Rainer J. Beck

Application of cooled spatial light modulator for high power nanosecond laser micromachining

The application of a commercially available spatial light modulator (SLM) to control the spatial intensity distribution of a nanosecond pulsed laser for micromachining is described for the first time. Heat sinking is introduced to increase the average power handling capabilities of the SLM beyond recommended limits by the manufacturer. Complex intensity patterns are generated, using the Inverse Fourier Transform Algorithm, and example laser machining is demonstrated. The SLM enables both complex beam shaping and also beam steering.

Application of a liquid crystal spatial light modulator to laser marking

Laser marking is demonstrated using a nanosecond (ns) pulse duration laser in combination with a liquid crystal spatial light modulator to generate two-dimensional patterns directly onto thin films and bulk metal surfaces. Previous demonstrations of laser marking with such devices have been limited to low average power lasers. Application in the ns regime enables more complex, larger scale marks to be generated with more widely available and industrially proven laser systems. The dynamic nature of the device is utilized to improve mark quality by reducing the impact of the inherently speckled intensity distribution across the generated image and reduce thermal effects in the marked surface.

Adaptive extracavity beam shaping for application in nanosecond laser micromachining

The typical Gaussian intensity distribution generated at focus of a laser machining workstation is not always ideal for the application; instead other shapes such as ellipses, flat-tops (circular or square), or doughnuts can in some cases give better results. Also, other more complex beam profiles might be beneficial for surface micro structuring. In order to realise, and rapidly change between such beam shapes, we are investigating an adaptive optics approach based on using an iterative simulated annealing algorithm to control the actuators of a deformable mirror. A 37-element piezoelectric deformable mirror and a 37-element bimorph mirror were applied in an extracavity arrangement. Beam shaping results with these systems are presented and example laser machining is demonstrated in this paper. The results enabled by the deformable mirrors are compared to previous results using a spatial light modulator (SLM) based on a liquid crystal microdisplay. The SLM has a much higher resolution and enables complex beam shapes to be generated, however is much slower in response. Having an active beam shaping element incorporated in a laser machining workstation adds increased flexibility and improves process control.

Compensation for time fluctuations of phase modulation in a liquid-crystal-on-silicon display by process synchronization in laser materials processing.

We demonstrate the adverse influence of temporal fluctuations of the phase modulation of a spatial light modulator (SLM) display device on nanosecond laser micromachining. We show that active cooling of the display reduces the amplitude of these fluctuations, and we demonstrate a process synchronization technique developed to compensate for these fluctuations when applying the SLM to laser materials processing. For alternative SLM devices developed specifically for laser wavefront control (which do not exhibit such flickering problems), we show that our process synchronization approach is also beneficial to avoid machining glitches when switching quickly between different phase profiles (and hence beam patterns).

Application of adaptive optics to laser micromachining

For many laser machining applications it is common to use some form of beam shaping to modify the typically Gaussian intensity distribution of the laser to generate an intensity profile that is more appropriate for the task. For example refractive elements may be used to generate top hat intensity distributions which are better suited to drilling applications or more complex profiles may be generated to mark patterns on a surface either with diffractive elements or masks. Dynamic beam shaping elements offer an advantage in terms of changing between shapes rapidly to quickly mark a series of shapes across a surface or even to modify the beam shape during a machining operation.Machining demonstrations are presented with two types of adaptive optics (AO’s) using millisecond and nanosecond pulsed lasers. The first AO is a piezoelectric deformable mirror capable of supporting high average powers and enabling rapid (∼1 kHz) modification of the mode shape of a beam. The second is a liquid crystal spatial light modulator which, although slower in response (75 Hz), can generate complex arbitrary shapes. The dynamic nature of these elements is used to improve the quality of laser machining results.For many laser machining applications it is common to use some form of beam shaping to modify the typically Gaussian intensity distribution of the laser to generate an intensity profile that is more appropriate for the task. For example refractive elements may be used to generate top hat intensity distributions which are better suited to drilling applications or more complex profiles may be generated to mark patterns on a surface either with diffractive elements or masks. Dynamic beam shaping elements offer an advantage in terms of changing between shapes rapidly to quickly mark a series of shapes across a surface or even to modify the beam shape during a machining operation.Machining demonstrations are presented with two types of adaptive optics (AO’s) using millisecond and nanosecond pulsed lasers. The first AO is a piezoelectric deformable mirror capable of supporting high average powers and enabling rapid (∼1 kHz) modification of the mode shape of a beam. The second is a liquid crystal spatial light m...

