in the cornea.  This offers a highly controlled cut of uniform thickness that is not possible with a mechanical knife.¹³  Dental applications and surgery on the inner ear are areas where the extremely clean material processing abilities of femtosecond lasers offer an alternative to mechanical drills or CW lasers that leave micro cracks and cause thermal stress in tooth enamel and tissue damage in the inner ear.^13,14

Work has also been done using femtosecond lasers to treat atherosclerosis. The build up of plaque causes arteries to harden, restricting blood flow.  By ablating tissue from the artery wall the elasticity of the artery can be restored.  Blood pressure forces the artery to expand once wall material has been removed.  This procedure would be used in place of balloon angioplasty or Stenting procedures. The use of laser ablation offers the advantage of being less damaging to the structural integrity of the artery than other procedures.¹³

Femtosecond Cr:Forsterite laser presentation (Power Point)

References

1.                  L.  Qian, X. Liu, F. Wise,” Femtosecond Kerr-lens mode locking with negative nonlinear phase shifts,” Opt. Lett. Vol. 24, No. 3, (1999).

2.                  V. Petricevic, S. K. Gayen, and R. R. Alfano, "Laser Action in Chromium-Activated Forsterite for Near-Infrared Excitation: Is Cr⁴⁺ the Lasing Ion?" Appl. Phys. Lett. 53, 2590 (1988).

3.                  V. Petricevic, A. Seas, and R. R. Alfano, "Slope Efficiency Measurements of Chromium-Doped Forsterite Laser", Opt. Lett. 16, 811 (1991).

4.                  A. Seas, V. Petricevic, and R. R. Alfano, "Generation of Sub-100-fs Pulses From a Continuous-Wave Mode-Locked Chromium-Doped Forsterite Laser", Opt. Lett. 17, 937 (1992).

5.                  J. M. Evans, V. Petricevic, A. B. Bykov, A. Delgado, and R. R. Alfano, “Direct Diode-Pumped Continuous-Wave Near-Infrared Tunable Laser Operation of Cr⁴⁺:forsterite and Cr⁴⁺:Ca₂GeO₄”, Opt. Lett. 22, 1171 (1997).

6.                  S. Boppart, W. Drexler, U. Morgner, F. Kartner, J. Fujimoto, “Ultrahigh Resolution and Spectroscopic OCT Imaging of Cellular Morphology and Function,” Proc. Inter-Institute Workshop on In Vivo Optical Imaging at the National Institutes of Health. Ed. A. H. Gandjbakhche. September 16-17, pp. 56-61, 1999.

7.                  W. Drexler, U. Morgner, F. Kartner, C. Pitris, S. Boppart, X. Li, J. Fujimoto, “In vivo  ultrahigh-resolution optical coherence tomography,”  Opt. Lett. Vol. 24, No. 17, (1999). 

8.                  W. Sibbett, D. Reid, M. Ebrahimzadeh, “Versatile femtosecond laser sources for time-resolved studies: configurations and characterizations,” Phil. Trans. R. Soc. Lond. A 356, 283-296, (1998)

9.                  A. Nejadmalayeri, “Optical Coherence Tomography,” (2001)

10.              V. Mizeikis et al., J. Nishii, S. Matsuo et al.,” Femtosecond laser micro-fabrication for tailoring photonic crystals in resins and silica,” Journal Photochemistry and Photobiology A: Chem. 145, (2001)

11.              M. Hirano, K. Kawamura, H. Hosona, “ Encoding of holographic grating and periodic nano-structure by femtosecond laser pulse,” Applied Surface Science 197-198, 688-698 (2002).

12.              K. Minoshima, A. Kowaleviez, E. Ippen, J. Fujimoto, “Fabrication of coupled mode photonic devices in glass by nonlinear femtosecond laser materials processing,” Optics Express 645, Vol.10, No.15, (2002).

13.              H. Lubatschowski,  A. Heisterkamp,  F. Will,  A. Singh,  J. Serbin,  A. Ostendorf,  O. Kermani,  R. Heermann, H. Welling, W. Ertmer, “Medical applications for ultrashort laser pulses,” RIKEN Rev., No. 50 (2003).

14.             A. Rode, E. Gamaly, B. Luther-Davis, A. Chan, R. Lowe, P. Hannaford, “Subpicosecond laser ablation of dental enamel,” J. Applied Physics Vol. 92, No. 4, (2002).

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