Precision resection of lung cancer in a sheep model using ultrashort laser pulses

Recent developments and progress in the delivery of high average power ultrafast laser pulses enable a range of novel minimally invasive surgical procedures. Lung cancer is the leading cause of cancer deaths worldwide and here the resection of lung tumours by means of picosecond laser pulses is presented. This represents a potential alternative to mitigate limitations of existing surgical treatments in terms of precision and collateral thermal damage to the healthy tissue. Robust process parameters for the laser resection are demonstrated using ovine pulmonary adenocarcinoma (OPA). OPA is a naturally occurring lung cancer of sheep caused by retrovirus infection that has several features in common with some forms of human pulmonary adenocarcinoma, including a similar histological appearance, which makes it ideally suited for this study. The picosecond laser was operated at a wavelength of 515 nm to resect square cavities from fresh ex-vivo OPA samples using a range of scanning strategies. Process parameters are presented for efficient ablation of the tumour with clear margins and only minimal collateral damage to the surrounding tissue. The resection depth can be controlled precisely by means of the pulse energy. By adjusting the overlap between successive laser pulses, deliberate heat transfer to the tissue and thermal damage can be achieved. This can be beneficial for on demand haemostasis and laser coagulation. Overall, the application of ultrafast lasers for the resection of lung tumours has potential to enable significantly improved precision and reduced thermal damage to the surrounding tissue compared to conventional techniques.

Investigation of the efficacy of ultrafast laser in large bowel excision

Local resection of early stage tumors in the large bowel via colonoscopy has been a widely accepted surgical modality for colon neoplasm treatment. The conventional electrocautery techniques used for the resection of neoplasia in the mucosal or submucosal layer of colon tissue has been shown to create obvious thermal necrosis to adjacent healthy tissues and lacks accuracy in resection. Ultrafast picosecond (ps) laser ablation using a wavelength of 1030 or 515 nm is a promising surgical tool to overcome the limitations seen with conventional surgical techniques. The purpose of this initial study is to analyze the depth of ablation or the extent of coagulation deployed by the laser as a function of pulse energy and fluence in an ex-vivo porcine model. Precise control of the depth of tissue removal is of paramount importance for bowel surgery where bowel perforation can lead to morbidity or mortality. Thus we investigate the regimes that are optimal for tissue resection and coagulation through plasma mediated ablation of healthy colon tissue. The ablated tissue samples were analyzed by standard histologic methods and a three dimensional optical profilometer technique. We demonstrate that ultrafast laser resection of colonic tissue can minimize the region of collateral thermal damage (<50 μm) with a controlled ablation depth. This surgical modality allows potentially easier removal of early stage lesions and has the capability to provide more control to the surgeon in comparison with a mechanical or electrocautery device.

Precision resection of intestine using ultrashort laser pulses

Endoscopic resection of early colorectal neoplasms typically employs electrocautery tools, which lack precision and run the risk of full thickness thermal injury to the bowel wall with subsequent perforation. We present a means of endoluminal colonic ablation using picosecond laser pulses as a potential alternative to mitigate these limitations. High intensity ultrashort laser pulses enable nonlinear absorption processes, plasma generation, and as a consequence a predominantly non-thermal ablation regimen. Robust process parameters for the laser resection are demonstrated using fresh ex vivo pig intestine samples. Square cavities with comparable thickness to early colorectal neoplasms are removed for a wavelength of 1030 nm and 515 nm using a picosecond laser system. The corresponding histology sections exhibit in both cases only minimal collateral damage to the surrounding tissue. The ablation depth can be controlled precisely by means of the pulse energy. Overall, the application of ultrafast lasers for the resection of intestine enables significantly improved precision and reduced thermal damage to the surrounding tissue compared to conventional electrocautery.

Precision machining of pig intestine using ultrafast laser pulses

Endoluminal surgery for the treatment of early stage colorectal cancer is typically based on electrocautery tools which imply restrictions on precision and the risk of harm through collateral thermal damage to the healthy tissue. As a potential alternative to mitigate these drawbacks we present laser machining of pig intestine by means of picosecond laser pulses. The high intensities of an ultrafast laser enable nonlinear absorption processes and a predominantly nonthermal ablation regime. Laser ablation results of square cavities with comparable thickness to early stage colorectal cancers are presented for a wavelength of 1030 nm using an industrial picosecond laser. The corresponding histology sections exhibit only minimal collateral damage to the surrounding tissue. The depth of the ablation can be controlled precisely by means of the pulse energy. Overall, the application of ultrafast lasers to ablate pig intestine enables significantly improved precision and reduced thermal damage to the surrounding tissue compared to conventional techniques.

Freeform laser manufacturing based on a parallel robot platform

We present the concept for a novel 3D laser-based freeform fabrication platform that combines the ability to construct and add material to freeform shapes with the metrology of the created part and the ability to remove material. The synergy of these processes offers the potential to enable a high level of form fit and low tolerances in excess of that achievable in freeform manufacture alone. Our approach is based on a parallel kinematic robot platform with advantages in terms of accuracy, speed and costs compared to serial robot arms.We present the concept for a novel 3D laser-based freeform fabrication platform that combines the ability to construct and add material to freeform shapes with the metrology of the created part and the ability to remove material. The synergy of these processes offers the potential to enable a high level of form fit and low tolerances in excess of that achievable in freeform manufacture alone. Our approach is based on a parallel kinematic robot platform with advantages in terms of accuracy, speed and costs compared to serial robot arms.